Leap Year Checker

What this tool does

Leap Year Checker applies the full Gregorian leap year rule, divisible by 4, except century years, which must be divisible by 400, to any year and reports whether it is a leap year, which rule decided it, how many days February and the year have, and the nearest previous and next leap years.

The leap year rule sounds simple, divisible by 4, until the century exception comes up: century years like 1900 and 2100 are not leap years despite being divisible by 4, while the exceptional-exception year 2000 was a leap year because it’s divisible by 400. Remembering all three layers of the rule correctly is where most people get it wrong.

This checker applies the full three-layer Gregorian rule to any year you enter: divisible by 4 is a leap year, unless it’s also divisible by 100, in which case it is not, unless it’s also divisible by 400, in which case it is after all. The result explicitly states which layer of the rule decided the answer, plus February’s day count, the year’s total day count, and the nearest previous and next leap years for context.

How to use Leap Year Checker

1. Enter the Year you want to check.
2. Read the Is it a leap year? result.
3. Check Days in February (28 or 29) and Days in the year (365 or 366).
4. Read the explanation of which rule layer applied.
5. Check the Previous leap year and Next leap year for context.

Tips for better results

• Century years are the trap: a year divisible by 100 is a leap year only if it’s also divisible by 400, which is why 1900 and 2100 are not leap years but 2000 was.
• Leap years occur roughly every 4 years, but century exceptions mean the actual long-run average is 365.2425 days per year, not exactly 365.25.
• This uses the modern Gregorian rule throughout, even for years before 1582 when the Gregorian calendar was not yet historically adopted; it is not a historical calendar simulator.
• The next and previous leap year results are useful for sanity-checking date-math tools that clamp 29 February dates.

Common use cases

• Checking whether a specific year has a 29 February for scheduling or date-of-birth purposes.
• Teaching or reviewing the full three-layer Gregorian leap year rule, including the century exception.
• Verifying the day count of a year for payroll, interest or other day-based financial calculations.
• Finding the nearest leap years around a given year for planning a 29 February event.

Common mistakes to avoid

• Applying only the "divisible by 4" rule and forgetting the century exception, which incorrectly flags 1900 or 2100 as leap years.
• Forgetting the exception-to-the-exception: century years divisible by 400, like 2000, are leap years despite being divisible by 100.
• Treating this as a historical calendar checker; it always applies the modern Gregorian rule, not the Julian calendar that was actually in use before 1582 in most of Europe.