JavaScript function to add X months to a date

JavaScript function to add X months to a date

I’m looking for the easiest, cleanest way to add X months to a JavaScript date.
I’d rather not handle the rolling over of the year or have to write my own function.
Is there something built in that can do this?

Solutions/Answers:

Solution 1:

I think this should do it:

var x = 12; //or whatever offset
var CurrentDate = new Date();
console.log("Current date:", CurrentDate);
CurrentDate.setMonth(CurrentDate.getMonth() + x);
console.log("Date after " + x + " months:", CurrentDate);

I believe it should automatically handle incrementing to the appropriate year and mod-ing to the appropriate month.

Solution 2:

I’m using moment.js library for date-time manipulations.
Sample code to add one month:

var startDate = new Date(...);
var endDateMoment = moment(startDate); // moment(...) can also be used to parse dates in string format
endDateMoment.add(1, 'months');

Solution 3:

This function handles edge cases and is fast:

function addMonthsUTC (date, count) {
  if (date && count) {
    var m, d = (date = new Date(+date)).getUTCDate()

    date.setUTCMonth(date.getUTCMonth() + count, 1)
    m = date.getUTCMonth()
    date.setUTCDate(d)
    if (date.getUTCMonth() !== m) date.setUTCDate(0)
  }
  return date
}

test:

> d = new Date('2016-01-31T00:00:00Z');
Sat Jan 30 2016 18:00:00 GMT-0600 (CST)
> d = addMonthsUTC(d, 1);
Sun Feb 28 2016 18:00:00 GMT-0600 (CST)
> d = addMonthsUTC(d, 1);
Mon Mar 28 2016 18:00:00 GMT-0600 (CST)
> d.toISOString()
"2016-03-29T00:00:00.000Z"

Update for non-UTC dates: (by A.Hatchkins)

function addMonths (date, count) {
  if (date && count) {
    var m, d = (date = new Date(+date)).getDate()

    date.setMonth(date.getMonth() + count, 1)
    m = date.getMonth()
    date.setDate(d)
    if (date.getMonth() !== m) date.setDate(0)
  }
  return date
}

test:

> d = new Date(2016,0,31);
Sun Jan 31 2016 00:00:00 GMT-0600 (CST)
> d = addMonths(d, 1);
Mon Feb 29 2016 00:00:00 GMT-0600 (CST)
> d = addMonths(d, 1);
Tue Mar 29 2016 00:00:00 GMT-0600 (CST)
> d.toISOString()
"2016-03-29T06:00:00.000Z"

Solution 4:

Considering none of these answers will account for the current year when the month changes, you can find one I made below which should handle it:

Related:  Why does asm.js deteriorate performance?

The method:

Date.prototype.addMonths = function (m) {
    var d = new Date(this);
    var years = Math.floor(m / 12);
    var months = m - (years * 12);
    if (years) d.setFullYear(d.getFullYear() + years);
    if (months) d.setMonth(d.getMonth() + months);
    return d;
}

Usage:

return new Date().addMonths(2);

Solution 5:

Taken from @bmpsini and @Jazaret responses, but not extending prototypes: using plain functions (Why is extending native objects a bad practice?):

function isLeapYear(year) { 
    return (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)); 
}

function getDaysInMonth(year, month) {
    return [31, (isLeapYear(year) ? 29 : 28), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month];
}

function addMonths(date, value) {
    var d = new Date(date),
        n = date.getDate();
    d.setDate(1);
    d.setMonth(d.getMonth() + value);
    d.setDate(Math.min(n, getDaysInMonth(d.getFullYear(), d.getMonth())));
    return d;
}

Use it:

var nextMonth = addMonths(new Date(), 1);

Solution 6:

Simple solution: 2678400000 is 31 day in milliseconds

var oneMonthFromNow = new Date((+new Date) + 2678400000);

Update:

Use this data to build our own function:

  • 2678400000 – 31 day
  • 2592000000 – 30 days
  • 2505600000 – 29 days
  • 2419200000 – 28 days