files/en-us/web/javascript/reference/global_objects/date/setmonth/index.md

---
title: Date.prototype.setMonth()
short-title: setMonth()
slug: Web/JavaScript/Reference/Global_Objects/Date/setMonth
page-type: javascript-instance-method
browser-compat: javascript.builtins.Date.setMonth
sidebar: jsref
---

The **`setMonth()`** method of {{jsxref("Date")}} instances changes the month and/or day of the month for this date according to local time.

{{InteractiveExample("JavaScript Demo: Date.prototype.setMonth()")}}

```js interactive-example
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

```js-nolint
setMonth(monthValue)
setMonth(monthValue, dateValue)
```

### Parameters

- `monthValue`
  - : An integer representing the month: 0 for January, 1 for February, and so on.
- `dateValue` {{optional_inline}}
  - : An integer from 1 to 31 representing the day of the month.

### Return value

Changes the {{jsxref("Date")}} object in place, and returns its new [timestamp](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#the_epoch_timestamps_and_invalid_date). If a parameter is `NaN` (or other values that get [coerced](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number#number_coercion) to `NaN`, such as `undefined`), the date is set to [Invalid Date](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#the_epoch_timestamps_and_invalid_date) and `NaN` is returned.

## Description

If you do not specify the `dateValue` parameter, the same value as what is returned by {{jsxref("Date/getDate", "getDate()")}} is used.

If a parameter you specify is outside of the expected range, other parameters and the date information in the {{jsxref("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 {{jsxref("Date/setUTCMonth", "setUTCMonth()")}} or {{jsxref("Date/setTime", "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"`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/ZonedDateTime#ambiguity_and_gaps_from_local_time_to_utc_time) 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()

```js
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

{{Specifications}}

## Browser compatibility

{{Compat}}

## See also

- {{jsxref("Date.prototype.getMonth()")}}
- {{jsxref("Date.prototype.setUTCMonth()")}}