How to use
Enter a whole four-digit-style year from 0001 through 9999 and select Calculate. The result states the year type and exact day count.
Gregorian leap-year formula
A year is leap if it is divisible by 4, except century years must also be divisible by 400. Thus 2024 and 2000 are leap years, while 1900 and 2100 are common years.
Scope and limits
The calculation uses the proleptic Gregorian rule for the entire supported range. It does not reproduce each country’s historical switch from Julian to Gregorian calendars or decide legal calendar questions.
Frequently asked questions
Why was 2000 a leap year but 1900 was not?
Both are century years, and only 2000 is divisible by 400.
How many days are in a leap year?
366 days, because February has 29 days.
Does every fourth year work?
Not by itself; the century exception and 400-year rule also apply.