WhenMathLeap-Day Span Calculator
Find every February 29 within a date range, using the full Gregorian leap-year rule: divisible by 4, except century years, which must also be divisible by 400.
Worked example
2028 is a leap year (divisible by 4, not a century year), so it has a February 29. 2100 is not a leap year, despite being divisible by 4, because century years need to be divisible by 400 too, and 2100 isn't. 2000 is a leap year, since it is divisible by 400. From January 1, 2027 to January 1, 2029, exactly one leap day falls in range: February 29, 2028.
Why century years are the exception
A simple "every 4 years" rule drifts the calendar out of sync with the solar year by about 3 days every 400 years. Dropping the leap day in century years not divisible by 400 (like 1900 and 2100, but not 2000) corrects that drift, which is why 2000 felt like an exception to an exception.
Limitations
This identifies leap days for calendar purposes only; it is not a legal or actuarial determination for a February 29 birth date.
Frequently asked questions
- Is 2000 a leap year?
- Yes. It's a century year, but it's also divisible by 400, so the exception to the exception applies.