Leap Year Calculator
Check whether a year is a leap year and find the leap years around it.
What the Leap Year Calculator does
A leap year adds 29 February to keep the calendar aligned with the solar year. The rule is divisible by 4, except centuries, except centuries divisible by 400 — which is why 1900 was not a leap year but 2000 was.
Formula
Leap year if (year mod 4 = 0 and year mod 100 ≠ 0) or year mod 400 = 0
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Year | number | Yes | Accepts 1 or more, up to 9999. |
How to use it
- Enter Year.
- Select Calculate.
Worked example
Was 1900 a leap year?
- Year
- 1900
No. It is divisible by 100 but not by 400, so the century exception applies.
Frequently asked questions
Why do we need leap years?
The Earth takes about 365.2422 days to orbit the Sun. Without a correction the calendar would drift by roughly 24 days per century.
Why is 2100 not a leap year?
It is divisible by 100 but not by 400. Adding a leap day every four years overcorrects slightly, and skipping three century leap days per 400 years fixes it.