How to use Leap Year Calculator
The leap year calculator tells you whether any year is a leap year and shows the details around it. Enter a year and it confirms whether February has 29 days, and lists the previous and next leap years so you can plan ahead or check the past. It applies the full Gregorian rule — divisible by 4, but not by 100 unless also by 400 — so tricky century years like 1900 and 2000 are handled correctly. The calculation runs entirely in your browser.
- Enter a year.
- See whether it is a leap year.
- Check the number of days in February.
- Note the previous and next leap years.
Your data never leaves your device — 100% private processing.
The century-year exception
Most people know the “divisible by 4” part of the leap year rule, but the century exception trips up calendars and code alike. Years ending in 00 are leap years only when divisible by 400, so 2000 was a leap year but 1900 and 2100 are not. This matters because the simple “every four years” rule drifts: it adds a leap day about 0.03 days too often each cycle, which the 100- and 400-year adjustments correct. Software that forgets the exception can miscalculate dates around century boundaries — a class of bug that has caused real scheduling and billing errors. This calculator uses the complete rule, so its answers hold for any year, century boundaries included.
| Year | Divisible by 400? | Leap year? |
|---|---|---|
| 1900 | No | No |
| 2000 | Yes | Yes |
| 2100 | No | No |
Why leap years exist
A calendar year is meant to track the time it takes Earth to orbit the Sun, but that orbit takes roughly 365.2422 days — not a whole number. If we always used 365 days, the calendar would drift about a quarter-day each year, and after a century the seasons would be weeks out of place. Adding one extra day roughly every four years absorbs most of that fraction, and the century-year adjustments handle the small remainder. The result is a calendar that stays locked to the seasons for thousands of years. That is why 29 February exists: it is the periodic correction that keeps spring in March and prevents the calendar from slowly sliding out of sync with the Sun.
Worked examples
Leap
Inputs: 2024
Result: Leap year · Feb has 29 days
Century (no)
Inputs: 1900
Result: Not a leap year
Century (yes)
Inputs: 2000
Result: Leap year
Glossary
- Leap year
- A year with 366 days, including 29 February, used to keep the calendar aligned with the seasons.
- Common year
- An ordinary 365-day year with 28 days in February.
- Century year
- A year ending in 00, subject to the divisible-by-400 rule.
- Gregorian calendar
- The calendar in worldwide civil use, which defines the leap year rules here.
Related reading
Frequently Asked Questions
Why use Leap Year Calculator?
- Instantly checks if a year is a leap year
- Shows how many days February has that year
- Finds the previous and next leap years
- Applies the full century-year rule correctly
Common use cases
- Check whether a birth year or event year was a leap year
- Plan around 29 February for scheduling or billing
- Verify date logic when writing or testing code
- Teach or learn the leap year rules with examples
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