How to Check If a Year Is a Leap Year (The Rules and Why They Exist)
Learn the three leap year rules, see examples such as 2000 and 2100, and find the next leap years, with the astronomy behind the extra day.
Every four years February gets an extra day, but not always. The year 2000 was a leap year, while 1900 and 2100 are not. The rule has three parts, and knowing them is useful for programmers, teachers and anyone planning a date far ahead. The free Leap Year Checker answers instantly and explains why.
Quick answer
A year is a leap year if it is divisible by 4, except for years divisible by 100, unless they are also divisible by 400. So 2024 is a leap year, 2100 is not, and 2000 was.
The Leap Year Checker with a year entered.
The three rules in order
- If the year is divisible by 400, it is a leap year. (2000, 2400)
- Otherwise, if it is divisible by 100, it is not a leap year. (1900, 2100, 2200)
- Otherwise, if it is divisible by 4, it is a leap year. (2024, 2028, 2032)
- All other years are not leap years.
Examples
| Year | Divisible by 4 | by 100 | by 400 | Leap year? |
|---|---|---|---|---|
| 2024 | yes | no | no | Yes |
| 2026 | no | no | no | No |
| 2100 | yes | yes | no | No |
| 2000 | yes | yes | yes | Yes |
After 2026, the next leap years are 2028, 2032, 2036 and 2040.
Why do we need leap years?
The Earth takes about 365.2422 days to go around the Sun. A calendar of exactly 365 days would drift by almost six hours each year, and the seasons would slip against the dates. Adding one day every fourth year corrects most of it. The century rule removes three leap days in every 400 years, because adding a day every four years slightly overcorrects. The result is an average year of 365.2425 days, which is accurate to about one day in 3,000 years.
What a leap year changes
- February has 29 days, and the year has 366 days.
- A person born on 29 February has a birthday every four years. Many countries treat 28 February or 1 March as the legal birthday in other years.
- Annual salaries, interest and rent can be calculated by days, and the extra day matters.
- Software that assumes 365 days can break on 29 February. Always use a tested date library.
Other calendars
The Bangla calendar in Bangladesh was reformed to line up with the Gregorian one, so that Pohela Boishakh falls on 14 April, and it adds a day to Falgun in a leap year. The Hijri calendar is lunar and has its own leap years, about 11 in every 30 years. You can convert dates with the Bangla Date Converter and the Hijri Date Converter.
Frequently asked questions
Is 2100 a leap year? No. It is divisible by 100 but not by 400.
When was the last leap year?
- The next is 2028.
How many days are in a leap year? 366, and February has 29.
Can I rely on "divisible by 4" alone? Only for the years from 1901 to 2099. Outside that range the century rule matters.
Next step
Test any year in the Leap Year Checker. Count days between dates with the Date Difference Calculator.
