What is a leap year?
A leap year has 366 days instead of 365, with an extra day added at the end of February: 29 February. Leap years exist because the Earth takes about 365.2422 days to travel around the Sun. Without an extra day every few years, the calendar would slowly drift away from the seasons, by roughly one day every four years and almost a month every century.
How to use the checker
- Type any year to see whether it is a leap year, and why.
- See the previous and next leap years, and the number of days in February and in the year.
- Enter a range to list every leap year in it, for example all the leap years of the 21st century.
The leap year rules
The Gregorian calendar, used by most of the world, has three rules:
- A year divisible by 4 is a leap year,
- except a year divisible by 100, which is not,
- unless it is also divisible by 400, in which case it is a leap year.
leap = (year mod 4 = 0 AND year mod 100 ≠ 0) OR (year mod 400 = 0)
Examples: 2024 and 2028 are leap years (divisible by 4). 1900 and 2100 are not (divisible by 100 but not 400). 2000 was a leap year because it is divisible by 400. These rules give an average year of 365.2425 days, very close to the true solar year.
A bit of history
Julius Caesar introduced a leap day every four years in 46 BC (the Julian calendar). That made the average year slightly too long, and by the 1500s the calendar had drifted by 10 days. In 1582, Pope Gregory XIII introduced the Gregorian calendar with the 100 and 400 rules and removed the extra days. India's official civil calendar uses the Gregorian system alongside the Indian national (Saka) calendar.
Frequently asked questions
Is 2026 a leap year?
No. 2026 is not divisible by 4. The next leap year is 2028.
How many leap years are there in a century?
Usually 24. A century that includes a year divisible by 400, such as 1601–1700 vs 1901–2000, can have 25.
What about people born on 29 February?
They are sometimes called "leaplings". See how the Age Calculator handles their birthdays.