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Calculate time remaining between now and a precise hour of next day

What's the most concise, performant way to get in Javascript the minutes remaining between now, and the upcoming day at 01:00 (am)?
Then, once the current time is after 01:00, I start calculating the difference to the next.

in javascript, a specified date can be provided like this
var date1 = new Date('June 6, 2019 03:24:00');
or it can be specified like this
var date2 = new Date('2019-6-6T03:24:00');
javascript can natively subtract 2 dates
console.log(date1 - date2);
//expected 0;
using this method will output the difference in the dates in milliseconds,
to get minutes you'll want to divide the value by 60000;
so
var futureTime = new Date('2019-06-06T07:24:00');
//there must be a 0 infront of 1 digit numbers or it is an invalid date
var now = new Date();
var difference = (futureTime - now) / 60000;
//get minutes by dividing by 60000
//doing Date() with no arguments returns the current date
read about the javascript Date object here for more information
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date

let now = new Date();
let next1am = new Date();
next1am.setHours(1, 0, 0, 0); // same as now, but at 01:00:00.000
if (next1am < now) next1am.setDate(next1am.getDate() + 1); // bump date if past
let millisecondDiff = next1am - now;
let minuteDiff = Math.floor(millisecondDiff / 1000 / 60);

you can you moment.js here
var current = new Date()
var end = new Date(start.getTime() + 3600*60)// end time to calculate diff
var minDiff = end - start; // in millisec

You can calculate by pure JavaScript:
let today = new Date();
let [y,M,d,h,m,s] = '2019-06-04 05:00:11'.split(/[- :]/);
let yourDate = new Date(y,parseInt(M)-1,d,h,parseInt(m)+30,s);
let diffMs = (yourDate - today);
let diffDays = Math.floor(diffMs / 86400000); // days
let diffHrs = Math.floor((diffMs % 86400000) / 3600000); // hours
let diffMins = (diffDays * 24 * 60)
+ (diffHrs *60)
+ Math.round(((diffMs % 86400000) % 3600000) / 60000); // The overall result
// in minutes
In, addition avoid using the built–in parser for any non–standard format, e.g. in Safari new Date("2019-04-22 05:00:11") returns an invalid date. You really shouldn't even use if for standardized formats as you will still get unexpected results for some formats. Why does Date.parse give incorrect results?

compare date in javascript format 06/01/2014 13:24

I am trying to compare two dates in javascript, which are in two input type="text", and that have the format "06/11/2013 13:24".
Any idea of how to compare them?
Thanks!

You need to parse string to Date - object:
var firstDate = new Date("06/11/2013 13:24");
var secondDate = new Date(youSecondDateString);

Age from Date of Birth using JQuery
Possibly a duplicate question to above but the answers is
var startDt=document.getElementById("startDateId").value;
var endDt=document.getElementById("endDateId").value;
if( (new Date(startDt).getTime() > new Date(endDt).getTime()))
{
//perform desired operation here
}

The Date object will do what you want - construct one for each date, then just compare them using the usual operators.
For example, subtracting date1 from date2 will give you the number of milliseconds between two dates.
You can get the number of seconds by dividing the milliseconds by 1000, and rounding the number:
var seconds = Math.round((date2-date1)/1000);
You could then divide by 60 to get the minutes, again by 60 to get the hours, then by 24 to get the days (and so on).
Here's how you might get a figure in the format dd:hh:mm
window.minutesPerDay = 60 * 24;
function pad(number) {
var result = "" + number;
if (result.length < 2) {
result = "0" + result;
}
return result;
}
function millisToDaysHoursMinutes(millis) {
var seconds = millis / 1000;
var totalMinutes = seconds / 60;
var days = totalMinutes / minutesPerDay;
totalMinutes -= minutesPerDay * days;
var hours = totalMinutes / 60;
totalMinutes -= hours * 60;
return days + ":" + pad(hours) + ":" + pad(totalMinutes);
}
var date1 = new Date("06/11/2013 13:24"),
date2 = new Date("07/11/2013 13:24"),
milliseconds = date2 - date1;
alert(millisToDaysHoursMinutes(milliseconds));
Fiddle
I took the millisToDaysHoursMinutes function from here.

How to calculate number of days between two dates

I have two input dates taking from Date Picker control. I have selected start date 2/2/2012 and end date 2/7/2012. I have written following code for that.
I should get result as 6 but I am getting 5.
function SetDays(invoker) {
var start = $find('<%=StartWebDatePicker.ClientID%>').get_value();
var end = $find('<%=EndWebDatePicker.ClientID%>').get_value();
var oneDay=1000 * 60 * 60 * 24;
var difference_ms = Math.abs(end.getTime() - start.getTime())
var diffValue = Math.round(difference_ms / oneDay);
}
Can anyone tell me how I can get exact difference?

http://momentjs.com/ or https://date-fns.org/
From Moment docs:
var a = moment([2007, 0, 29]);
var b = moment([2007, 0, 28]);
a.diff(b, 'days') // =1
or to include the start:
a.diff(b, 'days')+1 // =2
Beats messing with timestamps and time zones manually.
Depending on your specific use case, you can either
Use a/b.startOf('day') and/or a/b.endOf('day') to force the diff to be inclusive or exclusive at the "ends" (as suggested by #kotpal in the comments).
Set third argument true to get a floating point diff which you can then Math.floor, Math.ceil or Math.round as needed.
Option 2 can also be accomplished by getting 'seconds' instead of 'days' and then dividing by 24*60*60.

If you are using moment.js you can do it easily.
var start = moment("2018-03-10", "YYYY-MM-DD");
var end = moment("2018-03-15", "YYYY-MM-DD");
//Difference in number of days
moment.duration(start.diff(end)).asDays();
//Difference in number of weeks
moment.duration(start.diff(end)).asWeeks();
If you want to find difference between a given date and current date in number of days (ignoring time), make sure to remove time from moment object of current date as below
moment().startOf('day')
To find difference between a given date and current date in number of days
var given = moment("2018-03-10", "YYYY-MM-DD");
var current = moment().startOf('day');
//Difference in number of days
moment.duration(given.diff(current)).asDays();

Try this Using moment.js (Its quite easy to compute date operations in javascript)
firstDate.diff(secondDate, 'days', false);// true|false for fraction value
Result will give you number of days in integer.

Try:
//Difference in days
var diff = Math.floor(( start - end ) / 86400000);
alert(diff);

This works for me:
const from = '2019-01-01';
const to = '2019-01-08';
Math.abs(
moment(from, 'YYYY-MM-DD')
.startOf('day')
.diff(moment(to, 'YYYY-MM-DD').startOf('day'), 'days')
) + 1
);

I made a quick re-usable function in ES6 using Moment.js.
const getDaysDiff = (start_date, end_date, date_format = 'YYYY-MM-DD') => {
const getDateAsArray = (date) => {
return moment(date.split(/\D+/), date_format);
}
return getDateAsArray(end_date).diff(getDateAsArray(start_date), 'days') + 1;
}
console.log(getDaysDiff('2019-10-01', '2019-10-30'));
console.log(getDaysDiff('2019/10/01', '2019/10/30'));
console.log(getDaysDiff('2019.10-01', '2019.10 30'));
console.log(getDaysDiff('2019 10 01', '2019 10 30'));
console.log(getDaysDiff('+++++2019!!/###10/$$01', '2019-10-30'));
console.log(getDaysDiff('2019-10-01-2019', '2019-10-30'));
console.log(getDaysDiff('10-01-2019', '10-30-2019', 'MM-DD-YYYY'));
console.log(getDaysDiff('10-01-2019', '10-30-2019'));
console.log(getDaysDiff('10-01-2019', '2019-10-30', 'MM-DD-YYYY'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.js"></script>

Also you can use this code: moment("yourDateHere", "YYYY-MM-DD").fromNow(). This will calculate the difference between today and your provided date.

// today
const date = new Date();
// tomorrow
const nextDay = new Date(new Date().getTime() + 24 * 60 * 60 * 1000);
// Difference in time
const Difference_In_Time = nextDay.getTime() - date.getTime();
// Difference in Days
const Difference_In_Days = Difference_In_Time / (1000 * 3600 * 24);

Finding date by subtracting X number of days from a particular date in Javascript

I want to find date by subtracting X number of days from a particular date in JavaScript. My JavaScript function accepts 2 parameters. One is the date value and the other is the number of days that needs to be subtracted.
For example, I pass my argument date as 27 July 2009 and i pass my other argument as 3. So i want to calculate the date 3 days before 27 July 2009. So the resultant date that we should get is 24 July 2009. How is this possible in JavaScript. Thanks for any help.

Simply:
yourDate.setDate(yourDate.getDate() - daysToSubtract);

function date_by_subtracting_days(date, days) {
return new Date(
date.getFullYear(),
date.getMonth(),
date.getDate() - days,
date.getHours(),
date.getMinutes(),
date.getSeconds(),
date.getMilliseconds()
);
}

Never go for this solution
yourDate.setDate(yourDate.getDate() - daysToSubtract);
it wont work in case your date is 1st of any month and you want to delete some days say 1.
Instead go for below solution which will work always
var newDate = new Date( yourDate.getTime() - (days * 24 * 60 * 60 * 1000) );

Here i am posting one more answer and that will return date in specific format.
First you can get current date 10/08/2013 as below
function Cureent_Date() {
var today_GMT = new Date();
var dd = today_GMT.getDate();
var mm = today_GMT.getMonth() + 1; //January is 0!
var yyyy = today_GMT.getFullYear();
if (dd < 10) {
dd = '0' + dd
}
if (mm < 10) {
mm = '0' + mm
}
current_date = mm + '/' + dd + '/' + yyyy;
alert("current_date"+current_date);
Back_date();
}
Now Get back date base on X days
function Back_date()
{
var back_GTM = new Date(); back_GTM.setDate(back_GTM.getDate() - 2); // 2 is your X
var b_dd = back_GTM.getDate();
var b_mm = back_GTM.getMonth()+1;
var b_yyyy = back_GTM.getFullYear();
if (b_dd < 10) {
b_dd = '0' + b_dd
}
if (b_mm < 10) {
b_mm = '0' +b_mm
}
var back_date= b_mm + '/' + b_dd + '/' + b_yyyy;
alert("back_date"+back_date);
}
So, Today is 10/08/2013 so it will return 10/06/2013.
Check Live Demo here
Hope this answer will help you.

Here's an example, however this does no kind of checking (for example if you use it on 2009/7/1 it'll use a negative day or throw an error.
function subDate(o, days) {
// keep in mind, months in javascript are 0-11
return new Date(o.getFullYear(), o.getMonth(), o.getDate() - days);;
}

This is what I would do. Note you can simplify the expression, I've just written it out to make it clear you are multiplying the number of days by the number of milliseconds in a day.
var newDate = new Date( yourDate.getTime() - (days * 24 * 60 * 60 * 1000) );

Just another option, which I wrote:
DP_DateExtensions Library
It's probably overkill if ALL you want to do is one calculation, but if you're going to do more date manipulation you might find it useful.
Supports date/time formatting, date math (add/subtract date parts), date compare, date parsing, etc.

this is in reference to above answer
check this fiddle
https://jsfiddle.net/uniyalguru/azh65aa0/
function Cureent_Date() {
var today_GMT = new Date();
var dd = today_GMT.getDate();
var mm = today_GMT.getMonth() + 1; //January is 0!
var yyyy = today_GMT.getFullYear();
if (dd < 10) {
dd = '0' + dd
}
if (mm < 10) {
mm = '0' + mm
}
current_date = mm + '/' + dd + '/' + yyyy;

I have created a function for date manipulation. you can add or subtract any number of days, hours, minutes.
function dateManipulation(date, days, hrs, mins, operator) {
date = new Date(date);
if (operator == "-") {
var durationInMs = (((24 * days) * 60) + (hrs * 60) + mins) * 60000;
var newDate = new Date(date.getTime() - durationInMs);
} else {
var durationInMs = (((24 * days) * 60) + (hrs * 60) + mins) * 60000;
var newDate = new Date(date.getTime() + durationInMs);
}
return newDate;
}
Now, call this function by passing parameters. For example, here is a function call for getting date before 3 days from today.
var today = new Date();
var newDate = dateManipulation(today, 3, 0, 0, "-");

How to subtract days from a plain Date?

Want to improve this post? Provide detailed answers to this question, including citations and an explanation of why your answer is correct. Answers without enough detail may be edited or deleted.
Is there an easy way of taking a olain JavaScript Date (e.g. today) and going back X days?
So, for example, if I want to calculate the date 5 days before today.

Try something like this:
var d = new Date();
d.setDate(d.getDate()-5);
Note that this modifies the date object and returns the time value of the updated date.
var d = new Date();
document.write('Today is: ' + d.toLocaleString());
d.setDate(d.getDate() - 5);
document.write('<br>5 days ago was: ' + d.toLocaleString());

var dateOffset = (24*60*60*1000) * 5; //5 days
var myDate = new Date();
myDate.setTime(myDate.getTime() - dateOffset);
If you're performing lots of headachy date manipulation throughout your web application, DateJS will make your life much easier:
http://simonwillison.net/2007/Dec/3/datejs/

It goes something like this:
var d = new Date(); // today!
var x = 5; // go back 5 days!
d.setDate(d.getDate() - x);

I noticed that the getDays+ X doesn't work over day/month boundaries. Using getTime works as long as your date is not before 1970.
var todayDate = new Date(), weekDate = new Date();
weekDate.setTime(todayDate.getTime()-(7*24*3600000));

If you want it all on one line instead.
5 days from today
//past
var fiveDaysAgo = new Date(new Date().setDate(new Date().getDate() - 5));
//future
var fiveDaysInTheFuture = new Date(new Date().setDate(new Date().getDate() + 5));
5 days from a specific date
var pastDate = new Date('2019-12-12T00:00:00');
//past
var fiveDaysAgo = new Date(new Date().setDate(pastDate.getDate() - 5));
//future
var fiveDaysInTheFuture = new Date(new Date().setDate(pastDate.getDate() + 5));
I wrote a function you can use.
function AddOrSubractDays(startingDate, number, add) {
if (add) {
return new Date(new Date().setDate(startingDate.getDate() + number));
} else {
return new Date(new Date().setDate(startingDate.getDate() - number));
}
}
console.log('Today : ' + new Date());
console.log('Future : ' + AddOrSubractDays(new Date(), 5, true));
console.log('Past : ' + AddOrSubractDays(new Date(), 5, false));

I find a problem with the getDate()/setDate() method is that it too easily turns everything into milliseconds, and the syntax is sometimes hard for me to follow.
Instead I like to work off the fact that 1 day = 86,400,000 milliseconds.
So, for your particular question:
today = new Date()
days = 86400000 //number of milliseconds in a day
fiveDaysAgo = new Date(today - (5*days))
Works like a charm.
I use this method all the time for doing rolling 30/60/365 day calculations.
You can easily extrapolate this to create units of time for months, years, etc.

get moment.js. All the cool kids use it. It has more formatting options, etc. Where
var n = 5;
var dateMnsFive = moment(<your date>).subtract(n , 'day');
Optional! Convert to JS Date obj for Angular binding.
var date = new Date(dateMnsFive.toISOString());
Optional! Format
var date = dateMnsFive.format("YYYY-MM-DD");

A few of the existing solutions were close, but not quite exactly what I wanted. This function works with both positive or negative values and handles boundary cases.
function addDays(date, days) {
return new Date(
date.getFullYear(),
date.getMonth(),
date.getDate() + days,
date.getHours(),
date.getMinutes(),
date.getSeconds(),
date.getMilliseconds()
);
}

Without using the second variable, you can replace 7 for with your back x days:
let d=new Date(new Date().getTime() - (7 * 24 * 60 * 60 * 1000))

I made this prototype for Date so that I could pass negative values to subtract days and positive values to add days.
if(!Date.prototype.adjustDate){
Date.prototype.adjustDate = function(days){
var date;
days = days || 0;
if(days === 0){
date = new Date( this.getTime() );
} else if(days > 0) {
date = new Date( this.getTime() );
date.setDate(date.getDate() + days);
} else {
date = new Date(
this.getFullYear(),
this.getMonth(),
this.getDate() - Math.abs(days),
this.getHours(),
this.getMinutes(),
this.getSeconds(),
this.getMilliseconds()
);
}
this.setTime(date.getTime());
return this;
};
}
So, to use it i can simply write:
var date_subtract = new Date().adjustDate(-4),
date_add = new Date().adjustDate(4);

I like doing the maths in milliseconds. So use Date.now()
var newDate = Date.now() + -5*24*3600*1000; // date 5 days ago in milliseconds
and if you like it formatted
new Date(newDate).toString(); // or .toUTCString or .toISOString ...
NOTE: Date.now() doesn't work in older browsers (eg IE8 I think). Polyfill here.
UPDATE June 2015
#socketpair pointed out my sloppiness. As s/he says "Some day in year have 23 hours, and some 25 due to timezone rules".
To expand on that, the answer above will have daylightsaving inaccuracies in the case where you want to calculate the LOCAL day 5 days ago in a timezone with daylightsaving changes and you
assume (wrongly) that Date.now() gives you the current LOCAL now time, or
use .toString() which returns the local date and therefore is incompatible with the Date.now() base date in UTC.
However, it works if you're doing your math all in UTC, eg
A. You want the UTC date 5 days ago from NOW (UTC)
var newDate = Date.now() + -5*24*3600*1000; // date 5 days ago in milliseconds UTC
new Date(newDate).toUTCString(); // or .toISOString(), BUT NOT toString
B. You start with a UTC base date other than "now", using Date.UTC()
newDate = new Date(Date.UTC(2015, 3, 1)).getTime() + -5*24*3600000;
new Date(newDate).toUTCString(); // or .toISOString BUT NOT toString

split your date into parts, then return a new Date with the adjusted values
function DateAdd(date, type, amount){
var y = date.getFullYear(),
m = date.getMonth(),
d = date.getDate();
if(type === 'y'){
y += amount;
};
if(type === 'm'){
m += amount;
};
if(type === 'd'){
d += amount;
};
return new Date(y, m, d);
}
Remember that the months are zero based, but the days are not. ie new Date(2009, 1, 1) == 01 February 2009, new Date(2009, 1, 0) == 31 January 2009;

Some people suggested using moment.js to make your life easier when handling dates in js. Time has passed since those answers and it is noteworthy, that the authors of moment.js now discourage its use. Mainly due to its size and lack of tree-shaking-support.
If you want to go the library route, use an alternative like Luxon. It is significantly smaller (because of its clever use of the Intl object and support for tree-shaking) and just as versatile as moment.js.
To go back 5 days from today in Luxon, you would do:
import { DateTime } from 'luxon'
DateTime.now().minus({ days: 5 });

function addDays (date, daysToAdd) {
var _24HoursInMilliseconds = 86400000;
return new Date(date.getTime() + daysToAdd * _24HoursInMilliseconds);
};
var now = new Date();
var yesterday = addDays(now, - 1);
var tomorrow = addDays(now, 1);

See the following code, subtract the days from the current date. Also, set the month according to substracted date.
var today = new Date();
var substract_no_of_days = 25;
today.setTime(today.getTime() - substract_no_of_days* 24 * 60 * 60 * 1000);
var substracted_date = (today.getMonth()+1) + "/" +today.getDate() + "/" + today.getFullYear();
alert(substracted_date);

I have created a function for date manipulation. you can add or subtract any number of days, hours, minutes.
function dateManipulation(date, days, hrs, mins, operator) {
date = new Date(date);
if (operator == "-") {
var durationInMs = (((24 * days) * 60) + (hrs * 60) + mins) * 60000;
var newDate = new Date(date.getTime() - durationInMs);
} else {
var durationInMs = (((24 * days) * 60) + (hrs * 60) + mins) * 60000;
var newDate = new Date(date.getTime() + durationInMs);
}
return newDate;
}
Now, call this function by passing parameters. For example, here is a function call for getting date before 3 days from today.
var today = new Date();
var newDate = dateManipulation(today, 3, 0, 0, "-");

Use MomentJS.
function getXDaysBeforeDate(referenceDate, x) {
return moment(referenceDate).subtract(x , 'day').format('MMMM Do YYYY, h:mm:ss a');
}
var yourDate = new Date(); // let's say today
var valueOfX = 7; // let's say 7 days before
console.log(getXDaysBeforeDate(yourDate, valueOfX));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>

The top answers led to a bug in my code where on the first of the month it would set a future date in the current month. Here is what I did,
curDate = new Date(); // Took current date as an example
prvDate = new Date(0); // Date set to epoch 0
prvDate.setUTCMilliseconds((curDate - (5 * 24 * 60 * 60 * 1000))); //Set epoch time

I like the following because it is one line. Not perfect with DST changes but usually good enough for my needs.
var fiveDaysAgo = new Date(new Date() - (1000*60*60*24*5));

Using Modern JavaScript function syntax
const getDaysPastDate = (daysBefore, date = new Date) => new Date(date - (1000 * 60 * 60 * 24 * daysBefore));
console.log(getDaysPastDate(1)); // yesterday

A easy way to manage dates is use Moment.js
You can use add. Example
var startdate = "20.03.2014";
var new_date = moment(startdate, "DD.MM.YYYY");
new_date.add(5, 'days'); //Add 5 days to start date
alert(new_date);
Docs http://momentjs.com/docs/#/manipulating/add/

for me all the combinations worked fine with below code snipplet ,
the snippet is for Angular-2 implementation ,
if you need to add days , pass positive numberofDays , if you need to substract pass negative numberofDays
function addSubstractDays(date: Date, numberofDays: number): Date {
let d = new Date(date);
return new Date(
d.getFullYear(),
d.getMonth(),
(d.getDate() + numberofDays)
);
}

I get good mileage out of date.js:
http://www.datejs.com/
d = new Date();
d.add(-10).days(); // subtract 10 days
Nice!
Website includes this beauty:
Datejs doesn’t just parse strings, it slices them cleanly in two

If you want to both subtract a number of days and format your date in a human readable format, you should consider creating a custom DateHelper object that looks something like this :
var DateHelper = {
addDays : function(aDate, numberOfDays) {
aDate.setDate(aDate.getDate() + numberOfDays); // Add numberOfDays
return aDate; // Return the date
},
format : function format(date) {
return [
("0" + date.getDate()).slice(-2), // Get day and pad it with zeroes
("0" + (date.getMonth()+1)).slice(-2), // Get month and pad it with zeroes
date.getFullYear() // Get full year
].join('/'); // Glue the pieces together
}
}
// With this helper, you can now just use one line of readable code to :
// ---------------------------------------------------------------------
// 1. Get the current date
// 2. Subtract 5 days
// 3. Format it
// 4. Output it
// ---------------------------------------------------------------------
document.body.innerHTML = DateHelper.format(DateHelper.addDays(new Date(), -5));
(see also this Fiddle)

To calculate relative time stamps with a more precise difference than whole days, you can use Date.getTime() and Date.setTime() to work with integers representing the number of milliseconds since a certain epoch—namely, January 1, 1970. For example, if you want to know when it’s 17 hours after right now:
const msSinceEpoch = (new Date()).getTime();
const fortyEightHoursLater = new Date(msSinceEpoch + 48 * 60 * 60 * 1000).toLocaleString();
const fortyEightHoursEarlier = new Date(msSinceEpoch - 48 * 60 * 60 * 1000).toLocaleString();
const fiveDaysAgo = new Date(msSinceEpoch - 120 * 60 * 60 * 1000).toLocaleString();
console.log({msSinceEpoch, fortyEightHoursLater, fortyEightHoursEarlier, fiveDaysAgo})
reference

function daysSinceGivenDate (date) {
const dateInSeconds = Math.floor((new Date().valueOf() - date.valueOf()) / 1000);
const oneDayInSeconds = 86400;
return Math.floor(dateInSeconds / oneDayInSeconds); // casted to int
};
console.log(daysSinceGivenDate(new Date())); // 0
console.log(daysSinceGivenDate(new Date("January 1, 2022 03:24:00"))); // relative...

First arg is the date to start with and second is how mush day you want to increase or reduce to the date
example (1)- pass -1 to reduce date by one day
example (2)- pass 1 to increase date by one day
const EditDay = (date: Date, num: number): Date => {
return new Date(date.getTime() + num * 24 * 60 * 60 * 1000)
}

When setting the date, the date converts to milliseconds, so you need to convert it back to a date:
This method also take into consideration, new year change etc.
function addDays( date, days ) {
var dateInMs = date.setDate(date.getDate() - days);
return new Date(dateInMs);
}
var date_from = new Date();
var date_to = addDays( new Date(), parseInt(days) );

You can using Javascript.
var CurrDate = new Date(); // Current Date
var numberOfDays = 5;
var days = CurrDate.setDate(CurrDate.getDate() + numberOfDays);
alert(days); // It will print 5 days before today
For PHP,
$date = date('Y-m-d', strtotime("-5 days")); // it shows 5 days before today.
echo $date;
Hope it will help you.

I converted into millisecond and deducted days else month and year won't change and logical
var numberOfDays = 10;//number of days need to deducted or added
var date = "01-01-2018"// date need to change
var dt = new Date(parseInt(date.substring(6), 10), // Year
parseInt(date.substring(3,5), 10) - 1, // Month (0-11)
parseInt(date.substring(0,2), 10));
var new_dt = dt.setMilliseconds(dt.getMilliseconds() - numberOfDays*24*60*60*1000);
new_dt = new Date(new_dt);
var changed_date = new_dt.getDate()+"-"+(new_dt.getMonth()+1)+"-"+new_dt.getFullYear();
Hope helps