How to Subtract Months From a Date in JavaScript

1. Date getMonth() and setMonth() methods

To subtract months from a date in JavaScript:

1. Call the getMonth() method on the Date to get the months.
2. Subtract the months.
3. Pass the result of the subtraction to the setMonth() method.

For example:

function subtractMonths(date, months) {
  date.setMonth(date.getMonth() - months);
  return date;
}

// August 13, 2022
const date = new Date('2022-08-13T00:00:00.000Z');

const newDate = subtractMonths(date, 3);

// May 13, 2022
console.log(newDate); // 2022-05-13T00:00:00.000Z

Our subtractMonths() function takes a Date object and the number of months to subtract as arguments. It returns the same Date object with the months subtracted.

The Date getMonth() method returns a zero-based number that represents the month of a particular date.

The Date setMonth() method sets the months of a date to a specified zero-based number.

Note: “Zero-based” here means that 0 is January, 1 is February, 2 is March, etc.

If the months subtracted would decrease the year of the date, setMonth() will automatically update the date information to reflect this.

// January 10, 2022
const date = new Date('2022-01-10T00:00:00.000Z');

date.setMonth(date.getMonth() - 2);

// November 10, 2021: year decreased by 1
console.log(date); // 2021-11-10T00:00:00.000Z

In this example, we subtracted 2 months from a date in January 2022. This makes setMonth() automatically roll the year back to 2021.

Avoid side-effects

The setMonth() method mutates the Date object it is called on. This introduces a side effect into our subtractMonths() function. To avoid modifying the passed Date and create a pure function, make a copy of the Date and call setMonth() on this copy, instead of the original.

function subtractMonths(date, months) {
  // 👇 Make copy with "Date" constructor
  const dateCopy = new Date(date);

  dateCopy.setMonth(dateCopy.getMonth() - months);

  return dateCopy;
}

// August 13, 2022
const date = new Date('2022-08-13T00:00:00.000Z');

const newDate = subtractMonths(date, 3);

// May 13, 2022
console.log(newDate); // 2022-05-13T00:00:00.000Z

// 👇 Original not modified
console.log(date); // 2022-08-13T00:00:00.000Z

Tip: Functions that don’t modify external state (i.e., pure functions) tend to be more predictable and easier to reason about, as they always give the same output for a particular input. This makes it a good practice to limit the number of side effects in your code.

2. date-fns subMonths() function

Alternatively, we can use the subMonths() function from the date-fns NPM package to quickly subtract months from a date. It works like our pure subtractMonths() function.

import { subMonths } from 'date-fns';

// June 27, 2022
const date = new Date('2022-06-27T00:00:00.000Z');

const newDate = subMonths(date, 4);

// February 27, 2022
console.log(newDate); // 2022-02-27T00:00:00.000Z

// 👇 Original not modified
console.log(date); // 2022-06-27T00:00:00.000Z

11 Amazing New JavaScript Features in ES13

This guide will bring you up to speed with all the latest features added in ECMAScript 13. These powerful new features will modernize your JavaScript with shorter and more expressive code.