JavaScript function to add X months to a date

Question

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

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As most of the answers highlighted  we could use setMonth   method together with getMonth   method to add specific number of months to a given date   Example   as mentioned by  ChadD in his answer        var x   12    or whatever offset  var CurrentDate   new Date    CurrentDate setMonth CurrentDate getMonth     x      But we should carefully use this solution as we will get trouble with edge cases    To handle edge cases  answer which is given in following link is helpful   https   stackoverflow com a 13633692 3668866

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Just to add on to the accepted answer and the comments   var x   12    or whatever offset var CurrentDate   new Date       For the very rare cases like the end of a month   eg  May 30th - 3 months will give you March instead of February var date   CurrentDate getDate    CurrentDate setDate 1   CurrentDate setMonth CurrentDate getMonth   X   CurrentDate setDate date

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The following is an example of how to calculate a future date based on date input  membershipssignup date    added months  membershipsmonths  via form fields   The membershipsmonths field has a default value of 0  Trigger link  can be an onchange event attached to membership term field     lt a href     onclick  calculateMshipExp     return false   gt Calculate Expiry Date lt  a gt   function calculateMshipExp      var calcval   null   var start date   document getElementById  membershipssignup date   value  var term   document getElementById  membershipsmonths   value      Is text value  var set start   start date split          var day   set start 0     var month    set start 1  - 1       January is 0 so August  8th month  is 7 var year   set start 2   var datetime   new Date year  month  day   var newmonth    month   parseInt term        Must convert term to integer var newdate   datetime setMonth newmonth    newdate   new Date newdate     alert newdate    day   newdate getDate    month   newdate getMonth     1  year   newdate getFullYear        This is British date format  See below for US  calcval      day  lt   9     0    day   day            month  lt   9     0    month   month          year       mm dd yyyy calcval      month  lt   9     0    month   month            day  lt   9     0    day   day          year       Displays the new date in a  lt span id  memexp  gt  Date  lt  span gt     Note  Must contain a value to replace eg   Date  document getElementById  memexp   firstChild data   calcval      Stores the new date in a  lt input type  hidden  id  membershipsexpiry date  value    name  membershipsexpiry date  gt  for submission to database table document getElementById  membershipsexpiry date   value   calcval

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Easiest solution is  const todayDate   Date now    return new Date todayDate   1000   60   60   24   30  X     where X is the number of months we want to add

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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   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

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addDateMonate   function  pDatum  pAnzahlMonate         if   pDatum     undefined                 return undefined             if   pAnzahlMonate     undefined                 return pDatum             var vv   new Date         var jahr   pDatum getFullYear        var monat   pDatum getMonth     1      var tag   pDatum getDate         var add monate total   Math abs  Number  pAnzahlMonate           var add jahre   Number  Math floor  add monate total   12 0          var add monate rest   Number  add monate total -   add jahre   12 0           if   Number  pAnzahlMonate    gt  0                 jahr    add jahre          monat    add monate rest           if   monat  gt  12                         jahr    1              monat -  12                      else if   Number  pAnzahlMonate    lt  0                 jahr -  add jahre          monat -  add monate rest           if   monat  lt   0                         jahr   jahr - 1              monat   12   monat                       if     Number  monat       2    amp  amp    Number  tag       29                   if       Number  jahr     400       0          Number  jahr     100    gt  0    amp  amp      Number  jahr     4       0                           tag   29                    else                       tag   28                       return new Date  jahr  monat - 1  tag        testAddMonate   function  pDatum   pAnzahlMonate         var datum js   fkDatum getDateAusTTMMJJJJ  pDatum        var ergebnis   fkDatum addDateMonate  datum js  pAnzahlMonate         app log   addDateMonate        pDatum            pAnzahlMonate               fkDatum getStringAusDate  ergebnis                  test1   function         app testAddMonate   15 06 2010      10        app testAddMonate   15 06 2010     -10        app testAddMonate   15 06 2010      37        app testAddMonate   15 06 2010     -37        app testAddMonate   15 06 2010    1234        app testAddMonate   15 06 2010   -1234        app testAddMonate   15 06 2010    5620        app testAddMonate   15 06 2010   -5120

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This works for all edge cases  The weird calculation for newMonth handles negative months input  If the new month does not match the expected month  like 31 Feb   it will set the day of month to 0  which translates to  quot end of previous month quot   function dateAddCalendarMonths date  months        monthSum   date getMonth     months      newMonth    12    monthSum   12     12      newYear   date getFullYear     Math floor monthSum   12       newDate   new Date newYear  newMonth  date getDate         return  newDate getMonth      newMonth            new Date newDate setDate 0             newDate

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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

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I changed the accepted answer a bit to keep the original date intact  as I think it should in a function like this   x000D   x000D  function addMonths date  months        let newDate   new Date date       var day   newDate getDate        newDate setMonth newDate getMonth      months       if  newDate getDate      day          newDate setDate 0       return newDate    x000D   x000D   x000D

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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   amp  amp   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

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The following function adds months to a date in JavaScript  source   It takes into account year roll-overs and varying month lengths    x000D   x000D  function addMonths date  months    x000D      var d   date getDate    x000D      date setMonth date getMonth      months   x000D      if  date getDate      d    x000D        date setDate 0   x000D        x000D      return date  x000D    x000D   x000D     Add 12 months to 29 Feb 2016 - gt  28 Feb 2017 x000D  console log addMonths new Date 2016 1 29  12  toString     x000D   x000D     Subtract 1 month from 1 Jan 2017 - gt  1 Dec 2016 x000D  console log addMonths new Date 2017 0 1  -1  toString     x000D   x000D     Subtract 2 months from 31 Jan 2017 - gt  30 Nov 2016 x000D  console log addMonths new Date 2017 0 31  -2  toString     x000D   x000D     Add 2 months to 31 Dec 2016 - gt  28 Feb 2017 x000D  console log addMonths new Date 2016 11 31  2  toString     x000D   x000D   x000D      The above solution covers the edge case of moving from a month with a greater number of days than the destination month  eg    Add twelve months to February 29th 2020  should be February 28th 2021  Add one month to August 31st 2020  should be September 30th 2020    If the day of the month changes when applying setMonth  then we know we have overflowed into the following month due to a difference in month length  In this case  we use setDate 0  to move back to the last day of the previous month   Note  this version of this answer replaces an earlier version  below  that did not gracefully handle different month lengths   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

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As demonstrated by many of the complicated  ugly answers presented  Dates and Times can be a nightmare for programmers using any language  My approach is to convert dates and  delta t  values into Epoch Time  in ms   perform any arithmetic  then convert back to  human time       Given a number of days  return a Date object      that many days in the future   function getFutureDate  days             Convert  days  to milliseconds     var millies   1000   60   60   24   days          Get the current date time     var todaysDate   new Date            Get  todaysDate  as Epoch Time  then add  days  number of mSecs to it     var futureMillies   todaysDate getTime     millies          Use the Epoch time of the targeted future date to create          a new Date object  and then return it      return new Date  futureMillies          Use case  get a Date that s 60 days from now  var twoMonthsOut   getFutureDate  60      This was written for a slightly different use case  but you should be able to easily adapt it for related tasks   EDIT  Full source here

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Sometimes useful create date by one operator like in BIRT parameters  I made 1 month back with   new Date new Date   setMonth new Date   getMonth  -1

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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

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var a new Date    a setDate a getDate   5     As above stated method  you can add month to Date function

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I wrote this alternative solution which works fine to me  It is useful when you wish calculate the end of a contract  For example  start 2016-01-15  months 6  end 2016-7-14  i e  last day - 1     lt script gt  function daysInMonth year  month        return new Date year  month   1  0  getDate       function addMonths date  months        var target month   date getMonth     months      var year   date getFullYear     parseInt target month   12       var month   target month   12      var day   date getDate        var last day   daysInMonth year  month       if  day  gt  last day                day   last day            var new date   new Date year  month  day       return new date     var endDate   addMonths startDate  months    lt  script gt    Examples   addMonths new Date  2016-01-01    1      2016-01-31 addMonths new Date  2016-01-01    2      2016-02-29  2016 is a leap year  addMonths new Date  2016-01-01    13      2017-01-31 addMonths new Date  2016-01-01    14      2017-02-28

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All these seem way too complicated and I guess it gets into a debate about what exactly adding  a month  means  Does it mean 30 days  Does it mean from the 1st to the 1st  From the last day to the last day   If the latter  then adding a month to Feb 27th gets you to March 27th  but adding a month to Feb 28th gets you to March 31st  except in leap years  where it gets you to March 28th   Then subtracting a month from March 30th gets you    Feb 27th  Who knows     For those looking for a simple solution  just add milliseconds and be done   function getDatePlusDays dt  days      return new Date dt getTime      days   86400000        or  Date prototype addDays   function days      this   new Date this getTime      days   86400000

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From the answers above  the only one that handles the edge cases  bmpasini s from datejs library  has an issue   var date   new Date  03 31 2015    var newDate   date addMonths 1   console log newDate      VM223 4 Thu Apr 30 2015 00 00 00 GMT 0200  CEST    ok  but   newDate toISOString      2015-04-29T22 00 00 000Z    worse    var date   new Date  01 01 2015    var newDate   date addMonths 3   console log newDate     VM208 4 Wed Apr 01 2015 00 00 00 GMT 0200  CEST  newDate toISOString      2015-03-31T22 00 00 000Z    This is due to the time not being set  thus reverting to 00 00 00  which then can glitch to previous day due to timezone or time-saving changes or whatever     Here s my proposed solution  which does not have that problem  and is also  I think  more elegant in that it does not rely on hard-coded values          param isoDate  string  in ISO 8601 format e g  2015-12-31    param numberMonths  number  e g  1  2  3       returns  string  in ISO 8601 format e g  2015-12-31    function addMonths  isoDate  numberMonths        var dateObject   new Date isoDate           day   dateObject getDate       returns day of the month number         avoid date calculation errors     dateObject setHours 20           add months and set date to last day of the correct month     dateObject setMonth dateObject getMonth     numberMonths   1  0           set day number to min of either the original one or last day of month     dateObject setDate Math min day  dateObject getDate           return dateObject toISOString   split  T   0        Unit tested successfully with   function assertEqual a b        return a     b    console log      assertEqual addMonths  2015-01-01   1    2015-02-01        assertEqual addMonths  2015-01-01   2    2015-03-01        assertEqual addMonths  2015-01-01   3    2015-04-01        assertEqual addMonths  2015-01-01   4    2015-05-01        assertEqual addMonths  2015-01-15   1    2015-02-15        assertEqual addMonths  2015-01-31   1    2015-02-28        assertEqual addMonths  2016-01-31   1    2016-02-29        assertEqual addMonths  2015-01-01   11    2015-12-01        assertEqual addMonths  2015-01-01   12    2016-01-01        assertEqual addMonths  2015-01-01   24    2017-01-01        assertEqual addMonths  2015-02-28   12    2016-02-28        assertEqual addMonths  2015-03-01   12    2016-03-01        assertEqual addMonths  2016-02-29   12    2017-02-28

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This function handles edge cases and is fast   function addMonthsUTC  date  count      if  date  amp  amp  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    gt  d   new Date  2016-01-31T00 00 00Z    Sat Jan 30 2016 18 00 00 GMT-0600  CST   gt  d   addMonthsUTC d  1   Sun Feb 28 2016 18 00 00 GMT-0600  CST   gt  d   addMonthsUTC d  1   Mon Mar 28 2016 18 00 00 GMT-0600  CST   gt  d toISOString    2016-03-29T00 00 00 000Z    Update for non-UTC dates   by A Hatchkins   function addMonths  date  count      if  date  amp  amp  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    gt  d   new Date 2016 0 31   Sun Jan 31 2016 00 00 00 GMT-0600  CST   gt  d   addMonths d  1   Mon Feb 29 2016 00 00 00 GMT-0600  CST   gt  d   addMonths d  1   Tue Mar 29 2016 00 00 00 GMT-0600  CST   gt  d toISOString    2016-03-29T06 00 00 000Z

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d   new Date     alert d getMonth   1     Months have a 0-based index  it should alert 4  which is 5  may

[javascript] JavaScript function to add X months to a date

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