A leap year has 366 days, one extra day (Feb 29) over a normal year. Nearly every 4 years is a leap year (97 leap years every 400 years)
Is it a leap year? Last leap year before & next leap year after this year
The leap year algorithm. The three conditions to check in order to know whether a year is a leap or a common one:
1) A leap year is divisible by 4 (evenly divided by 4, having a zero remainder when divided by 4)
2) Except if it's divisible by 100 (evenly divided by 100, having a zero remainder when divided by 100) then it isn't a leap year
3) But even for the previous step above, if it's also divisible by 400 (evenly divided by 400, having a zero remainder when divided by 400) then it's a leap year
Every year that is evenly divisible by 4 is a leap year, except for years that are evenly divisible by 100, but these years are leap years if they are evenly divisible by 400:
Examples of leap years.
Leap years multiples of 4 but not of 100 nor of 400: 1992, 1996, 2004, 2008, 2012, 2016, 2020, 2024, 2028;
Common years (NOT LEAP YEARS) multiples of 100, but not of 400: 1700, 1800, 1900, 2100, 2200, 2300;