Leap Year Calculator
Enter any year to instantly find out whether it's a leap year, along with the next and previous leap years.
How the Leap Year formula works
The Gregorian calendar's leap year rule:
A year is a leap year if: divisible by 4, AND (not divisible by 100, OR divisible by 400)
This three-part rule is what keeps the calendar aligned with Earth's orbit — a plain 'divisible by 4' rule alone would drift over centuries, which is why century years like 1900 are excluded, while 2000 (divisible by 400) is included.
Step-by-step calculation
- Check if the year is divisible by 4 — if not, it's not a leap year.
- If it is divisible by 4, check if it's also divisible by 100.
- If it's divisible by 100, it's only a leap year if it's also divisible by 400.
Worked example
1900: divisible by 4 and by 100, but not by 400 — not a leap year. 2000: divisible by 4, by 100, and by 400 — a leap year. 2024: divisible by 4, not by 100 — a leap year.
Frequently asked questions
Why do century years follow a different rule?
A calendar with a leap year every 4 years with no exceptions would drift by about 3 days every 400 years. Removing 3 leap years per 400-year cycle (the excluded century years) keeps the calendar much more closely aligned with the actual solar year.
How many days does February have in a leap year?
29, instead of the usual 28 — that extra day is what defines a leap year.