Leap Year Calculator: Is It a Leap Year?

How to use the leap year calculator

1. Enter the year you want to test in the first field.
2. Read the result row to see whether it is a leap year and why.
3. Check the next and previous leap year rows for context.
4. Optionally fill in both Range start and Range end to get a separate list of every leap year between two years.

How the leap year rule works

The Gregorian calendar uses a three-part test to decide whether February gets 29 days. A year is a leap year if:

1. It is divisible by 4.
2. But if it is also divisible by 100, it is not a leap year.
3. Unless it is divisible by 400, in which case it is a leap year.

Take 2024 as an example. 2024 divided by 4 equals 506 exactly, so it passes the first test. It is not a century year, so the second test does not apply. Therefore 2024 is a leap year. Now consider 1900: it divides evenly by 4 and by 100, but 1900 divided by 400 is 4.75, so it fails the third test and is not a leap year. The year 2000 passes all three tests because 2000 / 400 = 5 exactly.

Common leap years reference table

This table lists several well-known years and their status according to the leap year checker logic above.

Why we need leap years

A solar year (the time Earth takes to orbit the Sun) lasts roughly 365.2422 days. If calendars used exactly 365 days every year, the seasons would drift by about one day every four years. Adding an extra day every four years compensates for most of that quarter-day fraction, bringing the average calendar year to 365.25 days.

That slight overcorrection (0.0078 days per year) accumulates, which is why the century exception exists. Skipping three leap days every 400 years brings the average to 365.2425 days, close enough that the calendar stays aligned with the seasons for thousands of years. This system was introduced by Pope Gregory XIII in 1582, replacing the older Julian calendar that only used the "divisible by 4" rule.

Using the range feature

Beyond checking a single year, this tool acts as a leap year calculator for entire spans. Enter a start and end year to get a count in the results table and a separate list of every leap year in that interval. The span is limited to 2,000 years to keep the page responsive. This is useful when planning long-term schedules, verifying historical timelines, or building datasets that depend on accurate day counts.

If you need to measure exact durations rather than just identify leap years, pair this tool with a days between dates calculator or a date calculator. For age-related math, a chronological age calculator handles the month and day arithmetic automatically.

Edge cases and common mistakes

People often assume every fourth year is a leap year without exception. The century rule catches many off guard: 1700, 1800, 1900, 2100, 2200 and 2300 are all common years despite being divisible by 4. Only years like 1600, 2000 and 2400 survive the 400-division test.

Negative years (BCE dates) follow the same mathematical rules in the proleptic Gregorian calendar, so year -4 (which historians call 5 BCE) is a leap year. Very large years work identically because the test relies only on modular arithmetic, not on lookup tables. When using this leap year checker, always enter whole integers; fractional years have no meaning in the Gregorian system.

Worked examples