Leap year check
No, 3999 is not a leap year.
3999 is not divisible by 4, so it is NOT a leap year, February has the usual 28 days.
A year is a leap year in the Gregorian calendar when it is divisible by 4, with one exception and one exception to that exception: a year divisible by 100 is not a leap year unless it is also divisible by 400. 3999 is not divisible by 4 (3999 ÷ 4 = 999.75), so it cannot be a leap year. The nearest leap years are 3996 before it and 4000 after.
3999 has no February 29, February ends on the 28th. The closest leap day is in 4000, when February 29 falls on a Tuesday. If you are counting toward a leapling birthday or a date-sensitive deadline, that 4000 leap day is the one to watch.
3999 runs 365 days, or 52 full weeks plus 1 day. The leap year before 3999 was 3996 and the next one is 4000, keeping the familiar four-year rhythm. To do date math across 3999, counting days to a deadline, an age, or an anniversary that crosses a leap day, use the days-between calculator, which handles leap days automatically.
Check another year
Type a different year, or count the leap years across a range.
Enter any year from 1582 to 4000.
No, 3999 is not a leap year
3999 is not divisible by 4, so it is NOT a leap year, February has the usual 28 days.
Count leap years in a range
How many leap years fall between two years (inclusive).
Enter a valid from/to range within 1582-4000.