Get only number of working days between two days in javascript

Get only number of working days between two days in javascript - javascript

I have to calculate variables in javascript after x days from current day.I have to add some number of days based on some input parameter.
var currentDate = new Date();
var dd = currentDate.getDate();
var mm = currentDate.getMonth()+1;
var yyyy = currentDate.getFullYear();
if(dd<10) {
dd='0'+dd
}
if(mm<10) {
mm='0'+mm
}
currentDate= mm+'/'+dd+'/'+yyyy;
Now I want to get some date after 28 days from currentDate variable but it should not include Saturday and Sunday.
So my question is how to exclude the weekends (2 days) from the 28 (for example).
Any help will be appreciated.

Here's a generic function to add n business days to a date
function addDays(dt, n) {
var rem = n % 5;
var add = 7 * (n - rem) / 5 + rem;
var ret = new Date(dt);
ret.setDate(ret.getDate() + add);
if (ret.getDay() == 6) ret.setDate(ret.getDate() + 2);
else if (ret.getDay() == 0) ret.setDate(ret.getDate() + 1);
return ret;
}

This is really simple. Script below goes through all days between start and end date and checks if it isn't Saturday (tmpDate.getDay() != 6) or Sunday (tmpDate.getDay() != 0)
var start = new Date();
var end = new Date(2016, 6, 1);
var allDays = Math.floor((end.getTime() - start.getTime())/ 86400000);
var workingDays = 0;
for(var i = 0; i < allDays; i++){
var tmpDate = new Date();
tmpDate.setTime(today.getTime() + i * 24*60*60*1000);
if(tmpDate.getDay() != 0 && tmpDate.getDay() != 6)
wokringDays++;
}
alert(workingDays);

This will give you the number of working days:
function getWorkingDays(currentDateObj, numberOfDays)
{
if(numberOfDays < 0) return false;
var futureDateObj = new Date();
futureDateObj.setDate(currentDateObj.getDate() + numberOfDays);
var daysCnt = 1 + Math.round((futureDateObj.getTime()-currentDateObj.getTime())/(24*3600*1000));
var weekCnt = Math.floor( (currentDateObj.getDay() + daysCnt) / 7 );
var weekends = 2 * weekCnt + (currentDateObj.getDay()==0) - (futureDateObj.getDay()==6);
return numberOfDays - weekends;
}
console.log(getWorkingDays(new Date(), 28));

Related

Not able to get the result date/hours [duplicate]

How can I calculate an age in years, given a birth date of format YYYYMMDD? Is it possible using the Date() function?
I am looking for a better solution than the one I am using now:
var dob = '19800810';
var year = Number(dob.substr(0, 4));
var month = Number(dob.substr(4, 2)) - 1;
var day = Number(dob.substr(6, 2));
var today = new Date();
var age = today.getFullYear() - year;
if (today.getMonth() < month || (today.getMonth() == month && today.getDate() < day)) {
age--;
}
alert(age);

Try this.
function getAge(dateString) {
var today = new Date();
var birthDate = new Date(dateString);
var age = today.getFullYear() - birthDate.getFullYear();
var m = today.getMonth() - birthDate.getMonth();
if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
age--;
}
return age;
}
I believe the only thing that looked crude on your code was the substr part.
Fiddle: http://jsfiddle.net/codeandcloud/n33RJ/

I would go for readability:
function _calculateAge(birthday) { // birthday is a date
var ageDifMs = Date.now() - birthday.getTime();
var ageDate = new Date(ageDifMs); // miliseconds from epoch
return Math.abs(ageDate.getUTCFullYear() - 1970);
}
Disclaimer: This also has precision issues, so this cannot be completely trusted either. It can be off by a few hours, on some years, or during daylight saving (depending on timezone).
Instead I would recommend using a library for this, if precision is very important. Also #Naveens post, is probably the most accurate, as it doesn't rely on the time of day.

Important: This answer doesn't provide an 100% accurate answer, it is off by around 10-20 hours depending on the date.
There are no better solutions ( not in these answers anyway ). - naveen
I of course couldn't resist the urge to take up the challenge and make a faster and shorter birthday calculator than the current accepted solution.
The main point for my solution, is that math is fast, so instead of using branching, and the date model javascript provides to calculate a solution we use the wonderful math
The answer looks like this, and runs ~65% faster than naveen's plus it's much shorter:
function calcAge(dateString) {
var birthday = +new Date(dateString);
return ~~((Date.now() - birthday) / (31557600000));
}
The magic number: 31557600000 is 24 * 3600 * 365.25 * 1000
Which is the length of a year, the length of a year is 365 days and 6 hours which is 0.25 day. In the end i floor the result which gives us the final age.
Here is the benchmarks: http://jsperf.com/birthday-calculation
To support OP's data format you can replace +new Date(dateString);
with +new Date(d.substr(0, 4), d.substr(4, 2)-1, d.substr(6, 2));
If you can come up with a better solution please share! :-)

Clean one-liner solution using ES6:
const getAge = birthDate => Math.floor((new Date() - new Date(birthDate).getTime()) / 3.15576e+10)
// today is 2018-06-13
getAge('1994-06-14') // 23
getAge('1994-06-13') // 24
I am using a year of 365.25 days (0.25 because of leap years) which are 3.15576e+10 milliseconds (365.25 * 24 * 60 * 60 * 1000) respectively.
It has a few hours margin so depending on the use case it may not be the best option.

With momentjs:
/* The difference, in years, between NOW and 2012-05-07 */
moment().diff(moment('20120507', 'YYYYMMDD'), 'years')

Some time ago I made a function with that purpose:
function getAge(birthDate) {
var now = new Date();
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
// days since the birthdate
var days = Math.floor((now.getTime() - birthDate.getTime())/1000/60/60/24);
var age = 0;
// iterate the years
for (var y = birthDate.getFullYear(); y <= now.getFullYear(); y++){
var daysInYear = isLeap(y) ? 366 : 365;
if (days >= daysInYear){
days -= daysInYear;
age++;
// increment the age only if there are available enough days for the year.
}
}
return age;
}
It takes a Date object as input, so you need to parse the 'YYYYMMDD' formatted date string:
var birthDateStr = '19840831',
parts = birthDateStr.match(/(\d{4})(\d{2})(\d{2})/),
dateObj = new Date(parts[1], parts[2]-1, parts[3]); // months 0-based!
getAge(dateObj); // 26

Here's my solution, just pass in a parseable date:
function getAge(birth) {
ageMS = Date.parse(Date()) - Date.parse(birth);
age = new Date();
age.setTime(ageMS);
ageYear = age.getFullYear() - 1970;
return ageYear;
// ageMonth = age.getMonth(); // Accurate calculation of the month part of the age
// ageDay = age.getDate(); // Approximate calculation of the day part of the age
}

Alternate solution, because why not:
function calculateAgeInYears (date) {
var now = new Date();
var current_year = now.getFullYear();
var year_diff = current_year - date.getFullYear();
var birthday_this_year = new Date(current_year, date.getMonth(), date.getDate());
var has_had_birthday_this_year = (now >= birthday_this_year);
return has_had_birthday_this_year
? year_diff
: year_diff - 1;
}

function age()
{
var birthdate = $j('#birthDate').val(); // in "mm/dd/yyyy" format
var senddate = $j('#expireDate').val(); // in "mm/dd/yyyy" format
var x = birthdate.split("/");
var y = senddate.split("/");
var bdays = x[1];
var bmonths = x[0];
var byear = x[2];
//alert(bdays);
var sdays = y[1];
var smonths = y[0];
var syear = y[2];
//alert(sdays);
if(sdays < bdays)
{
sdays = parseInt(sdays) + 30;
smonths = parseInt(smonths) - 1;
//alert(sdays);
var fdays = sdays - bdays;
//alert(fdays);
}
else{
var fdays = sdays - bdays;
}
if(smonths < bmonths)
{
smonths = parseInt(smonths) + 12;
syear = syear - 1;
var fmonths = smonths - bmonths;
}
else
{
var fmonths = smonths - bmonths;
}
var fyear = syear - byear;
document.getElementById('patientAge').value = fyear+' years '+fmonths+' months '+fdays+' days';
}

I think that could be simply like that:
function age(dateString){
let birth = new Date(dateString);
let now = new Date();
let beforeBirth = ((() => {birth.setDate(now.getDate());birth.setMonth(now.getMonth()); return birth.getTime()})() < birth.getTime()) ? 0 : 1;
return now.getFullYear() - birth.getFullYear() - beforeBirth;
}
age('09/20/1981');
//35
Works also with a timestamp
age(403501000000)
//34

That's the most elegant way for me:
const getAge = (birthDateString) => {
const today = new Date();
const birthDate = new Date(birthDateString);
const yearsDifference = today.getFullYear() - birthDate.getFullYear();
if (
today.getMonth() < birthDate.getMonth() ||
(today.getMonth() === birthDate.getMonth() && today.getDate() < birthDate.getDate())
) {
return yearsDifference - 1;
}
return yearsDifference;
};
console.log(getAge('2018-03-12'));

This question is over 10 years old an nobody has addressed the prompt that they already have the birth date in YYYYMMDD format?
If you have a past date and the current date both in YYYYMMDD format, you can very quickly calculate the number of years between them like this:
var pastDate = '20101030';
var currentDate = '20210622';
var years = Math.floor( ( currentDate - pastDate ) * 0.0001 );
// 10 (10.9592)
You can get the current date formatted as YYYYMMDD like this:
var now = new Date();
var currentDate = [
now.getFullYear(),
('0' + (now.getMonth() + 1) ).slice(-2),
('0' + now.getDate() ).slice(-2),
].join('');

To test whether the birthday already passed or not, I define a helper function Date.prototype.getDoY, which effectively returns the day number of the year. The rest is pretty self-explanatory.
Date.prototype.getDoY = function() {
var onejan = new Date(this.getFullYear(), 0, 1);
return Math.floor(((this - onejan) / 86400000) + 1);
};
function getAge(birthDate) {
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
var now = new Date(),
age = now.getFullYear() - birthDate.getFullYear(),
doyNow = now.getDoY(),
doyBirth = birthDate.getDoY();
// normalize day-of-year in leap years
if (isLeap(now.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyNow--;
if (isLeap(birthDate.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyBirth--;
if (doyNow <= doyBirth)
age--; // birthday not yet passed this year, so -1
return age;
};
var myBirth = new Date(2001, 6, 4);
console.log(getAge(myBirth));

I just had to write this function for myself - the accepted answer is fairly good but IMO could use some cleanup. This takes a unix timestamp for dob because that was my requirement but could be quickly adapted to use a string:
var getAge = function(dob) {
var measureDays = function(dateObj) {
return 31*dateObj.getMonth()+dateObj.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - (measureDays(now) < measureDays(d));
}
Notice I've used a flat value of 31 in my measureDays function. All the calculation cares about is that the "day-of-year" be a monotonically increasing measure of the timestamp.
If using a javascript timestamp or string, obviously you'll want to remove the factor of 1000.

function getAge(dateString) {
var dates = dateString.split("-");
var d = new Date();
var userday = dates[0];
var usermonth = dates[1];
var useryear = dates[2];
var curday = d.getDate();
var curmonth = d.getMonth()+1;
var curyear = d.getFullYear();
var age = curyear - useryear;
if((curmonth < usermonth) || ( (curmonth == usermonth) && curday < userday )){
age--;
}
return age;
}
To get the age when european date has entered:
getAge('16-03-1989')

I've checked the examples showed before and they didn't worked in all cases, and because of this i made a script of my own. I tested this, and it works perfectly.
function getAge(birth) {
var today = new Date();
var curr_date = today.getDate();
var curr_month = today.getMonth() + 1;
var curr_year = today.getFullYear();
var pieces = birth.split('/');
var birth_date = pieces[0];
var birth_month = pieces[1];
var birth_year = pieces[2];
if (curr_month == birth_month && curr_date >= birth_date) return parseInt(curr_year-birth_year);
if (curr_month == birth_month && curr_date < birth_date) return parseInt(curr_year-birth_year-1);
if (curr_month > birth_month) return parseInt(curr_year-birth_year);
if (curr_month < birth_month) return parseInt(curr_year-birth_year-1);
}
var age = getAge('18/01/2011');
alert(age);

Get the age (years, months and days) from the date of birth with javascript
Function calcularEdad (years, months and days)
function calcularEdad(fecha) {
// Si la fecha es correcta, calculamos la edad
if (typeof fecha != "string" && fecha && esNumero(fecha.getTime())) {
fecha = formatDate(fecha, "yyyy-MM-dd");
}
var values = fecha.split("-");
var dia = values[2];
var mes = values[1];
var ano = values[0];
// cogemos los valores actuales
var fecha_hoy = new Date();
var ahora_ano = fecha_hoy.getYear();
var ahora_mes = fecha_hoy.getMonth() + 1;
var ahora_dia = fecha_hoy.getDate();
// realizamos el calculo
var edad = (ahora_ano + 1900) - ano;
if (ahora_mes < mes) {
edad--;
}
if ((mes == ahora_mes) && (ahora_dia < dia)) {
edad--;
}
if (edad > 1900) {
edad -= 1900;
}
// calculamos los meses
var meses = 0;
if (ahora_mes > mes && dia > ahora_dia)
meses = ahora_mes - mes - 1;
else if (ahora_mes > mes)
meses = ahora_mes - mes
if (ahora_mes < mes && dia < ahora_dia)
meses = 12 - (mes - ahora_mes);
else if (ahora_mes < mes)
meses = 12 - (mes - ahora_mes + 1);
if (ahora_mes == mes && dia > ahora_dia)
meses = 11;
// calculamos los dias
var dias = 0;
if (ahora_dia > dia)
dias = ahora_dia - dia;
if (ahora_dia < dia) {
ultimoDiaMes = new Date(ahora_ano, ahora_mes - 1, 0);
dias = ultimoDiaMes.getDate() - (dia - ahora_dia);
}
return edad + " años, " + meses + " meses y " + dias + " días";
}
Function esNumero
function esNumero(strNumber) {
if (strNumber == null) return false;
if (strNumber == undefined) return false;
if (typeof strNumber === "number" && !isNaN(strNumber)) return true;
if (strNumber == "") return false;
if (strNumber === "") return false;
var psInt, psFloat;
psInt = parseInt(strNumber);
psFloat = parseFloat(strNumber);
return !isNaN(strNumber) && !isNaN(psFloat);
}

One more possible solution with moment.js:
var moment = require('moment');
var startDate = new Date();
var endDate = new Date();
endDate.setDate(endDate.getFullYear() + 5); // Add 5 years to second date
console.log(moment.duration(endDate - startDate).years()); // This should returns 5

I am a bit too late but I found this to be the simplest way to calculate a birth date.
Hopefully this will help.
function init() {
writeYears("myage", 0, Age());
}
function Age() {
var birthday = new Date(1997, 02, 01), //Year, month-1 , day.
today = new Date(),
one_year = 1000 * 60 * 60 * 24 * 365;
return Math.floor((today.getTime() - birthday.getTime()) / one_year);
}
function writeYears(id, current, maximum) {
document.getElementById(id).innerHTML = current;
if (current < maximum) {
setTimeout(function() {
writeYears(id, ++current, maximum);
}, Math.sin(current / maximum) * 200);
}
}
init()
<span id="myage"></span>

Works perfect for me, guys.
getAge(birthday) {
const millis = Date.now() - Date.parse(birthday);
return new Date(millis).getFullYear() - 1970;
}

I know this is a very old thread but I wanted to put in this implementation that I wrote for finding the age which I believe is much more accurate.
var getAge = function(year,month,date){
var today = new Date();
var dob = new Date();
dob.setFullYear(year);
dob.setMonth(month-1);
dob.setDate(date);
var timeDiff = today.valueOf() - dob.valueOf();
var milliInDay = 24*60*60*1000;
var noOfDays = timeDiff / milliInDay;
var daysInYear = 365.242;
return ( noOfDays / daysInYear ) ;
}
Ofcourse you could adapt this to fit in other formats of getting the parameters. Hope this helps someone looking for a better solution.

I used this approach using logic instead of math.
It's precise and quick.
The parameters are the year, month and day of the person's birthday.
It returns the person's age as an integer.
function calculateAge(year, month, day) {
var currentDate = new Date();
var currentYear = currentDate.getFullYear();
var currentMonth = currentDate.getUTCMonth() + 1;
var currentDay = currentDate.getUTCDate();
// You need to treat the cases where the year, month or day hasn't arrived yet.
var age = currentYear - year;
if (currentMonth > month) {
return age;
} else {
if (currentDay >= day) {
return age;
} else {
age--;
return age;
}
}
}

Adopting from naveen's and original OP's posts I ended up with a reusable method stub that accepts both strings and / or JS Date objects.
I named it gregorianAge() because this calculation gives exactly how we denote age using Gregorian calendar. i.e. Not counting the end year if month and day is before the month and day of the birth year.
/**
* Calculates human age in years given a birth day. Optionally ageAtDate
* can be provided to calculate age at a specific date
*
* #param string|Date Object birthDate
* #param string|Date Object ageAtDate optional
* #returns integer Age between birthday and a given date or today
*/
function gregorianAge(birthDate, ageAtDate) {
// convert birthDate to date object if already not
if (Object.prototype.toString.call(birthDate) !== '[object Date]')
birthDate = new Date(birthDate);
// use today's date if ageAtDate is not provided
if (typeof ageAtDate == "undefined")
ageAtDate = new Date();
// convert ageAtDate to date object if already not
else if (Object.prototype.toString.call(ageAtDate) !== '[object Date]')
ageAtDate = new Date(ageAtDate);
// if conversion to date object fails return null
if (ageAtDate == null || birthDate == null)
return null;
var _m = ageAtDate.getMonth() - birthDate.getMonth();
// answer: ageAt year minus birth year less one (1) if month and day of
// ageAt year is before month and day of birth year
return (ageAtDate.getFullYear()) - birthDate.getFullYear()
- ((_m < 0 || (_m === 0 && ageAtDate.getDate() < birthDate.getDate())) ? 1 : 0)
}
// Below is for the attached snippet
function showAge() {
$('#age').text(gregorianAge($('#dob').val()))
}
$(function() {
$(".datepicker").datepicker();
showAge();
});
<link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="//code.jquery.com/jquery-1.10.2.js"></script>
<script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
DOB:
<input name="dob" value="12/31/1970" id="dob" class="datepicker" onChange="showAge()" /> AGE: <span id="age"><span>

Two more options:
// Int Age to Date as string YYY-mm-dd
function age_to_date(age)
{
try {
var d = new Date();
var new_d = '';
d.setFullYear(d.getFullYear() - Math.abs(age));
new_d = d.getFullYear() + '-' + d.getMonth() + '-' + d.getDate();
return new_d;
} catch(err) {
console.log(err.message);
}
}
// Date string (YYY-mm-dd) to Int age (years old)
function date_to_age(date)
{
try {
var today = new Date();
var d = new Date(date);
var year = today.getFullYear() - d.getFullYear();
var month = today.getMonth() - d.getMonth();
var day = today.getDate() - d.getDate();
var carry = 0;
if (year < 0)
return 0;
if (month <= 0 && day <= 0)
carry -= 1;
var age = parseInt(year);
age += carry;
return Math.abs(age);
} catch(err) {
console.log(err.message);
}
}

I've did some updated to one previous answer.
var calculateAge = function(dob) {
var days = function(date) {
return 31*date.getMonth() + date.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - ( measureDays(now) < measureDays(d));
}
I hope that helps :D

here is a simple way of calculating age:
//dob date dd/mm/yy
var d = 01/01/1990
//today
//date today string format
var today = new Date(); // i.e wed 04 may 2016 15:12:09 GMT
//todays year
var todayYear = today.getFullYear();
// today month
var todayMonth = today.getMonth();
//today date
var todayDate = today.getDate();
//dob
//dob parsed as date format
var dob = new Date(d);
// dob year
var dobYear = dob.getFullYear();
// dob month
var dobMonth = dob.getMonth();
//dob date
var dobDate = dob.getDate();
var yearsDiff = todayYear - dobYear ;
var age;
if ( todayMonth < dobMonth )
{
age = yearsDiff - 1;
}
else if ( todayMonth > dobMonth )
{
age = yearsDiff ;
}
else //if today month = dob month
{ if ( todayDate < dobDate )
{
age = yearsDiff - 1;
}
else
{
age = yearsDiff;
}
}

var now = DateTime.Now;
var age = DateTime.Now.Year - dob.Year;
if (now.Month < dob.Month || now.Month == dob.Month && now.Day < dob.Day) age--;

You may use this for age restriction in your form -
function dobvalidator(birthDateString){
strs = birthDateString.split("-");
var dd = strs[0];
var mm = strs[1];
var yy = strs[2];
var d = new Date();
var ds = d.getDate();
var ms = d.getMonth();
var ys = d.getFullYear();
var accepted_age = 18;
var days = ((accepted_age * 12) * 30) + (ms * 30) + ds;
var age = (((ys - yy) * 12) * 30) + ((12 - mm) * 30) + parseInt(30 - dd);
if((days - age) <= '0'){
console.log((days - age));
alert('You are at-least ' + accepted_age);
}else{
console.log((days - age));
alert('You are not at-least ' + accepted_age);
}
}

This is my modification:
function calculate_age(date) {
var today = new Date();
var today_month = today.getMonth() + 1; //STRANGE NUMBERING //January is 0!
var age = today.getYear() - date.getYear();
if ((today_month > date.getMonth() || ((today_month == date.getMonth()) && (today.getDate() < date.getDate())))) {
age--;
}
return age;
};

I believe that sometimes the readability is more important in this case. Unless we are validating 1000s of fields, this should be accurate and fast enough:
function is18orOlder(dateString) {
const dob = new Date(dateString);
const dobPlus18 = new Date(dob.getFullYear() + 18, dob.getMonth(), dob.getDate());
return dobPlus18 .valueOf() <= Date.now();
}
// Testing:
console.log(is18orOlder('01/01/1910')); // true
console.log(is18orOlder('01/01/2050')); // false
// When I'm posting this on 10/02/2020, so:
console.log(is18orOlder('10/08/2002')); // true
console.log(is18orOlder('10/19/2002')) // false
I like this approach instead of using a constant for how many ms are in a year, and later messing with the leap years, etc. Just letting the built-in Date to do the job.
Update, posting this snippet since one may found it useful. Since I'm enforcing a mask on the input field, to have the format of mm/dd/yyyy and already validating if the date is valid, in my case, this works too to validate 18+ years:
function is18orOlder(dateString) {
const [month, date, year] = value.split('/');
return new Date(+year + 13, +month, +date).valueOf() <= Date.now();
}

calculating age in javasctipt using 365.25 * 24 * 60 * 60 * 1000 [duplicate]

How can I calculate an age in years, given a birth date of format YYYYMMDD? Is it possible using the Date() function?
I am looking for a better solution than the one I am using now:
var dob = '19800810';
var year = Number(dob.substr(0, 4));
var month = Number(dob.substr(4, 2)) - 1;
var day = Number(dob.substr(6, 2));
var today = new Date();
var age = today.getFullYear() - year;
if (today.getMonth() < month || (today.getMonth() == month && today.getDate() < day)) {
age--;
}
alert(age);

Try this.
function getAge(dateString) {
var today = new Date();
var birthDate = new Date(dateString);
var age = today.getFullYear() - birthDate.getFullYear();
var m = today.getMonth() - birthDate.getMonth();
if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
age--;
}
return age;
}
I believe the only thing that looked crude on your code was the substr part.
Fiddle: http://jsfiddle.net/codeandcloud/n33RJ/

I would go for readability:
function _calculateAge(birthday) { // birthday is a date
var ageDifMs = Date.now() - birthday.getTime();
var ageDate = new Date(ageDifMs); // miliseconds from epoch
return Math.abs(ageDate.getUTCFullYear() - 1970);
}
Disclaimer: This also has precision issues, so this cannot be completely trusted either. It can be off by a few hours, on some years, or during daylight saving (depending on timezone).
Instead I would recommend using a library for this, if precision is very important. Also #Naveens post, is probably the most accurate, as it doesn't rely on the time of day.

Important: This answer doesn't provide an 100% accurate answer, it is off by around 10-20 hours depending on the date.
There are no better solutions ( not in these answers anyway ). - naveen
I of course couldn't resist the urge to take up the challenge and make a faster and shorter birthday calculator than the current accepted solution.
The main point for my solution, is that math is fast, so instead of using branching, and the date model javascript provides to calculate a solution we use the wonderful math
The answer looks like this, and runs ~65% faster than naveen's plus it's much shorter:
function calcAge(dateString) {
var birthday = +new Date(dateString);
return ~~((Date.now() - birthday) / (31557600000));
}
The magic number: 31557600000 is 24 * 3600 * 365.25 * 1000
Which is the length of a year, the length of a year is 365 days and 6 hours which is 0.25 day. In the end i floor the result which gives us the final age.
Here is the benchmarks: http://jsperf.com/birthday-calculation
To support OP's data format you can replace +new Date(dateString);
with +new Date(d.substr(0, 4), d.substr(4, 2)-1, d.substr(6, 2));
If you can come up with a better solution please share! :-)

Clean one-liner solution using ES6:
const getAge = birthDate => Math.floor((new Date() - new Date(birthDate).getTime()) / 3.15576e+10)
// today is 2018-06-13
getAge('1994-06-14') // 23
getAge('1994-06-13') // 24
I am using a year of 365.25 days (0.25 because of leap years) which are 3.15576e+10 milliseconds (365.25 * 24 * 60 * 60 * 1000) respectively.
It has a few hours margin so depending on the use case it may not be the best option.

With momentjs:
/* The difference, in years, between NOW and 2012-05-07 */
moment().diff(moment('20120507', 'YYYYMMDD'), 'years')

Some time ago I made a function with that purpose:
function getAge(birthDate) {
var now = new Date();
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
// days since the birthdate
var days = Math.floor((now.getTime() - birthDate.getTime())/1000/60/60/24);
var age = 0;
// iterate the years
for (var y = birthDate.getFullYear(); y <= now.getFullYear(); y++){
var daysInYear = isLeap(y) ? 366 : 365;
if (days >= daysInYear){
days -= daysInYear;
age++;
// increment the age only if there are available enough days for the year.
}
}
return age;
}
It takes a Date object as input, so you need to parse the 'YYYYMMDD' formatted date string:
var birthDateStr = '19840831',
parts = birthDateStr.match(/(\d{4})(\d{2})(\d{2})/),
dateObj = new Date(parts[1], parts[2]-1, parts[3]); // months 0-based!
getAge(dateObj); // 26

Here's my solution, just pass in a parseable date:
function getAge(birth) {
ageMS = Date.parse(Date()) - Date.parse(birth);
age = new Date();
age.setTime(ageMS);
ageYear = age.getFullYear() - 1970;
return ageYear;
// ageMonth = age.getMonth(); // Accurate calculation of the month part of the age
// ageDay = age.getDate(); // Approximate calculation of the day part of the age
}

Alternate solution, because why not:
function calculateAgeInYears (date) {
var now = new Date();
var current_year = now.getFullYear();
var year_diff = current_year - date.getFullYear();
var birthday_this_year = new Date(current_year, date.getMonth(), date.getDate());
var has_had_birthday_this_year = (now >= birthday_this_year);
return has_had_birthday_this_year
? year_diff
: year_diff - 1;
}

function age()
{
var birthdate = $j('#birthDate').val(); // in "mm/dd/yyyy" format
var senddate = $j('#expireDate').val(); // in "mm/dd/yyyy" format
var x = birthdate.split("/");
var y = senddate.split("/");
var bdays = x[1];
var bmonths = x[0];
var byear = x[2];
//alert(bdays);
var sdays = y[1];
var smonths = y[0];
var syear = y[2];
//alert(sdays);
if(sdays < bdays)
{
sdays = parseInt(sdays) + 30;
smonths = parseInt(smonths) - 1;
//alert(sdays);
var fdays = sdays - bdays;
//alert(fdays);
}
else{
var fdays = sdays - bdays;
}
if(smonths < bmonths)
{
smonths = parseInt(smonths) + 12;
syear = syear - 1;
var fmonths = smonths - bmonths;
}
else
{
var fmonths = smonths - bmonths;
}
var fyear = syear - byear;
document.getElementById('patientAge').value = fyear+' years '+fmonths+' months '+fdays+' days';
}

I think that could be simply like that:
function age(dateString){
let birth = new Date(dateString);
let now = new Date();
let beforeBirth = ((() => {birth.setDate(now.getDate());birth.setMonth(now.getMonth()); return birth.getTime()})() < birth.getTime()) ? 0 : 1;
return now.getFullYear() - birth.getFullYear() - beforeBirth;
}
age('09/20/1981');
//35
Works also with a timestamp
age(403501000000)
//34

That's the most elegant way for me:
const getAge = (birthDateString) => {
const today = new Date();
const birthDate = new Date(birthDateString);
const yearsDifference = today.getFullYear() - birthDate.getFullYear();
if (
today.getMonth() < birthDate.getMonth() ||
(today.getMonth() === birthDate.getMonth() && today.getDate() < birthDate.getDate())
) {
return yearsDifference - 1;
}
return yearsDifference;
};
console.log(getAge('2018-03-12'));

This question is over 10 years old an nobody has addressed the prompt that they already have the birth date in YYYYMMDD format?
If you have a past date and the current date both in YYYYMMDD format, you can very quickly calculate the number of years between them like this:
var pastDate = '20101030';
var currentDate = '20210622';
var years = Math.floor( ( currentDate - pastDate ) * 0.0001 );
// 10 (10.9592)
You can get the current date formatted as YYYYMMDD like this:
var now = new Date();
var currentDate = [
now.getFullYear(),
('0' + (now.getMonth() + 1) ).slice(-2),
('0' + now.getDate() ).slice(-2),
].join('');

To test whether the birthday already passed or not, I define a helper function Date.prototype.getDoY, which effectively returns the day number of the year. The rest is pretty self-explanatory.
Date.prototype.getDoY = function() {
var onejan = new Date(this.getFullYear(), 0, 1);
return Math.floor(((this - onejan) / 86400000) + 1);
};
function getAge(birthDate) {
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
var now = new Date(),
age = now.getFullYear() - birthDate.getFullYear(),
doyNow = now.getDoY(),
doyBirth = birthDate.getDoY();
// normalize day-of-year in leap years
if (isLeap(now.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyNow--;
if (isLeap(birthDate.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyBirth--;
if (doyNow <= doyBirth)
age--; // birthday not yet passed this year, so -1
return age;
};
var myBirth = new Date(2001, 6, 4);
console.log(getAge(myBirth));

I just had to write this function for myself - the accepted answer is fairly good but IMO could use some cleanup. This takes a unix timestamp for dob because that was my requirement but could be quickly adapted to use a string:
var getAge = function(dob) {
var measureDays = function(dateObj) {
return 31*dateObj.getMonth()+dateObj.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - (measureDays(now) < measureDays(d));
}
Notice I've used a flat value of 31 in my measureDays function. All the calculation cares about is that the "day-of-year" be a monotonically increasing measure of the timestamp.
If using a javascript timestamp or string, obviously you'll want to remove the factor of 1000.

function getAge(dateString) {
var dates = dateString.split("-");
var d = new Date();
var userday = dates[0];
var usermonth = dates[1];
var useryear = dates[2];
var curday = d.getDate();
var curmonth = d.getMonth()+1;
var curyear = d.getFullYear();
var age = curyear - useryear;
if((curmonth < usermonth) || ( (curmonth == usermonth) && curday < userday )){
age--;
}
return age;
}
To get the age when european date has entered:
getAge('16-03-1989')

I've checked the examples showed before and they didn't worked in all cases, and because of this i made a script of my own. I tested this, and it works perfectly.
function getAge(birth) {
var today = new Date();
var curr_date = today.getDate();
var curr_month = today.getMonth() + 1;
var curr_year = today.getFullYear();
var pieces = birth.split('/');
var birth_date = pieces[0];
var birth_month = pieces[1];
var birth_year = pieces[2];
if (curr_month == birth_month && curr_date >= birth_date) return parseInt(curr_year-birth_year);
if (curr_month == birth_month && curr_date < birth_date) return parseInt(curr_year-birth_year-1);
if (curr_month > birth_month) return parseInt(curr_year-birth_year);
if (curr_month < birth_month) return parseInt(curr_year-birth_year-1);
}
var age = getAge('18/01/2011');
alert(age);

Get the age (years, months and days) from the date of birth with javascript
Function calcularEdad (years, months and days)
function calcularEdad(fecha) {
// Si la fecha es correcta, calculamos la edad
if (typeof fecha != "string" && fecha && esNumero(fecha.getTime())) {
fecha = formatDate(fecha, "yyyy-MM-dd");
}
var values = fecha.split("-");
var dia = values[2];
var mes = values[1];
var ano = values[0];
// cogemos los valores actuales
var fecha_hoy = new Date();
var ahora_ano = fecha_hoy.getYear();
var ahora_mes = fecha_hoy.getMonth() + 1;
var ahora_dia = fecha_hoy.getDate();
// realizamos el calculo
var edad = (ahora_ano + 1900) - ano;
if (ahora_mes < mes) {
edad--;
}
if ((mes == ahora_mes) && (ahora_dia < dia)) {
edad--;
}
if (edad > 1900) {
edad -= 1900;
}
// calculamos los meses
var meses = 0;
if (ahora_mes > mes && dia > ahora_dia)
meses = ahora_mes - mes - 1;
else if (ahora_mes > mes)
meses = ahora_mes - mes
if (ahora_mes < mes && dia < ahora_dia)
meses = 12 - (mes - ahora_mes);
else if (ahora_mes < mes)
meses = 12 - (mes - ahora_mes + 1);
if (ahora_mes == mes && dia > ahora_dia)
meses = 11;
// calculamos los dias
var dias = 0;
if (ahora_dia > dia)
dias = ahora_dia - dia;
if (ahora_dia < dia) {
ultimoDiaMes = new Date(ahora_ano, ahora_mes - 1, 0);
dias = ultimoDiaMes.getDate() - (dia - ahora_dia);
}
return edad + " años, " + meses + " meses y " + dias + " días";
}
Function esNumero
function esNumero(strNumber) {
if (strNumber == null) return false;
if (strNumber == undefined) return false;
if (typeof strNumber === "number" && !isNaN(strNumber)) return true;
if (strNumber == "") return false;
if (strNumber === "") return false;
var psInt, psFloat;
psInt = parseInt(strNumber);
psFloat = parseFloat(strNumber);
return !isNaN(strNumber) && !isNaN(psFloat);
}

One more possible solution with moment.js:
var moment = require('moment');
var startDate = new Date();
var endDate = new Date();
endDate.setDate(endDate.getFullYear() + 5); // Add 5 years to second date
console.log(moment.duration(endDate - startDate).years()); // This should returns 5

I am a bit too late but I found this to be the simplest way to calculate a birth date.
Hopefully this will help.
function init() {
writeYears("myage", 0, Age());
}
function Age() {
var birthday = new Date(1997, 02, 01), //Year, month-1 , day.
today = new Date(),
one_year = 1000 * 60 * 60 * 24 * 365;
return Math.floor((today.getTime() - birthday.getTime()) / one_year);
}
function writeYears(id, current, maximum) {
document.getElementById(id).innerHTML = current;
if (current < maximum) {
setTimeout(function() {
writeYears(id, ++current, maximum);
}, Math.sin(current / maximum) * 200);
}
}
init()
<span id="myage"></span>

Works perfect for me, guys.
getAge(birthday) {
const millis = Date.now() - Date.parse(birthday);
return new Date(millis).getFullYear() - 1970;
}

I know this is a very old thread but I wanted to put in this implementation that I wrote for finding the age which I believe is much more accurate.
var getAge = function(year,month,date){
var today = new Date();
var dob = new Date();
dob.setFullYear(year);
dob.setMonth(month-1);
dob.setDate(date);
var timeDiff = today.valueOf() - dob.valueOf();
var milliInDay = 24*60*60*1000;
var noOfDays = timeDiff / milliInDay;
var daysInYear = 365.242;
return ( noOfDays / daysInYear ) ;
}
Ofcourse you could adapt this to fit in other formats of getting the parameters. Hope this helps someone looking for a better solution.

I used this approach using logic instead of math.
It's precise and quick.
The parameters are the year, month and day of the person's birthday.
It returns the person's age as an integer.
function calculateAge(year, month, day) {
var currentDate = new Date();
var currentYear = currentDate.getFullYear();
var currentMonth = currentDate.getUTCMonth() + 1;
var currentDay = currentDate.getUTCDate();
// You need to treat the cases where the year, month or day hasn't arrived yet.
var age = currentYear - year;
if (currentMonth > month) {
return age;
} else {
if (currentDay >= day) {
return age;
} else {
age--;
return age;
}
}
}

Adopting from naveen's and original OP's posts I ended up with a reusable method stub that accepts both strings and / or JS Date objects.
I named it gregorianAge() because this calculation gives exactly how we denote age using Gregorian calendar. i.e. Not counting the end year if month and day is before the month and day of the birth year.
/**
* Calculates human age in years given a birth day. Optionally ageAtDate
* can be provided to calculate age at a specific date
*
* #param string|Date Object birthDate
* #param string|Date Object ageAtDate optional
* #returns integer Age between birthday and a given date or today
*/
function gregorianAge(birthDate, ageAtDate) {
// convert birthDate to date object if already not
if (Object.prototype.toString.call(birthDate) !== '[object Date]')
birthDate = new Date(birthDate);
// use today's date if ageAtDate is not provided
if (typeof ageAtDate == "undefined")
ageAtDate = new Date();
// convert ageAtDate to date object if already not
else if (Object.prototype.toString.call(ageAtDate) !== '[object Date]')
ageAtDate = new Date(ageAtDate);
// if conversion to date object fails return null
if (ageAtDate == null || birthDate == null)
return null;
var _m = ageAtDate.getMonth() - birthDate.getMonth();
// answer: ageAt year minus birth year less one (1) if month and day of
// ageAt year is before month and day of birth year
return (ageAtDate.getFullYear()) - birthDate.getFullYear()
- ((_m < 0 || (_m === 0 && ageAtDate.getDate() < birthDate.getDate())) ? 1 : 0)
}
// Below is for the attached snippet
function showAge() {
$('#age').text(gregorianAge($('#dob').val()))
}
$(function() {
$(".datepicker").datepicker();
showAge();
});
<link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="//code.jquery.com/jquery-1.10.2.js"></script>
<script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
DOB:
<input name="dob" value="12/31/1970" id="dob" class="datepicker" onChange="showAge()" /> AGE: <span id="age"><span>

Two more options:
// Int Age to Date as string YYY-mm-dd
function age_to_date(age)
{
try {
var d = new Date();
var new_d = '';
d.setFullYear(d.getFullYear() - Math.abs(age));
new_d = d.getFullYear() + '-' + d.getMonth() + '-' + d.getDate();
return new_d;
} catch(err) {
console.log(err.message);
}
}
// Date string (YYY-mm-dd) to Int age (years old)
function date_to_age(date)
{
try {
var today = new Date();
var d = new Date(date);
var year = today.getFullYear() - d.getFullYear();
var month = today.getMonth() - d.getMonth();
var day = today.getDate() - d.getDate();
var carry = 0;
if (year < 0)
return 0;
if (month <= 0 && day <= 0)
carry -= 1;
var age = parseInt(year);
age += carry;
return Math.abs(age);
} catch(err) {
console.log(err.message);
}
}

I've did some updated to one previous answer.
var calculateAge = function(dob) {
var days = function(date) {
return 31*date.getMonth() + date.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - ( measureDays(now) < measureDays(d));
}
I hope that helps :D

here is a simple way of calculating age:
//dob date dd/mm/yy
var d = 01/01/1990
//today
//date today string format
var today = new Date(); // i.e wed 04 may 2016 15:12:09 GMT
//todays year
var todayYear = today.getFullYear();
// today month
var todayMonth = today.getMonth();
//today date
var todayDate = today.getDate();
//dob
//dob parsed as date format
var dob = new Date(d);
// dob year
var dobYear = dob.getFullYear();
// dob month
var dobMonth = dob.getMonth();
//dob date
var dobDate = dob.getDate();
var yearsDiff = todayYear - dobYear ;
var age;
if ( todayMonth < dobMonth )
{
age = yearsDiff - 1;
}
else if ( todayMonth > dobMonth )
{
age = yearsDiff ;
}
else //if today month = dob month
{ if ( todayDate < dobDate )
{
age = yearsDiff - 1;
}
else
{
age = yearsDiff;
}
}

var now = DateTime.Now;
var age = DateTime.Now.Year - dob.Year;
if (now.Month < dob.Month || now.Month == dob.Month && now.Day < dob.Day) age--;

You may use this for age restriction in your form -
function dobvalidator(birthDateString){
strs = birthDateString.split("-");
var dd = strs[0];
var mm = strs[1];
var yy = strs[2];
var d = new Date();
var ds = d.getDate();
var ms = d.getMonth();
var ys = d.getFullYear();
var accepted_age = 18;
var days = ((accepted_age * 12) * 30) + (ms * 30) + ds;
var age = (((ys - yy) * 12) * 30) + ((12 - mm) * 30) + parseInt(30 - dd);
if((days - age) <= '0'){
console.log((days - age));
alert('You are at-least ' + accepted_age);
}else{
console.log((days - age));
alert('You are not at-least ' + accepted_age);
}
}

This is my modification:
function calculate_age(date) {
var today = new Date();
var today_month = today.getMonth() + 1; //STRANGE NUMBERING //January is 0!
var age = today.getYear() - date.getYear();
if ((today_month > date.getMonth() || ((today_month == date.getMonth()) && (today.getDate() < date.getDate())))) {
age--;
}
return age;
};

I believe that sometimes the readability is more important in this case. Unless we are validating 1000s of fields, this should be accurate and fast enough:
function is18orOlder(dateString) {
const dob = new Date(dateString);
const dobPlus18 = new Date(dob.getFullYear() + 18, dob.getMonth(), dob.getDate());
return dobPlus18 .valueOf() <= Date.now();
}
// Testing:
console.log(is18orOlder('01/01/1910')); // true
console.log(is18orOlder('01/01/2050')); // false
// When I'm posting this on 10/02/2020, so:
console.log(is18orOlder('10/08/2002')); // true
console.log(is18orOlder('10/19/2002')) // false
I like this approach instead of using a constant for how many ms are in a year, and later messing with the leap years, etc. Just letting the built-in Date to do the job.
Update, posting this snippet since one may found it useful. Since I'm enforcing a mask on the input field, to have the format of mm/dd/yyyy and already validating if the date is valid, in my case, this works too to validate 18+ years:
function is18orOlder(dateString) {
const [month, date, year] = value.split('/');
return new Date(+year + 13, +month, +date).valueOf() <= Date.now();
}

Calculate days remaining until next birthday in Javascript

I'm trying to calculate remaining days until the next birthday but keeps running into problems. This is the code so far (has some issues with negative days if your birthday has already been this year etc). Any tips on how I can solve this?
var birthdayDate = new Date(year, month-1, day, 12);
var now = new Date();
var days = 0;
Math.floor(days = ( (birthdayDate.getTime() - now.getTime()) / (1000*60*60*24)));
if(days < 0)
{
var yearDiff = birthdayDate.getYear() - now.getYear();
yearDiff *= -1;
var monthDiff = birthdayDate.getMonth() - now.getMonth();
var daysDiff = birthdayDate.getDay() - now.getDay();
if(monthDiff <= 0)
{
if(daysDiff > 0)
{
}
else
{
days += 365;
}
}
var extraDays = yearDiff / 4;
days = days + (yearDiff * 365) + extraDays;
}
else
{
throw new FutureDateException();
}
days = Math.floor(Math.round(days));
if(days === 365)
{
days = 0;
}
if(days === 366)
{
days = 1;
}
return days;

I'd do something like this:
var myBirthday, today, bday, diff, days;
myBirthday = [6,2]; // 6th of February
today = new Date();
bday = new Date(today.getFullYear(),myBirthday[1]-1,myBirthday[0]);
if( today.getTime() > bday.getTime()) {
bday.setFullYear(bday.getFullYear()+1);
}
diff = bday.getTime()-today.getTime();
days = Math.floor(diff/(1000*60*60*24));
alert(days+" days until Niet's birthday!");

To return the correct number of days,
regardless of daylight savings time use Math.round rather than Math.floor,
and set both dates time to midnight.
function daysUntilNext(month, day){
var tday= new Date(), y= tday.getFullYear(), next= new Date(y, month-1, day);
tday.setHours(0, 0, 0, 0);
if(tday>next) next.setFullYear(y+1);
return Math.round((next-tday)/8.64e7);
}
//test 1
var d= daysUntilNext(12, 25);
if(d=== 0) alert('Merry Christmas!');
else alert(d+' day'+(d>1? 's': '')+' until Christmas');
//test2
var d= daysUntilNext(4, 26);
if(d=== 0) alert('Happy Birthday!');
else alert(d+' day'+(d>1? 's': '')+' until your birthday');

// Your birthday
var birthday = new Date(1985, 0, 1);
var today = new Date();
//Set current year or the next year if you already had birthday this year
birthday.setFullYear(today.getFullYear());
if (today > birthday) {
birthday.setFullYear(today.getFullYear() + 1);
}
//Calculate difference between days
Math.floor((birthday - today) / (1000*60*60*24))
For any date calculations in JS, I suggest using date.js library. JS has very strange date/time concepts :)

vijay birthday calculate in days
function thalapathyBirthday(month, day) {
var manos = new Date(),
vijay = manos.getFullYear(),
next = new Date(vijay, month - 1, day);
manos.setHours(0, 0, 0, 0);
if (manos > next) next.setFullYear(vijay + 1);
return Math.round((next - manos) / 8.64e7);
}
var vajasan = thalapathyBirthday(06, 22);
if (vajasan === 0) console.log('Happy Birthday Thalapathy!');
else console.log(vajasan + ' day' + (vajasan > 1 ? 's' : '') + ' to go thalapathy birthday');

Calculate age depending upon current date & birth Date [duplicate]

How can I calculate an age in years, given a birth date of format YYYYMMDD? Is it possible using the Date() function?
I am looking for a better solution than the one I am using now:
var dob = '19800810';
var year = Number(dob.substr(0, 4));
var month = Number(dob.substr(4, 2)) - 1;
var day = Number(dob.substr(6, 2));
var today = new Date();
var age = today.getFullYear() - year;
if (today.getMonth() < month || (today.getMonth() == month && today.getDate() < day)) {
age--;
}
alert(age);

Try this.
function getAge(dateString) {
var today = new Date();
var birthDate = new Date(dateString);
var age = today.getFullYear() - birthDate.getFullYear();
var m = today.getMonth() - birthDate.getMonth();
if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
age--;
}
return age;
}
I believe the only thing that looked crude on your code was the substr part.
Fiddle: http://jsfiddle.net/codeandcloud/n33RJ/

I would go for readability:
function _calculateAge(birthday) { // birthday is a date
var ageDifMs = Date.now() - birthday.getTime();
var ageDate = new Date(ageDifMs); // miliseconds from epoch
return Math.abs(ageDate.getUTCFullYear() - 1970);
}
Disclaimer: This also has precision issues, so this cannot be completely trusted either. It can be off by a few hours, on some years, or during daylight saving (depending on timezone).
Instead I would recommend using a library for this, if precision is very important. Also #Naveens post, is probably the most accurate, as it doesn't rely on the time of day.

Important: This answer doesn't provide an 100% accurate answer, it is off by around 10-20 hours depending on the date.
There are no better solutions ( not in these answers anyway ). - naveen
I of course couldn't resist the urge to take up the challenge and make a faster and shorter birthday calculator than the current accepted solution.
The main point for my solution, is that math is fast, so instead of using branching, and the date model javascript provides to calculate a solution we use the wonderful math
The answer looks like this, and runs ~65% faster than naveen's plus it's much shorter:
function calcAge(dateString) {
var birthday = +new Date(dateString);
return ~~((Date.now() - birthday) / (31557600000));
}
The magic number: 31557600000 is 24 * 3600 * 365.25 * 1000
Which is the length of a year, the length of a year is 365 days and 6 hours which is 0.25 day. In the end i floor the result which gives us the final age.
Here is the benchmarks: http://jsperf.com/birthday-calculation
To support OP's data format you can replace +new Date(dateString);
with +new Date(d.substr(0, 4), d.substr(4, 2)-1, d.substr(6, 2));
If you can come up with a better solution please share! :-)

Clean one-liner solution using ES6:
const getAge = birthDate => Math.floor((new Date() - new Date(birthDate).getTime()) / 3.15576e+10)
// today is 2018-06-13
getAge('1994-06-14') // 23
getAge('1994-06-13') // 24
I am using a year of 365.25 days (0.25 because of leap years) which are 3.15576e+10 milliseconds (365.25 * 24 * 60 * 60 * 1000) respectively.
It has a few hours margin so depending on the use case it may not be the best option.

With momentjs:
/* The difference, in years, between NOW and 2012-05-07 */
moment().diff(moment('20120507', 'YYYYMMDD'), 'years')

Some time ago I made a function with that purpose:
function getAge(birthDate) {
var now = new Date();
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
// days since the birthdate
var days = Math.floor((now.getTime() - birthDate.getTime())/1000/60/60/24);
var age = 0;
// iterate the years
for (var y = birthDate.getFullYear(); y <= now.getFullYear(); y++){
var daysInYear = isLeap(y) ? 366 : 365;
if (days >= daysInYear){
days -= daysInYear;
age++;
// increment the age only if there are available enough days for the year.
}
}
return age;
}
It takes a Date object as input, so you need to parse the 'YYYYMMDD' formatted date string:
var birthDateStr = '19840831',
parts = birthDateStr.match(/(\d{4})(\d{2})(\d{2})/),
dateObj = new Date(parts[1], parts[2]-1, parts[3]); // months 0-based!
getAge(dateObj); // 26

Here's my solution, just pass in a parseable date:
function getAge(birth) {
ageMS = Date.parse(Date()) - Date.parse(birth);
age = new Date();
age.setTime(ageMS);
ageYear = age.getFullYear() - 1970;
return ageYear;
// ageMonth = age.getMonth(); // Accurate calculation of the month part of the age
// ageDay = age.getDate(); // Approximate calculation of the day part of the age
}

Alternate solution, because why not:
function calculateAgeInYears (date) {
var now = new Date();
var current_year = now.getFullYear();
var year_diff = current_year - date.getFullYear();
var birthday_this_year = new Date(current_year, date.getMonth(), date.getDate());
var has_had_birthday_this_year = (now >= birthday_this_year);
return has_had_birthday_this_year
? year_diff
: year_diff - 1;
}

function age()
{
var birthdate = $j('#birthDate').val(); // in "mm/dd/yyyy" format
var senddate = $j('#expireDate').val(); // in "mm/dd/yyyy" format
var x = birthdate.split("/");
var y = senddate.split("/");
var bdays = x[1];
var bmonths = x[0];
var byear = x[2];
//alert(bdays);
var sdays = y[1];
var smonths = y[0];
var syear = y[2];
//alert(sdays);
if(sdays < bdays)
{
sdays = parseInt(sdays) + 30;
smonths = parseInt(smonths) - 1;
//alert(sdays);
var fdays = sdays - bdays;
//alert(fdays);
}
else{
var fdays = sdays - bdays;
}
if(smonths < bmonths)
{
smonths = parseInt(smonths) + 12;
syear = syear - 1;
var fmonths = smonths - bmonths;
}
else
{
var fmonths = smonths - bmonths;
}
var fyear = syear - byear;
document.getElementById('patientAge').value = fyear+' years '+fmonths+' months '+fdays+' days';
}

I think that could be simply like that:
function age(dateString){
let birth = new Date(dateString);
let now = new Date();
let beforeBirth = ((() => {birth.setDate(now.getDate());birth.setMonth(now.getMonth()); return birth.getTime()})() < birth.getTime()) ? 0 : 1;
return now.getFullYear() - birth.getFullYear() - beforeBirth;
}
age('09/20/1981');
//35
Works also with a timestamp
age(403501000000)
//34

That's the most elegant way for me:
const getAge = (birthDateString) => {
const today = new Date();
const birthDate = new Date(birthDateString);
const yearsDifference = today.getFullYear() - birthDate.getFullYear();
if (
today.getMonth() < birthDate.getMonth() ||
(today.getMonth() === birthDate.getMonth() && today.getDate() < birthDate.getDate())
) {
return yearsDifference - 1;
}
return yearsDifference;
};
console.log(getAge('2018-03-12'));

This question is over 10 years old an nobody has addressed the prompt that they already have the birth date in YYYYMMDD format?
If you have a past date and the current date both in YYYYMMDD format, you can very quickly calculate the number of years between them like this:
var pastDate = '20101030';
var currentDate = '20210622';
var years = Math.floor( ( currentDate - pastDate ) * 0.0001 );
// 10 (10.9592)
You can get the current date formatted as YYYYMMDD like this:
var now = new Date();
var currentDate = [
now.getFullYear(),
('0' + (now.getMonth() + 1) ).slice(-2),
('0' + now.getDate() ).slice(-2),
].join('');

To test whether the birthday already passed or not, I define a helper function Date.prototype.getDoY, which effectively returns the day number of the year. The rest is pretty self-explanatory.
Date.prototype.getDoY = function() {
var onejan = new Date(this.getFullYear(), 0, 1);
return Math.floor(((this - onejan) / 86400000) + 1);
};
function getAge(birthDate) {
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
var now = new Date(),
age = now.getFullYear() - birthDate.getFullYear(),
doyNow = now.getDoY(),
doyBirth = birthDate.getDoY();
// normalize day-of-year in leap years
if (isLeap(now.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyNow--;
if (isLeap(birthDate.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyBirth--;
if (doyNow <= doyBirth)
age--; // birthday not yet passed this year, so -1
return age;
};
var myBirth = new Date(2001, 6, 4);
console.log(getAge(myBirth));

I just had to write this function for myself - the accepted answer is fairly good but IMO could use some cleanup. This takes a unix timestamp for dob because that was my requirement but could be quickly adapted to use a string:
var getAge = function(dob) {
var measureDays = function(dateObj) {
return 31*dateObj.getMonth()+dateObj.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - (measureDays(now) < measureDays(d));
}
Notice I've used a flat value of 31 in my measureDays function. All the calculation cares about is that the "day-of-year" be a monotonically increasing measure of the timestamp.
If using a javascript timestamp or string, obviously you'll want to remove the factor of 1000.

function getAge(dateString) {
var dates = dateString.split("-");
var d = new Date();
var userday = dates[0];
var usermonth = dates[1];
var useryear = dates[2];
var curday = d.getDate();
var curmonth = d.getMonth()+1;
var curyear = d.getFullYear();
var age = curyear - useryear;
if((curmonth < usermonth) || ( (curmonth == usermonth) && curday < userday )){
age--;
}
return age;
}
To get the age when european date has entered:
getAge('16-03-1989')

I've checked the examples showed before and they didn't worked in all cases, and because of this i made a script of my own. I tested this, and it works perfectly.
function getAge(birth) {
var today = new Date();
var curr_date = today.getDate();
var curr_month = today.getMonth() + 1;
var curr_year = today.getFullYear();
var pieces = birth.split('/');
var birth_date = pieces[0];
var birth_month = pieces[1];
var birth_year = pieces[2];
if (curr_month == birth_month && curr_date >= birth_date) return parseInt(curr_year-birth_year);
if (curr_month == birth_month && curr_date < birth_date) return parseInt(curr_year-birth_year-1);
if (curr_month > birth_month) return parseInt(curr_year-birth_year);
if (curr_month < birth_month) return parseInt(curr_year-birth_year-1);
}
var age = getAge('18/01/2011');
alert(age);

Get the age (years, months and days) from the date of birth with javascript
Function calcularEdad (years, months and days)
function calcularEdad(fecha) {
// Si la fecha es correcta, calculamos la edad
if (typeof fecha != "string" && fecha && esNumero(fecha.getTime())) {
fecha = formatDate(fecha, "yyyy-MM-dd");
}
var values = fecha.split("-");
var dia = values[2];
var mes = values[1];
var ano = values[0];
// cogemos los valores actuales
var fecha_hoy = new Date();
var ahora_ano = fecha_hoy.getYear();
var ahora_mes = fecha_hoy.getMonth() + 1;
var ahora_dia = fecha_hoy.getDate();
// realizamos el calculo
var edad = (ahora_ano + 1900) - ano;
if (ahora_mes < mes) {
edad--;
}
if ((mes == ahora_mes) && (ahora_dia < dia)) {
edad--;
}
if (edad > 1900) {
edad -= 1900;
}
// calculamos los meses
var meses = 0;
if (ahora_mes > mes && dia > ahora_dia)
meses = ahora_mes - mes - 1;
else if (ahora_mes > mes)
meses = ahora_mes - mes
if (ahora_mes < mes && dia < ahora_dia)
meses = 12 - (mes - ahora_mes);
else if (ahora_mes < mes)
meses = 12 - (mes - ahora_mes + 1);
if (ahora_mes == mes && dia > ahora_dia)
meses = 11;
// calculamos los dias
var dias = 0;
if (ahora_dia > dia)
dias = ahora_dia - dia;
if (ahora_dia < dia) {
ultimoDiaMes = new Date(ahora_ano, ahora_mes - 1, 0);
dias = ultimoDiaMes.getDate() - (dia - ahora_dia);
}
return edad + " años, " + meses + " meses y " + dias + " días";
}
Function esNumero
function esNumero(strNumber) {
if (strNumber == null) return false;
if (strNumber == undefined) return false;
if (typeof strNumber === "number" && !isNaN(strNumber)) return true;
if (strNumber == "") return false;
if (strNumber === "") return false;
var psInt, psFloat;
psInt = parseInt(strNumber);
psFloat = parseFloat(strNumber);
return !isNaN(strNumber) && !isNaN(psFloat);
}

One more possible solution with moment.js:
var moment = require('moment');
var startDate = new Date();
var endDate = new Date();
endDate.setDate(endDate.getFullYear() + 5); // Add 5 years to second date
console.log(moment.duration(endDate - startDate).years()); // This should returns 5

I am a bit too late but I found this to be the simplest way to calculate a birth date.
Hopefully this will help.
function init() {
writeYears("myage", 0, Age());
}
function Age() {
var birthday = new Date(1997, 02, 01), //Year, month-1 , day.
today = new Date(),
one_year = 1000 * 60 * 60 * 24 * 365;
return Math.floor((today.getTime() - birthday.getTime()) / one_year);
}
function writeYears(id, current, maximum) {
document.getElementById(id).innerHTML = current;
if (current < maximum) {
setTimeout(function() {
writeYears(id, ++current, maximum);
}, Math.sin(current / maximum) * 200);
}
}
init()
<span id="myage"></span>

Works perfect for me, guys.
getAge(birthday) {
const millis = Date.now() - Date.parse(birthday);
return new Date(millis).getFullYear() - 1970;
}

I know this is a very old thread but I wanted to put in this implementation that I wrote for finding the age which I believe is much more accurate.
var getAge = function(year,month,date){
var today = new Date();
var dob = new Date();
dob.setFullYear(year);
dob.setMonth(month-1);
dob.setDate(date);
var timeDiff = today.valueOf() - dob.valueOf();
var milliInDay = 24*60*60*1000;
var noOfDays = timeDiff / milliInDay;
var daysInYear = 365.242;
return ( noOfDays / daysInYear ) ;
}
Ofcourse you could adapt this to fit in other formats of getting the parameters. Hope this helps someone looking for a better solution.

I used this approach using logic instead of math.
It's precise and quick.
The parameters are the year, month and day of the person's birthday.
It returns the person's age as an integer.
function calculateAge(year, month, day) {
var currentDate = new Date();
var currentYear = currentDate.getFullYear();
var currentMonth = currentDate.getUTCMonth() + 1;
var currentDay = currentDate.getUTCDate();
// You need to treat the cases where the year, month or day hasn't arrived yet.
var age = currentYear - year;
if (currentMonth > month) {
return age;
} else {
if (currentDay >= day) {
return age;
} else {
age--;
return age;
}
}
}

Adopting from naveen's and original OP's posts I ended up with a reusable method stub that accepts both strings and / or JS Date objects.
I named it gregorianAge() because this calculation gives exactly how we denote age using Gregorian calendar. i.e. Not counting the end year if month and day is before the month and day of the birth year.
/**
* Calculates human age in years given a birth day. Optionally ageAtDate
* can be provided to calculate age at a specific date
*
* #param string|Date Object birthDate
* #param string|Date Object ageAtDate optional
* #returns integer Age between birthday and a given date or today
*/
function gregorianAge(birthDate, ageAtDate) {
// convert birthDate to date object if already not
if (Object.prototype.toString.call(birthDate) !== '[object Date]')
birthDate = new Date(birthDate);
// use today's date if ageAtDate is not provided
if (typeof ageAtDate == "undefined")
ageAtDate = new Date();
// convert ageAtDate to date object if already not
else if (Object.prototype.toString.call(ageAtDate) !== '[object Date]')
ageAtDate = new Date(ageAtDate);
// if conversion to date object fails return null
if (ageAtDate == null || birthDate == null)
return null;
var _m = ageAtDate.getMonth() - birthDate.getMonth();
// answer: ageAt year minus birth year less one (1) if month and day of
// ageAt year is before month and day of birth year
return (ageAtDate.getFullYear()) - birthDate.getFullYear()
- ((_m < 0 || (_m === 0 && ageAtDate.getDate() < birthDate.getDate())) ? 1 : 0)
}
// Below is for the attached snippet
function showAge() {
$('#age').text(gregorianAge($('#dob').val()))
}
$(function() {
$(".datepicker").datepicker();
showAge();
});
<link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="//code.jquery.com/jquery-1.10.2.js"></script>
<script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
DOB:
<input name="dob" value="12/31/1970" id="dob" class="datepicker" onChange="showAge()" /> AGE: <span id="age"><span>

Two more options:
// Int Age to Date as string YYY-mm-dd
function age_to_date(age)
{
try {
var d = new Date();
var new_d = '';
d.setFullYear(d.getFullYear() - Math.abs(age));
new_d = d.getFullYear() + '-' + d.getMonth() + '-' + d.getDate();
return new_d;
} catch(err) {
console.log(err.message);
}
}
// Date string (YYY-mm-dd) to Int age (years old)
function date_to_age(date)
{
try {
var today = new Date();
var d = new Date(date);
var year = today.getFullYear() - d.getFullYear();
var month = today.getMonth() - d.getMonth();
var day = today.getDate() - d.getDate();
var carry = 0;
if (year < 0)
return 0;
if (month <= 0 && day <= 0)
carry -= 1;
var age = parseInt(year);
age += carry;
return Math.abs(age);
} catch(err) {
console.log(err.message);
}
}

I've did some updated to one previous answer.
var calculateAge = function(dob) {
var days = function(date) {
return 31*date.getMonth() + date.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - ( measureDays(now) < measureDays(d));
}
I hope that helps :D

here is a simple way of calculating age:
//dob date dd/mm/yy
var d = 01/01/1990
//today
//date today string format
var today = new Date(); // i.e wed 04 may 2016 15:12:09 GMT
//todays year
var todayYear = today.getFullYear();
// today month
var todayMonth = today.getMonth();
//today date
var todayDate = today.getDate();
//dob
//dob parsed as date format
var dob = new Date(d);
// dob year
var dobYear = dob.getFullYear();
// dob month
var dobMonth = dob.getMonth();
//dob date
var dobDate = dob.getDate();
var yearsDiff = todayYear - dobYear ;
var age;
if ( todayMonth < dobMonth )
{
age = yearsDiff - 1;
}
else if ( todayMonth > dobMonth )
{
age = yearsDiff ;
}
else //if today month = dob month
{ if ( todayDate < dobDate )
{
age = yearsDiff - 1;
}
else
{
age = yearsDiff;
}
}

var now = DateTime.Now;
var age = DateTime.Now.Year - dob.Year;
if (now.Month < dob.Month || now.Month == dob.Month && now.Day < dob.Day) age--;

You may use this for age restriction in your form -
function dobvalidator(birthDateString){
strs = birthDateString.split("-");
var dd = strs[0];
var mm = strs[1];
var yy = strs[2];
var d = new Date();
var ds = d.getDate();
var ms = d.getMonth();
var ys = d.getFullYear();
var accepted_age = 18;
var days = ((accepted_age * 12) * 30) + (ms * 30) + ds;
var age = (((ys - yy) * 12) * 30) + ((12 - mm) * 30) + parseInt(30 - dd);
if((days - age) <= '0'){
console.log((days - age));
alert('You are at-least ' + accepted_age);
}else{
console.log((days - age));
alert('You are not at-least ' + accepted_age);
}
}

This is my modification:
function calculate_age(date) {
var today = new Date();
var today_month = today.getMonth() + 1; //STRANGE NUMBERING //January is 0!
var age = today.getYear() - date.getYear();
if ((today_month > date.getMonth() || ((today_month == date.getMonth()) && (today.getDate() < date.getDate())))) {
age--;
}
return age;
};

I believe that sometimes the readability is more important in this case. Unless we are validating 1000s of fields, this should be accurate and fast enough:
function is18orOlder(dateString) {
const dob = new Date(dateString);
const dobPlus18 = new Date(dob.getFullYear() + 18, dob.getMonth(), dob.getDate());
return dobPlus18 .valueOf() <= Date.now();
}
// Testing:
console.log(is18orOlder('01/01/1910')); // true
console.log(is18orOlder('01/01/2050')); // false
// When I'm posting this on 10/02/2020, so:
console.log(is18orOlder('10/08/2002')); // true
console.log(is18orOlder('10/19/2002')) // false
I like this approach instead of using a constant for how many ms are in a year, and later messing with the leap years, etc. Just letting the built-in Date to do the job.
Update, posting this snippet since one may found it useful. Since I'm enforcing a mask on the input field, to have the format of mm/dd/yyyy and already validating if the date is valid, in my case, this works too to validate 18+ years:
function is18orOlder(dateString) {
const [month, date, year] = value.split('/');
return new Date(+year + 13, +month, +date).valueOf() <= Date.now();
}

Javascript Date string to Age [duplicate]

How can I calculate an age in years, given a birth date of format YYYYMMDD? Is it possible using the Date() function?
I am looking for a better solution than the one I am using now:
var dob = '19800810';
var year = Number(dob.substr(0, 4));
var month = Number(dob.substr(4, 2)) - 1;
var day = Number(dob.substr(6, 2));
var today = new Date();
var age = today.getFullYear() - year;
if (today.getMonth() < month || (today.getMonth() == month && today.getDate() < day)) {
age--;
}
alert(age);

Try this.
function getAge(dateString) {
var today = new Date();
var birthDate = new Date(dateString);
var age = today.getFullYear() - birthDate.getFullYear();
var m = today.getMonth() - birthDate.getMonth();
if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
age--;
}
return age;
}
I believe the only thing that looked crude on your code was the substr part.
Fiddle: http://jsfiddle.net/codeandcloud/n33RJ/

I would go for readability:
function _calculateAge(birthday) { // birthday is a date
var ageDifMs = Date.now() - birthday.getTime();
var ageDate = new Date(ageDifMs); // miliseconds from epoch
return Math.abs(ageDate.getUTCFullYear() - 1970);
}
Disclaimer: This also has precision issues, so this cannot be completely trusted either. It can be off by a few hours, on some years, or during daylight saving (depending on timezone).
Instead I would recommend using a library for this, if precision is very important. Also #Naveens post, is probably the most accurate, as it doesn't rely on the time of day.

Important: This answer doesn't provide an 100% accurate answer, it is off by around 10-20 hours depending on the date.
There are no better solutions ( not in these answers anyway ). - naveen
I of course couldn't resist the urge to take up the challenge and make a faster and shorter birthday calculator than the current accepted solution.
The main point for my solution, is that math is fast, so instead of using branching, and the date model javascript provides to calculate a solution we use the wonderful math
The answer looks like this, and runs ~65% faster than naveen's plus it's much shorter:
function calcAge(dateString) {
var birthday = +new Date(dateString);
return ~~((Date.now() - birthday) / (31557600000));
}
The magic number: 31557600000 is 24 * 3600 * 365.25 * 1000
Which is the length of a year, the length of a year is 365 days and 6 hours which is 0.25 day. In the end i floor the result which gives us the final age.
Here is the benchmarks: http://jsperf.com/birthday-calculation
To support OP's data format you can replace +new Date(dateString);
with +new Date(d.substr(0, 4), d.substr(4, 2)-1, d.substr(6, 2));
If you can come up with a better solution please share! :-)

Clean one-liner solution using ES6:
const getAge = birthDate => Math.floor((new Date() - new Date(birthDate).getTime()) / 3.15576e+10)
// today is 2018-06-13
getAge('1994-06-14') // 23
getAge('1994-06-13') // 24
I am using a year of 365.25 days (0.25 because of leap years) which are 3.15576e+10 milliseconds (365.25 * 24 * 60 * 60 * 1000) respectively.
It has a few hours margin so depending on the use case it may not be the best option.

With momentjs:
/* The difference, in years, between NOW and 2012-05-07 */
moment().diff(moment('20120507', 'YYYYMMDD'), 'years')

Some time ago I made a function with that purpose:
function getAge(birthDate) {
var now = new Date();
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
// days since the birthdate
var days = Math.floor((now.getTime() - birthDate.getTime())/1000/60/60/24);
var age = 0;
// iterate the years
for (var y = birthDate.getFullYear(); y <= now.getFullYear(); y++){
var daysInYear = isLeap(y) ? 366 : 365;
if (days >= daysInYear){
days -= daysInYear;
age++;
// increment the age only if there are available enough days for the year.
}
}
return age;
}
It takes a Date object as input, so you need to parse the 'YYYYMMDD' formatted date string:
var birthDateStr = '19840831',
parts = birthDateStr.match(/(\d{4})(\d{2})(\d{2})/),
dateObj = new Date(parts[1], parts[2]-1, parts[3]); // months 0-based!
getAge(dateObj); // 26

Here's my solution, just pass in a parseable date:
function getAge(birth) {
ageMS = Date.parse(Date()) - Date.parse(birth);
age = new Date();
age.setTime(ageMS);
ageYear = age.getFullYear() - 1970;
return ageYear;
// ageMonth = age.getMonth(); // Accurate calculation of the month part of the age
// ageDay = age.getDate(); // Approximate calculation of the day part of the age
}

Alternate solution, because why not:
function calculateAgeInYears (date) {
var now = new Date();
var current_year = now.getFullYear();
var year_diff = current_year - date.getFullYear();
var birthday_this_year = new Date(current_year, date.getMonth(), date.getDate());
var has_had_birthday_this_year = (now >= birthday_this_year);
return has_had_birthday_this_year
? year_diff
: year_diff - 1;
}

function age()
{
var birthdate = $j('#birthDate').val(); // in "mm/dd/yyyy" format
var senddate = $j('#expireDate').val(); // in "mm/dd/yyyy" format
var x = birthdate.split("/");
var y = senddate.split("/");
var bdays = x[1];
var bmonths = x[0];
var byear = x[2];
//alert(bdays);
var sdays = y[1];
var smonths = y[0];
var syear = y[2];
//alert(sdays);
if(sdays < bdays)
{
sdays = parseInt(sdays) + 30;
smonths = parseInt(smonths) - 1;
//alert(sdays);
var fdays = sdays - bdays;
//alert(fdays);
}
else{
var fdays = sdays - bdays;
}
if(smonths < bmonths)
{
smonths = parseInt(smonths) + 12;
syear = syear - 1;
var fmonths = smonths - bmonths;
}
else
{
var fmonths = smonths - bmonths;
}
var fyear = syear - byear;
document.getElementById('patientAge').value = fyear+' years '+fmonths+' months '+fdays+' days';
}

I think that could be simply like that:
function age(dateString){
let birth = new Date(dateString);
let now = new Date();
let beforeBirth = ((() => {birth.setDate(now.getDate());birth.setMonth(now.getMonth()); return birth.getTime()})() < birth.getTime()) ? 0 : 1;
return now.getFullYear() - birth.getFullYear() - beforeBirth;
}
age('09/20/1981');
//35
Works also with a timestamp
age(403501000000)
//34

That's the most elegant way for me:
const getAge = (birthDateString) => {
const today = new Date();
const birthDate = new Date(birthDateString);
const yearsDifference = today.getFullYear() - birthDate.getFullYear();
if (
today.getMonth() < birthDate.getMonth() ||
(today.getMonth() === birthDate.getMonth() && today.getDate() < birthDate.getDate())
) {
return yearsDifference - 1;
}
return yearsDifference;
};
console.log(getAge('2018-03-12'));

This question is over 10 years old an nobody has addressed the prompt that they already have the birth date in YYYYMMDD format?
If you have a past date and the current date both in YYYYMMDD format, you can very quickly calculate the number of years between them like this:
var pastDate = '20101030';
var currentDate = '20210622';
var years = Math.floor( ( currentDate - pastDate ) * 0.0001 );
// 10 (10.9592)
You can get the current date formatted as YYYYMMDD like this:
var now = new Date();
var currentDate = [
now.getFullYear(),
('0' + (now.getMonth() + 1) ).slice(-2),
('0' + now.getDate() ).slice(-2),
].join('');

To test whether the birthday already passed or not, I define a helper function Date.prototype.getDoY, which effectively returns the day number of the year. The rest is pretty self-explanatory.
Date.prototype.getDoY = function() {
var onejan = new Date(this.getFullYear(), 0, 1);
return Math.floor(((this - onejan) / 86400000) + 1);
};
function getAge(birthDate) {
function isLeap(year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
var now = new Date(),
age = now.getFullYear() - birthDate.getFullYear(),
doyNow = now.getDoY(),
doyBirth = birthDate.getDoY();
// normalize day-of-year in leap years
if (isLeap(now.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyNow--;
if (isLeap(birthDate.getFullYear()) && doyNow > 58 && doyBirth > 59)
doyBirth--;
if (doyNow <= doyBirth)
age--; // birthday not yet passed this year, so -1
return age;
};
var myBirth = new Date(2001, 6, 4);
console.log(getAge(myBirth));

I just had to write this function for myself - the accepted answer is fairly good but IMO could use some cleanup. This takes a unix timestamp for dob because that was my requirement but could be quickly adapted to use a string:
var getAge = function(dob) {
var measureDays = function(dateObj) {
return 31*dateObj.getMonth()+dateObj.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - (measureDays(now) < measureDays(d));
}
Notice I've used a flat value of 31 in my measureDays function. All the calculation cares about is that the "day-of-year" be a monotonically increasing measure of the timestamp.
If using a javascript timestamp or string, obviously you'll want to remove the factor of 1000.

function getAge(dateString) {
var dates = dateString.split("-");
var d = new Date();
var userday = dates[0];
var usermonth = dates[1];
var useryear = dates[2];
var curday = d.getDate();
var curmonth = d.getMonth()+1;
var curyear = d.getFullYear();
var age = curyear - useryear;
if((curmonth < usermonth) || ( (curmonth == usermonth) && curday < userday )){
age--;
}
return age;
}
To get the age when european date has entered:
getAge('16-03-1989')

I've checked the examples showed before and they didn't worked in all cases, and because of this i made a script of my own. I tested this, and it works perfectly.
function getAge(birth) {
var today = new Date();
var curr_date = today.getDate();
var curr_month = today.getMonth() + 1;
var curr_year = today.getFullYear();
var pieces = birth.split('/');
var birth_date = pieces[0];
var birth_month = pieces[1];
var birth_year = pieces[2];
if (curr_month == birth_month && curr_date >= birth_date) return parseInt(curr_year-birth_year);
if (curr_month == birth_month && curr_date < birth_date) return parseInt(curr_year-birth_year-1);
if (curr_month > birth_month) return parseInt(curr_year-birth_year);
if (curr_month < birth_month) return parseInt(curr_year-birth_year-1);
}
var age = getAge('18/01/2011');
alert(age);

Get the age (years, months and days) from the date of birth with javascript
Function calcularEdad (years, months and days)
function calcularEdad(fecha) {
// Si la fecha es correcta, calculamos la edad
if (typeof fecha != "string" && fecha && esNumero(fecha.getTime())) {
fecha = formatDate(fecha, "yyyy-MM-dd");
}
var values = fecha.split("-");
var dia = values[2];
var mes = values[1];
var ano = values[0];
// cogemos los valores actuales
var fecha_hoy = new Date();
var ahora_ano = fecha_hoy.getYear();
var ahora_mes = fecha_hoy.getMonth() + 1;
var ahora_dia = fecha_hoy.getDate();
// realizamos el calculo
var edad = (ahora_ano + 1900) - ano;
if (ahora_mes < mes) {
edad--;
}
if ((mes == ahora_mes) && (ahora_dia < dia)) {
edad--;
}
if (edad > 1900) {
edad -= 1900;
}
// calculamos los meses
var meses = 0;
if (ahora_mes > mes && dia > ahora_dia)
meses = ahora_mes - mes - 1;
else if (ahora_mes > mes)
meses = ahora_mes - mes
if (ahora_mes < mes && dia < ahora_dia)
meses = 12 - (mes - ahora_mes);
else if (ahora_mes < mes)
meses = 12 - (mes - ahora_mes + 1);
if (ahora_mes == mes && dia > ahora_dia)
meses = 11;
// calculamos los dias
var dias = 0;
if (ahora_dia > dia)
dias = ahora_dia - dia;
if (ahora_dia < dia) {
ultimoDiaMes = new Date(ahora_ano, ahora_mes - 1, 0);
dias = ultimoDiaMes.getDate() - (dia - ahora_dia);
}
return edad + " años, " + meses + " meses y " + dias + " días";
}
Function esNumero
function esNumero(strNumber) {
if (strNumber == null) return false;
if (strNumber == undefined) return false;
if (typeof strNumber === "number" && !isNaN(strNumber)) return true;
if (strNumber == "") return false;
if (strNumber === "") return false;
var psInt, psFloat;
psInt = parseInt(strNumber);
psFloat = parseFloat(strNumber);
return !isNaN(strNumber) && !isNaN(psFloat);
}

One more possible solution with moment.js:
var moment = require('moment');
var startDate = new Date();
var endDate = new Date();
endDate.setDate(endDate.getFullYear() + 5); // Add 5 years to second date
console.log(moment.duration(endDate - startDate).years()); // This should returns 5

I am a bit too late but I found this to be the simplest way to calculate a birth date.
Hopefully this will help.
function init() {
writeYears("myage", 0, Age());
}
function Age() {
var birthday = new Date(1997, 02, 01), //Year, month-1 , day.
today = new Date(),
one_year = 1000 * 60 * 60 * 24 * 365;
return Math.floor((today.getTime() - birthday.getTime()) / one_year);
}
function writeYears(id, current, maximum) {
document.getElementById(id).innerHTML = current;
if (current < maximum) {
setTimeout(function() {
writeYears(id, ++current, maximum);
}, Math.sin(current / maximum) * 200);
}
}
init()
<span id="myage"></span>

Works perfect for me, guys.
getAge(birthday) {
const millis = Date.now() - Date.parse(birthday);
return new Date(millis).getFullYear() - 1970;
}

I know this is a very old thread but I wanted to put in this implementation that I wrote for finding the age which I believe is much more accurate.
var getAge = function(year,month,date){
var today = new Date();
var dob = new Date();
dob.setFullYear(year);
dob.setMonth(month-1);
dob.setDate(date);
var timeDiff = today.valueOf() - dob.valueOf();
var milliInDay = 24*60*60*1000;
var noOfDays = timeDiff / milliInDay;
var daysInYear = 365.242;
return ( noOfDays / daysInYear ) ;
}
Ofcourse you could adapt this to fit in other formats of getting the parameters. Hope this helps someone looking for a better solution.

I used this approach using logic instead of math.
It's precise and quick.
The parameters are the year, month and day of the person's birthday.
It returns the person's age as an integer.
function calculateAge(year, month, day) {
var currentDate = new Date();
var currentYear = currentDate.getFullYear();
var currentMonth = currentDate.getUTCMonth() + 1;
var currentDay = currentDate.getUTCDate();
// You need to treat the cases where the year, month or day hasn't arrived yet.
var age = currentYear - year;
if (currentMonth > month) {
return age;
} else {
if (currentDay >= day) {
return age;
} else {
age--;
return age;
}
}
}

Adopting from naveen's and original OP's posts I ended up with a reusable method stub that accepts both strings and / or JS Date objects.
I named it gregorianAge() because this calculation gives exactly how we denote age using Gregorian calendar. i.e. Not counting the end year if month and day is before the month and day of the birth year.
/**
* Calculates human age in years given a birth day. Optionally ageAtDate
* can be provided to calculate age at a specific date
*
* #param string|Date Object birthDate
* #param string|Date Object ageAtDate optional
* #returns integer Age between birthday and a given date or today
*/
function gregorianAge(birthDate, ageAtDate) {
// convert birthDate to date object if already not
if (Object.prototype.toString.call(birthDate) !== '[object Date]')
birthDate = new Date(birthDate);
// use today's date if ageAtDate is not provided
if (typeof ageAtDate == "undefined")
ageAtDate = new Date();
// convert ageAtDate to date object if already not
else if (Object.prototype.toString.call(ageAtDate) !== '[object Date]')
ageAtDate = new Date(ageAtDate);
// if conversion to date object fails return null
if (ageAtDate == null || birthDate == null)
return null;
var _m = ageAtDate.getMonth() - birthDate.getMonth();
// answer: ageAt year minus birth year less one (1) if month and day of
// ageAt year is before month and day of birth year
return (ageAtDate.getFullYear()) - birthDate.getFullYear()
- ((_m < 0 || (_m === 0 && ageAtDate.getDate() < birthDate.getDate())) ? 1 : 0)
}
// Below is for the attached snippet
function showAge() {
$('#age').text(gregorianAge($('#dob').val()))
}
$(function() {
$(".datepicker").datepicker();
showAge();
});
<link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="//code.jquery.com/jquery-1.10.2.js"></script>
<script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
DOB:
<input name="dob" value="12/31/1970" id="dob" class="datepicker" onChange="showAge()" /> AGE: <span id="age"><span>

Two more options:
// Int Age to Date as string YYY-mm-dd
function age_to_date(age)
{
try {
var d = new Date();
var new_d = '';
d.setFullYear(d.getFullYear() - Math.abs(age));
new_d = d.getFullYear() + '-' + d.getMonth() + '-' + d.getDate();
return new_d;
} catch(err) {
console.log(err.message);
}
}
// Date string (YYY-mm-dd) to Int age (years old)
function date_to_age(date)
{
try {
var today = new Date();
var d = new Date(date);
var year = today.getFullYear() - d.getFullYear();
var month = today.getMonth() - d.getMonth();
var day = today.getDate() - d.getDate();
var carry = 0;
if (year < 0)
return 0;
if (month <= 0 && day <= 0)
carry -= 1;
var age = parseInt(year);
age += carry;
return Math.abs(age);
} catch(err) {
console.log(err.message);
}
}

I've did some updated to one previous answer.
var calculateAge = function(dob) {
var days = function(date) {
return 31*date.getMonth() + date.getDate();
},
d = new Date(dob*1000),
now = new Date();
return now.getFullYear() - d.getFullYear() - ( measureDays(now) < measureDays(d));
}
I hope that helps :D

here is a simple way of calculating age:
//dob date dd/mm/yy
var d = 01/01/1990
//today
//date today string format
var today = new Date(); // i.e wed 04 may 2016 15:12:09 GMT
//todays year
var todayYear = today.getFullYear();
// today month
var todayMonth = today.getMonth();
//today date
var todayDate = today.getDate();
//dob
//dob parsed as date format
var dob = new Date(d);
// dob year
var dobYear = dob.getFullYear();
// dob month
var dobMonth = dob.getMonth();
//dob date
var dobDate = dob.getDate();
var yearsDiff = todayYear - dobYear ;
var age;
if ( todayMonth < dobMonth )
{
age = yearsDiff - 1;
}
else if ( todayMonth > dobMonth )
{
age = yearsDiff ;
}
else //if today month = dob month
{ if ( todayDate < dobDate )
{
age = yearsDiff - 1;
}
else
{
age = yearsDiff;
}
}

var now = DateTime.Now;
var age = DateTime.Now.Year - dob.Year;
if (now.Month < dob.Month || now.Month == dob.Month && now.Day < dob.Day) age--;

You may use this for age restriction in your form -
function dobvalidator(birthDateString){
strs = birthDateString.split("-");
var dd = strs[0];
var mm = strs[1];
var yy = strs[2];
var d = new Date();
var ds = d.getDate();
var ms = d.getMonth();
var ys = d.getFullYear();
var accepted_age = 18;
var days = ((accepted_age * 12) * 30) + (ms * 30) + ds;
var age = (((ys - yy) * 12) * 30) + ((12 - mm) * 30) + parseInt(30 - dd);
if((days - age) <= '0'){
console.log((days - age));
alert('You are at-least ' + accepted_age);
}else{
console.log((days - age));
alert('You are not at-least ' + accepted_age);
}
}

This is my modification:
function calculate_age(date) {
var today = new Date();
var today_month = today.getMonth() + 1; //STRANGE NUMBERING //January is 0!
var age = today.getYear() - date.getYear();
if ((today_month > date.getMonth() || ((today_month == date.getMonth()) && (today.getDate() < date.getDate())))) {
age--;
}
return age;
};

I believe that sometimes the readability is more important in this case. Unless we are validating 1000s of fields, this should be accurate and fast enough:
function is18orOlder(dateString) {
const dob = new Date(dateString);
const dobPlus18 = new Date(dob.getFullYear() + 18, dob.getMonth(), dob.getDate());
return dobPlus18 .valueOf() <= Date.now();
}
// Testing:
console.log(is18orOlder('01/01/1910')); // true
console.log(is18orOlder('01/01/2050')); // false
// When I'm posting this on 10/02/2020, so:
console.log(is18orOlder('10/08/2002')); // true
console.log(is18orOlder('10/19/2002')) // false
I like this approach instead of using a constant for how many ms are in a year, and later messing with the leap years, etc. Just letting the built-in Date to do the job.
Update, posting this snippet since one may found it useful. Since I'm enforcing a mask on the input field, to have the format of mm/dd/yyyy and already validating if the date is valid, in my case, this works too to validate 18+ years:
function is18orOlder(dateString) {
const [month, date, year] = value.split('/');
return new Date(+year + 13, +month, +date).valueOf() <= Date.now();
}

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