You can use methods in the Date class to subtract dates in JavaScript. The following sections will show these solutions in detail.

Subtract Dates In JavaScript

With getTime()

The getTime() method of a Date instance in JavaScript returns the number of milliseconds that have elapsed since that date to the epoch.

As you may already know, a date in JavaScript is basically defined by the duration between the point in time represented by that object and the epoch. This programming language uses the same epoch as UNIX systems, which is 00:00:00 on 1 January 1970.

var day1 = new Date("12/25/2021");
var day2 = new Date("01/5/2022");
var difference = day2.getTime()-day1.getTime();
var difference_day = difference / (1000 * 60 * 60 * 24);
console.log(difference_day);

Output:

11

The snippet above creates two Date objects with the new keyword and the Date constructor. We carry out a subtraction by invoking the getTime() method for both Date objects. The result is an integer value storing the number of milliseconds between those points in time. To convert it to days, we make a series of divisions and print the result to the console.

Remember that there are several ways to indicate your date with the Date() constructor. In addition to the standard ‘dd/mm/yyyy‘ string, you can also use other formats like this:

new Date(year, monthIndex, day)

Replace the constructors in the example with these, and you will get the same result:

var day1 = new Date(2021, 12, 25);
var day2 = new Date(2022, 1, 5);

To learn more about converting strings to dates in JavaScript, have a look at this guide.

Note that many browsers decide to deliberately reduce the precision of time to improve privacy and security by preventing fingerprinting and timing attacks. The precision of the getTime() gets rounded as a result, depending on the settings.

For instance, Firefox sets this precision to 2ms by default, and you can also change it to 100ms or a bigger value. However, these margins are tiny and should have no impact on the accuracy of your subtraction.

With Date.UTC()

The Date.UTC() method acts like the getTime() method but treats parameters as UTC. Instead of returning a Date object, the method returns the number of milliseconds that have elapsed since that date to the epoch (January 1, 1970, 00:00:00 UTC). It also uses universal time, not local time like the Date() constructor.

This is how you can use the Date.UTC() method to find the differences between two dates in JavaScript:

var day1 = new Date("12/25/2021");
var day2 = new Date("01/5/2022");
var dayutc1 = Date.UTC(day1.getFullYear(), day1.getMonth(), day1.getDate());
var dayutc2 = Date.UTC(day2.getFullYear(), day2.getMonth(), day2.getDate());
var difference = dayutc2 - dayutc1;
var difference_day = difference / (1000 * 60 * 60 * 24);
console.log(difference_day);

Output:

11

Like the Date() constructor, you can use both string and numerical values to specify your date. This means you can rewrite the code above like this:

var dayutc1 = Date.UTC(2021, 12, 25);
var dayutc2 = Date.UTC(2022, 1, 5);

Summary

You can subtract dates in JavaScript by making the calculation based on the same reference – the language’s epoch. Using these absolute durations, which are measured in milliseconds, you can find out the differences between any two days.