A leap year has 366 days instead of 365, adding 29 February to keep the calendar synchronised with Earth’s orbit. This checker tells you instantly whether any year — past or future — is a leap year or a common year, explains exactly which rule decided it, and shows the next leap year. It is handy for scheduling, date arithmetic, history questions and anyone born on 29 February.
How it works
The tool applies the Gregorian leap-year rule, which is a single boolean expression:
A year is a leap year if it is divisible by 4 AND not divisible by 100 — OR if it is divisible by 400.
In order of precedence the checker tests:
- Divisible by 400 → leap year (e.g. 2000)
- Otherwise divisible by 100 → common year (e.g. 1900, 2100)
- Otherwise divisible by 4 → leap year (e.g. 2024)
- Otherwise → common year (e.g. 2023)
The century corrections matter because Earth’s orbit is about 365.2422 days, not a clean 365.25. Adding a day every 4 years overcorrects slightly, so three leap days are removed every 400 years.
Reference table
| Year | ÷4? | ÷100? | ÷400? | Result |
|---|---|---|---|---|
| 2024 | Yes | No | — | Leap (366 days) |
| 2023 | No | — | — | Common (365 days) |
| 1900 | Yes | Yes | No | Common (365 days) |
| 2000 | Yes | Yes | Yes | Leap (366 days) |
| 2100 | Yes | Yes | No | Common (365 days) |
| 2400 | Yes | Yes | Yes | Leap (366 days) |
Why the century exception trips people up
The intuition that “every 4 years = leap year” is almost right — but century years break it. The year 1900 was not a leap year, even though it is perfectly divisible by 4. The same will be true of 2100, 2200 and 2300. The year 2000, by contrast, was a leap year because it satisfies the ÷400 override.
This matters practically: anyone building date-handling code, or planning schedules that cross a century boundary (contracts, recurring events, financial projections) should test year 2100 explicitly. Many software implementations that only check divisibility by 4 will incorrectly add a day in 2100.
Edge cases and uses
Born on 29 February? People born on leap day often celebrate on 28 February or 1 March in common years. Check any year with this tool to know whether their actual birth date exists in a given year.
Date arithmetic across leap boundaries. If you are counting days between two dates that span February, whether the intervening years are leap or common can shift the total by one day per leap year in the range.
Historical calendars. The Gregorian calendar was introduced in 1582, replacing the Julian calendar (which had a simpler every-4-years rule with no century exception). Years before 1582 in many countries followed the Julian system, so the leap year rule is different for historical dates. This tool applies the Gregorian rule.
The check is pure local arithmetic in your browser — nothing is uploaded or stored.