Add hours to a date in JavaScript

The setTime() and getTime() methods of the Date object can be used to increment or decrement hours from a date in JavaScript.

The following example demonstrates how you can add 3 hours to the current date:

const today = new Date()
const afterThreeHours = new Date()

// Add 3 Hours
afterThreeHours.setTime(today.getTime() + 3 * 60 * 60 * 1000)

The getTime() method returns the number of milliseconds elapsed between January 1st, 1970, at 00:00:00 UTC and the given date.

The setTime() method takes a number representing the milliseconds since January 1st, 1970, at 00:00:00 UTC and sets the value on the given date.

You can also update the existing JavaScript Date object as shown below:

const date = new Date()
date.setTime(date.getTime() + 3 * 60 * 60 * 1000)

To subtract hours from a date in JavaScript, simply minus the number of milliseconds when updating the date with the setTime() method:

const today = new Date()
const lastHour = new Date()

// Minus 1 Hour
lastHour.setTime(today.getTime() - 1 * 60 * 60 * 1000)

Finally, if you are frequently manipulating dates in JavaScript, add a function to Date’s prototype and call it directly whenever you want to add or subtract hours:

Date.prototype.addHours = function (hours) {
  const date = new Date(this.valueOf())
  date.setTime(date.getTime() + hours * 60 * 60 * 1000)
  return date
}

// Add 1 Hour
const nextHour = new Date(2022, 10, 15)

console.log(nextHour.addHours(1))
// Tue Nov 15 2022 01:00:00 GMT+0500 (Pakistan Standard Time)

// Minus 1 Hour
const lastHour = new Date(2022, 10, 15)

console.log(lastHour.addHours(-1))
// Mon Nov 14 2022 23:00:00 GMT+0500 (Pakistan Standard Time)