How to Calculate the Number of Days Between Two Dates in JavaScript

 

There are several ways to calculate the number of days between two dates in JavaScript.
While you can do it using native Date objects, I recommend using Moment.js for better accuracy, especially when considering things like daylight saving time, leap years, and timezone complexities.

Let’s go through both approaches!

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1. Using Moment.js (Recommended)

First, install Moment.js if you haven’t:

npm install moment

Now, you can easily calculate the difference in days:

const moment = require('moment');

let start = moment("2013-11-03");
let end = moment("2013-11-04");

let diff = end.diff(start, "days");

console.log(diff); // Output: 1

✅ Explanation:

• moment(dateString) creates a Moment date object.

• .diff() calculates the difference between two dates.

• The second parameter "days" specifies the unit of time to return.

Bonus:
Moment.js handles complexities like daylight saving time out of the box!

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2. Using Plain JavaScript (No external libraries)

If you want to avoid dependencies, you can use plain JS:

let start = new Date("2013-11-03");
let end = new Date("2013-11-04");

let diffTime = Math.abs(end - start);
let diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));

console.log(diffDays); // Output: 1

✅ Explanation:

• new Date() creates a native date object.

• Subtracting dates returns the difference in milliseconds.

• Divide by 1000 * 60 * 60 * 24 to convert milliseconds to days.

• Math.ceil() rounds up to ensure you count any partial days as full days.

⚠️ Note: Plain JavaScript works well for simple use cases but does not handle timezones and daylight saving time as gracefully as Moment.js.

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Conclusion

Method	Pros	Cons
Moment.js	Easy, reliable, handles edge cases (DST, timezones)	Requires external library
Plain JavaScript	No dependencies, lightweight	Manual calculations, watch out for DST issues

If your application is date-heavy (calendars, scheduling apps, etc.), go with Moment.js or modern libraries like date-fns.
For simple scenarios, native JavaScript is perfectly fine.