What Is a Leap Year and Why Does It Exist?
Last updated 2026-09-12
A leap year adds an extra day (February 29) to keep our calendar synchronized with Earth's actual trip around the sun.
Learn the basic rule
A year is a leap year if it's divisible by 4.
Learn the century exception
Century years (1900, 2000, 2100...) are leap years only if divisible by 400 — so 2000 was a leap year, but 1900 and 2100 are not.
Example
2024 is a leap year (divisible by 4). 1900 is not (divisible by 100, not 400). 2000 is a leap year (divisible by 400).
Important Considerations
- Earth actually takes about 365.2422 days to orbit the sun — the leap year rule approximates this without needing fractional days.
- Without leap years, the calendar would drift by about a day every 4 years, eventually putting summer months in what should be winter.
- The century exception exists because 365.25 (the simple 4-year rule) is very slightly more than the true value, so 3 leap years are skipped every 400 years to correct for it.
Frequently Asked Questions
- How often do leap years happen?
- Every 4 years, except century years not divisible by 400 — so 97 times every 400 years, not exactly 100.
- What happens to people born on February 29?
- They typically celebrate on February 28 or March 1 in non-leap years, depending on personal or legal convention.