Leap Year Calculator
Check any year for leap status, February days, and next leap year.
What it does
The Gregorian calendar keeps 365 day years near the solar year by adding February 29 almost every fourth year. Without the fix the calendar would drift about a day every four years against the seasons.
The tool above checks any year 1 to 9999. It returns leap or common status, February length, and the next leap year. The default 2024 is a leap year with 29 day February and next leap 2028.
The rule has three clauses: divisible by 4 is leap, except century years, which must divide by 400. National timekeeping and eclipse references state it identically, with 2000 as leap and 1900 plus 2100 as common, on a 400 year cycle of 146,097 days.
February carries the whole adjustment. Leap Februaries hold 29 days while common ones hold 28, and every other month ignores the cycle entirely.
How to use
- Type a year from 1 to 9999.
- Read leap or common first.
- Read February days beside it.
- Use next leap for planning birthdays and events.
- Test centuries separately: 2000 yes, 1900 no, 2100 no.
- Pair with a weekday page for the exact Feb 29 date.
Formula
- % 4
- Basic four year leap test.
- % 100
- Century exception that cancels most century leaps.
- % 400
- Exception to the exception that restores years like 2000.
Proleptic years before adoption use the same arithmetic. Year 0 in astronomical counting divides by 400, so it reads leap.
Worked example
Example: 2024
Default input: 2024.
- Divide by 4: 2024 / 4 = 506 exactly, so candidate leap.
- Century test: 2024 % 100 is 24, not a century, no exception.
- Verdict: leap year with 29 day February.
- Next: 2025, 2026, 2027 fail the 4 test, 2028 passes.
- Spot checks: 2000 divides by 400, leap; 1900 and 2100 do not, common.
- Tool shows Leap year, 29 days, Next leap 2028.
Reference table
| Year | Verdict | Why |
|---|---|---|
| 1896 | Leap | Divides by 4, no century issue |
| 1900 | Common | Century not divisible by 400 |
| 1904 | Leap | Divides by 4 |
| 2000 | Leap | Century divisible by 400 |
| 2024 | Leap | Divides by 4 |
| 2025 | Common | Remainder 1 on division by 4 |
| 2100 | Common | Century not divisible by 400 |
| 2400 | Leap | Century divisible by 400 |
Limits
- Gregorian rules only; other calendars differ.
- Proleptic before local adoption, not historical use.
- Years bound 1 to 9999 for display sanity.
- No weekday output; pair with a weekday page.
Common mistakes
- Calling every divisible by 4 year leap, including 1900.
- Calling 2000 common because it is a century.
- Giving February 29 days in common years.
- Placing Feb 29 in March math.
- Assuming adoption year was universal.
Try it yourself
Quick checks. Answers sit tucked under each question.
2000 leap or common?
Leap: divisible by 400, February 29 days.
1900 leap or common?
Common: century not divisible by 400, next leap 1904.
2100 leap or common?
Common: next leap 2104.
Questions
Is 2024 a leap year?
Yes. February had 29 days and next leap is 2028.
Is 2025 a leap year?
No. It is common with 28 day February.
Was 2000 a leap year?
Yes. Centuries divisible by 400 stay leap.
Is 2100 a leap year?
No. Centuries must divide by 400, and 2100 leaves 100.
How long is the Gregorian cycle?
400 years exactly, 146,097 days, mean year 365.2425 days.
Why February?
Roman calendar history left February the short month, so it hosts the extra day.