Leap Year Checker
A leap year isn't simply 'divisible by 4' — there's a century-year exception most people don't know about, which is exactly why the year 2000 was a leap year but 1900 wasn't, despite both being divisible by 100.
Inputs
Result
2026 is not a leap year
February has 28 days
How the leap year checker works
A year is a leap year if it's divisible by 4, EXCEPT century years (divisible by 100), UNLESS that century year is also divisible by 400.
Worked example: checking 2000, 1900, and 2024
- 2000: divisible by 4 AND by 100, but also by 400 → leap year (the 400 exception applies).
- 1900: divisible by 4 AND by 100, but NOT by 400 → not a leap year (the century exception applies, with no 400 override).
- 2024: divisible by 4, not a century year at all → leap year (the simple rule applies directly).
Common mistakes to avoid
Assuming every year divisible by 4 is automatically a leap year
This works for the vast majority of years, but fails specifically for century years not divisible by 400 — 1900 is divisible by 4 but is NOT a leap year, which surprises people who only know the simple 'divisible by 4' rule.
Assuming every century year (like 2100) will be a leap year
The next 'century exception' will actually apply in 2100 — since 2100 is divisible by 100 but not by 400, it will NOT be a leap year, unlike 2000 which was.
Frequently asked questions
Why does the leap year rule have a century exception at all?
A year is about 365.2422 days long, not exactly 365.25 — adding a leap day every 4 years alone slightly overcorrects, so removing 3 leap days every 400 years (via the century exception, with the /400 override) brings the calendar much closer to the true astronomical year length.
When is the next century year that will NOT be a leap year?
2100 — since it's divisible by 100 but not by 400, following the same rule that made 1900 a non-leap year and 2000 a leap year.
How many extra days does February gain in a leap year?
Exactly one — February has 29 days instead of the usual 28, making the full year 366 days instead of 365.
Why does the leap year rule matter beyond just February's day count?
It affects any calculation involving date differences, ages, or schedules that span a leap year, which is why calculators handling dates need this rule built in accurately rather than assuming a fixed 365-day year.
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