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.

The setMonth() method of Date 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: 3

console.log(event);
// Expected output: "Sat Apr 19 1975 23:15:30 GMT+0100 (CET)"
// Note: your timezone may vary

Syntax

setMonth(monthValue)
setMonth(monthValue, dateValue)

Parameters

monthValue: An integer representing the month: 0 for January, 1 for February, and so on.
dateValue Optional: An integer from 1 to 31 representing the day of the month.

Changes the Date object in place, and returns its new timestamp. If a parameter is NaN (or other values that get coerced to NaN, such as undefined), the date is set to Invalid Date and NaN is returned.

Description

If you do not specify the dateValue parameter, the same value as what is returned by getDate() is used.

If a parameter you specify is outside of the expected range, other parameters and the date information in the Date object are updated accordingly. For example, if you specify 15 for monthValue, 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 the 1st 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.

Because setMonth() 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 using setUTCMonth() or setTime().

If the new local time falls within an offset transition, the exact time is derived using the same behavior as Temporal's disambiguation: "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 transitions
const endOfMonth = new Date(2016, 7, 31);
endOfMonth.setMonth(1);
console.log(endOfMonth); // Wed Mar 02 2016 00:00:00

Specifications

Specification
ECMAScript® 2026 Language Specification # sec-date.prototype.setmonth