Date Calculator
Add or subtract days from a date, or find the number of days between two dates.
Details
Your Results
What Date Calculator does
Date arithmetic is easy to get wrong by hand because months vary in length and February changes. Deadlines counted on fingers are a common source of off-by-one errors.
This handles both directions: projecting forward or back from a date, and measuring the gap between two.
- Add or subtract a number of days from a date
- Difference between two dates in days, and in weeks and days
- Correct month lengths and leap years
How to use Date Calculator
- 1
Choose the mode
Add, subtract, or find the difference between two dates.
- 2
Enter your dates
Use the date pickers to avoid format ambiguity.
- 3
Read the result
Differences are given in days, and also as weeks plus days.
Limits and known behaviour
- Calendar days only. Business days, weekends and public holidays are not distinguished, which matters for a deadline defined in working days.
- Time zones are not modelled; calculations use plain calendar dates.
- Adding months or years is not offered, only days — which avoids the genuine ambiguity of what one month after 31 January should mean.
- Dates before the Gregorian calendar's adoption are calculated proleptically and will not match historical records.
Privacy and data handling
Runs entirely in your browser
- The calculation runs in this page. Nothing you enter is transmitted or stored.
- The tool works offline once the page has loaded.
Site-wide data handling, including analytics and advertising, is described in the privacy policy.
Frequently asked questions
Does the difference include both end dates?
It counts the days between them, so from the 1st to the 8th is 7 days. If your deadline counts both the first and last day, add one.
Can I count only working days?
No. The calculation covers calendar days, and holidays vary by country and region.