Not exactly its a bit more difficult, leap years occur once every four years unless the year is divisible by 100 and not by 400

so 1900 wasn't a leap year 2000 was one 2100 won't be.

Although in most places I saw the code just ignored it as something that's valid between 1901-2099 is considered good enough in most places.

Edit: sorry shouldn't post this early in the morning, its 400 not 1000