In this guide
A leap year has 366 days instead of 365, with an extra day, 29 February, added to keep the calendar in step with the seasons. It matters more than it seems: leap years affect ages, deadlines, contracts and every calculator that counts days.
Why leap years exist
The Earth takes about 365.2422 days to orbit the Sun, not exactly 365. If the calendar ignored the extra fraction, it would drift by roughly one day every four years, and after a few centuries the seasons would fall in the wrong months. Adding one day every four years fixes most of the gap.
The leap year rule
The Gregorian calendar, which most of the world uses, has three rules:
- A year divisible by 4 is a leap year.
- Unless it is divisible by 100, in which case it is not.
- Unless it is also divisible by 400, in which case it is.
That is why 2000 was a leap year but 1900 and 2100 are not. Over 400 years this gives 97 leap years and an average year of 365.2425 days, very close to the real value.
| Year | Leap year? | Reason |
|---|---|---|
| 2024 | Yes | Divisible by 4 |
| 2026 | No | Not divisible by 4 |
| 2028 | Yes | Divisible by 4 |
| 1900 | No | Divisible by 100 but not by 400 |
| 2000 | Yes | Divisible by 400 |
| 2100 | No | Divisible by 100 but not by 400 |
A short history
The Romans under Julius Caesar introduced a leap day every four years in 45 BC. That Julian calendar was slightly too long, and by the 16th century it had drifted by about ten days. In 1582 Pope Gregory XIII introduced the refined rule above and ten days were skipped to catch up. Some countries adopted the new calendar centuries later than others.
Leap day birthdays
About 1 in 1,461 people is born on 29 February, because a four-year cycle contains 1,461 days. People born on this day are sometimes called leaplings. In other years they celebrate on 28 February or 1 March, and the rules for legal purposes such as driving ages differ by place. Our age calculator counts 1 March as the birthday in non-leap years.
How leap years change date math
- The span from 1 January to 1 January is 366 days when it includes 29 February.
- Adding one year to 29 February lands on a date that does not exist, so tools move it to 28 February or 1 March.
- The gap from 28 February to 1 March is 2 days in 2024 but 1 day in 2025.
When is the next leap year?
After 2024 the next leap years are 2028, 2032 and 2036. A quick check: if the year divides by 4 with no remainder, and is not a century year unless it divides by 400, it is a leap year.
Try the calculators
- Date Calculator: Add or subtract days from a date
- Days Between Dates Calculator: Count days, weeks and weekdays
- Age Calculator by Date of Birth: Exact age, total days lived, next birthday
General information only, not professional advice. See our editorial policy.