When it's a leap year?

A leap year is a year with 366 days instead of 365; 
every 4 years in February one extra day is added. 

This is done because one year doesn't contain 365 days but 365.25 days. 
By adding once in the 4 years one extra additional day this problem is solved.

Any year that is divisible by 4 is a leap year, such as 2016, 2020, 2024, 2028.

Note: The above rule does not apply to century years.

Centuries such as 1900 and 2000 only have a leap day if they are divisible by 400.
1900 is divisible by 4 and also by 100, but not by 400, so not a leap year.
This means that centuries are only a leap year if they are divisible by 400.

So 1900 is not, 2000 is, 2100, 2200, 2300 is not, but 2400 is another leap year.

2016	February 29, 2016
2020	February 29, 2020
2024	February 29, 2024
2028	February 29, 2028
2032	February 29, 2032
2036	February 29, 2036
2040	February 29, 2040
2044	February 29, 2044
2048	February 29, 2048
2052	February 29, 2052
2056	February 29, 2056
2060	February 29, 2060
2064	February 29, 2064
....