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How to calculate the days, weeks and months between two dates

How many days until the deadline? How long was it between two events? How many weeks of notice is that? Counting dates by hand is error-prone — leap years, uneven months, and off-by-one endpoints all catch people out. This guide covers the pitfalls.

The fastest way

Pick a start and end date in the Date Difference Calculator and it shows the gap in days, weeks, months and years at once.

The one thing to decide: inclusive or exclusive

From the 1st to the 5th is 4 days if you count the gaps between them, or 5 days if you count every calendar day including both ends. Neither is "wrong" — a hotel counts nights (exclusive), an event programme counts days (inclusive). Know which you need before you read the number.

Why months and years are approximate

Months range from 28 to 31 days and years include leap days, so a span expressed in months or years is a human-readable approximation while the days figure is exact. The calculator shows all of them so you can pick the right unit for the context.

Related date tools

To measure from a birth date to today specifically, the Age Calculator is purpose-built for that. And if your two dates sit in different time zones, convert them to a common zone first with the Timezone Converter so the day boundaries line up.

A note on privacy

The Date Difference Calculator runs entirely in your browser — nothing is uploaded.

Open the Date Difference Calculator →

Common questions

How do I count the days between two dates?

Subtract the start date from the end date. The subtle part is whether you count both endpoints: from the 1st to the 5th is 4 days if you count the nights between, or 5 days if you count every calendar day inclusive. For deadlines people usually want the exclusive count (how many days away); the calculator shows the gap clearly so you can interpret it either way.

Why isn't a difference in months a whole number of days?

Months have 28–31 days, so '2 months' isn't a fixed number of days. The calculator reports the difference several ways at once — days, weeks, months and years — because which one is 'right' depends on what you're measuring. Days is exact; months and years are the human-readable approximation.

Are leap years handled?

Yes. The calculation uses real calendar dates, so a span that crosses February 29th includes that extra day automatically — you don't need to adjust anything.

Is anything uploaded?

No. The dates you pick are processed entirely in your browser — nothing is sent anywhere.