Leap Year Calculator

Checking a year takes four quick steps. The tool works in two modes, so pick the one that fits your question.

1. Choose "Single year" to check one year, or "Year range" to list and count the leap years between two years.
2. Type the year in the "Year" field, or type the start and end years in the "Start year" and "End year" fields. Use whole years from 1 to 9999.
3. Press Calculate, or press Enter. A single year shows the answer with the divisibility steps, the days in the year, and the next and previous leap years. A range shows the count with the full list of leap years.
4. Press Reset to clear the form and try another year.

A year is a leap year when it divides evenly by 4, unless it also divides evenly by 100, unless it divides evenly by 400 as well. That is the whole rule, and the calculator on this page applies its three tests in order.

The first test is the divide-by-4 test. 2024 passes it because 2024 ÷ 4 = 506 exactly, while 2025 fails because 2025 ÷ 4 = 506.25, which is not a whole number.

The second test is the century exception. 1900 divides evenly by 4, but it also divides evenly by 100, so it is a common year. The third test is the 400-year rescue. 2000 divides evenly by 100 and by 400, so it keeps its leap day and stays a leap year.

The rule exists because a year is not exactly 365 days long. Earth takes about 365.2422 days to orbit the sun, so a plain 365-day calendar drifts about six hours every year.

Adding one day every four years was the Julian calendar's answer, but an average year of 365.25 days runs slightly too long. Those extra 11 minutes a year pushed the calendar about 10 days off by 1582.

The Gregorian reform dropped three leap days every 400 years to fix the drift. That is why century years usually skip the leap day, and why the average Gregorian year is 365.2425 days, very close to the true 365.2422.

The pattern repeats every 400 years, and each cycle holds exactly 97 leap years. 400 years therefore total 146097 days, which divides to an average year of 365.2425 days.

The years 2000 to 2100 hold 25 leap years, from 2000 through 2096 in steps of four. 2100 is skipped because it divides evenly by 100 but not by 400, so the next leap year after 2096 is 2104, an eight-year gap instead of the usual four.

Try the range mode on this page with 2000 and 2100 to see the count worked out with the floor formula. If you were born on February 29, the age calculator shows your exact age in years, months, and days.

The most common error is trusting the divide-by-4 test alone. It correctly flags 2024, 2028, and 2032, but it wrongly flags 1900 and 2100. Always apply the century tests before you call a year a leap year.

Another mistake is mixing up the Julian and Gregorian rules. Under the old Julian rule every fourth year was a leap year with no exceptions, so 1900 would have been one. This calculator uses the Gregorian rule for every year, including years before 1582.

Finally, do not enter year 0. The civil calendar jumps from 1 BC to AD 1 with no year 0 in between, so the calculator accepts whole years from 1 to 9999 and explains the limit if you type 0.

The tool checks the Gregorian leap year rule only. Other calendars use different intercalation rules, so a year that is a leap year here may not be one in the Hebrew or Islamic calendar.

It also does not find the weekday of February 29 or add days across a leap day boundary. To find the weekday of any February 29, use the day of week calculator. To add or subtract days across a leap day, use the date calculator.