Leap Year Checker
Check whether any year is a leap year.
Enter a year to find out if it’s a leap year — and how many days it has. A year is a leap year if it’s divisible by 4, except for century years, which must be divisible by 400.
Formula / method
Examples
Leap year
Not a leap year
Leap year
The Gregorian leap-year rule
A year is a leap year if it is divisible by 4, with one exception: century years (those ending in 00) are not leap years unless they are also divisible by 400. So 2024 and 2000 are leap years, but 1900 and 2100 are not. When a year qualifies, February gains a 29th day, making the year 366 days long.
Why the extra rules exist
Earth takes about 365.2422 days to orbit the Sun, so a plain 365-day calendar drifts. Adding a day every four years overcorrects slightly, which is why the century exceptions exist: they trim the average to 365.2425 days, keeping the calendar aligned with the seasons for thousands of years. The simple 'divisible by 4' test alone would slowly push the date of the equinox off course. Pair this with our Day of the Week Calculator to see which weekday any February 29 falls on.
Where it's used
- Checking whether a given year has a 29 February
- Validating date logic in software, where leap years are a classic edge case
- Planning an event, contract or birthday around a leap day
- Working out ages for people born on 29 February
- Confirming the number of days in a year for a calculation
Real-world examples
- 2024 is a leap year because it is divisible by 4, so February has 29 days
- 1900 was not a leap year, being a century year not divisible by 400
- 2000 was a leap year because it is divisible by 400
A bit of history
The leap-year rule with its century exceptions came from the Gregorian calendar reform decreed by Pope Gregory XIII in 1582, which also dropped 10 days, so Thursday 4 October was followed directly by Friday 15 October, to realign the calendar with the seasons.
Did you know?
The Gregorian rule of skipping leap years at centuries not divisible by 400 keeps the average year at 365.2425 days, so close to the true solar year that the calendar drifts only about a day over several thousand years.
FAQ
Why isn’t 2100 a leap year?
Century years are leap years only when divisible by 400. 2100 isn’t, so it’s skipped — but 2000 was a leap year.