Leap Year Checker
A leap year is a year with 366 days instead of the usual 365, with the extra day added as February 29. The Gregorian calendar rule is: a year is a leap year if it is divisible by 4, except for century years (divisible by 100), which must also be divisible by 400. For example, 2000 and 2400 are leap years, but 1900 and 2100 are not.
Leap years exist to keep the calendar in alignment with Earth's orbit around the Sun, which takes approximately 365.2422 days. Without periodic corrections, the calendar would drift by about 24 days over 100 years, causing seasonal dates to shift significantly. This checker instantly tells you whether any year is a leap year and shows nearby leap years for quick reference.
How it works
A year Y is a leap year if: (Y % 4 === 0 AND Y % 100 !== 0) OR (Y % 400 === 0). Century years must pass the extra divisibility-by-400 test.
Use cases
- Determining whether February 29 exists in a given year
- Planning software date logic that handles leap-year edge cases
- Calculating exact durations between dates across leap years
- Trivia and history research about specific calendar years
- Verifying birthdays and anniversaries that fall on February 29
Frequently asked questions
How do you know if a year is a leap year?
Apply the Gregorian calendar rule: a year is a leap year if it is divisible by 4, unless it is a century year (divisible by 100), in which case it must also be divisible by 400. In code: (Y % 4 === 0 AND Y % 100 !== 0) OR (Y % 400 === 0). For example, 2024 passes (divisible by 4, not by 100) while 2023 does not.
Why is 1900 not a leap year but 2000 is?
Both are century years, so the divisibility-by-4 test alone is not enough — they must also be divisible by 400. 2000 ÷ 400 = 5 exactly, so 2000 was a leap year, but 1900 ÷ 400 = 4.75, so 1900 was not. The same rule makes 2100, 2200, and 2300 common years while 2400 will be a leap year.
Why do leap years exist?
Earth takes approximately 365.2422 days to orbit the Sun, about a quarter day more than the 365-day calendar year. Adding February 29 roughly every four years absorbs that extra time, and skipping three leap days every 400 years (the century rule) fine-tunes the correction. Without it, the calendar would drift by about 24 days every 100 years and the seasons would slide across the calendar.
When is the next leap year?
Leap years fall every four years: 2024 was one, and the next are 2028, 2032, and 2036. The pattern only breaks at century years not divisible by 400 — the next such exception is 2100, which will not be a leap year despite being divisible by 4.
What happens if you are born on February 29?
Your birth date only appears on the calendar in leap years, roughly once every four years. In common years, people born on February 29 typically celebrate on February 28 or March 1, and legal systems differ on which date counts for age milestones. About 1 in 1,461 days is a February 29, making these birthdays quite rare.