Date.prototype.setMonth()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
ThesetMonth() method ofDate instances changes the month and/or day of the month for this date according to local time.
Try it
const event = new Date("August 19, 1975 23:15:30");event.setMonth(3);console.log(event.getMonth());// Expected output: 3console.log(event);// Expected output: "Sat Apr 19 1975 23:15:30 GMT+0100 (CET)"// Note: your timezone may varySyntax
setMonth(monthValue)setMonth(monthValue, dateValue)Parameters
monthValueAn integer representing the month: 0 for January, 1 for February, and so on.
dateValueOptionalAn integer from 1 to 31 representing the day of the month.
Return value
Changes theDate object in place, and returns its newtimestamp. If a parameter isNaN (or other values that getcoerced toNaN, such asundefined), the date is set toInvalid Date andNaN is returned.
Description
If you do not specify thedateValue parameter, the same value as what is returned bygetDate() is used.
If a parameter you specify is outside of the expected range, other parameters and the date information in theDate object are updated accordingly. For example, if you specify 15 formonthValue, the year is incremented by 1, and 3 is used for month.
The current day of month will have an impact on the behavior of this method.Conceptually it will add the number of days given by the current day of the month to the1st day of the new month specified as the parameter, to return the new date.For example, if the current value is 31st January 2016, calling setMonth with a value of 1 will return 2nd March 2016.This is because in 2016 February had 29 days.
BecausesetMonth() operates on the local time, crossing a Daylight Saving Time (DST) boundary may result in a different elapsed time than expected. For example, if setting the month crosses a spring-forward transition (losing an hour), the difference in timestamps between the new and old date is one hour less than the nominal day difference multiplied by 24 hours. Conversely, crossing a fall-back transition (gaining an hour) result in an extra hour. If you need to adjust the date by a fixed amount of time, consider usingsetUTCMonth() orsetTime().
If the new local time falls within an offset transition, the exact time is derived using the same behavior asTemporal'sdisambiguation: "compatible" option. That is, if the local time corresponds to two instants, the earlier one is chosen; if the local time does not exist (there is a gap), we go forward by the gap duration.
Examples
Using setMonth()
const theBigDay = new Date();theBigDay.setMonth(6);// Watch out for end of month transitionsconst endOfMonth = new Date(2016, 7, 31);endOfMonth.setMonth(1);console.log(endOfMonth); // Wed Mar 02 2016 00:00:00Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-date.prototype.setmonth |