The leap year rule, explained
A leap year adds one extra day, February 29, to keep our calendar aligned with Earth's orbit around the sun. The rule is simple but has one important exception: a year is a leap year if it's evenly divisible by 4, unless it's also divisible by 100 - in which case it must also be divisible by 400 to still count as a leap year.
Quick examples
- 2024 - leap year (divisible by 4)
- 1900 - not a leap year (divisible by 100, but not by 400)
- 2000 - leap year (divisible by 400)
- 2100 - will not be a leap year
Born on February 29? Our Birthday Calculator and Days Until Birthday tools correctly handle leap-day birthdays in non-leap years.