I feel I should point out that leap years occur according to the following rule:

The year must be divisible by 4, but not by 100. However the divisible-by-100 rule doesn't apply if the year is also divisible by 400.

So the year 2000 was a leap year, but 1900 was not -- the year 1900 had 365 days. I recommend Wikipedia's Gregorian Calendar article if you want to know more about the Gregorian calendar system.