## Leap years algorithm.

### 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:

- 1) A leap year is evenly divisible by 4

(remainder is zero when divided by 4). - 2) Except if it is evenly divisible by 100 then it isn't a leap year.
- 3) Except if it is evenly divisible by 400, then it's a leap year.

## How often do the leap years occur in the calendar?

### Nearly once every four years, more exactly, 97 leap years at every 400 years.

Nearly once every four years is a leap year, and these years must be multiples of 4. More precisely, as we can calculate above, leap years happen in a cycle of 97 years out of every 400.

## Examples of leap years.

- Examples of leap years which are multiples of 4 but not of 100 nor of 400: 1584, 1588, 1596, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2004, 2008, 2012, 2016, 2020, 2024, 2028, etc.
- Examples of common years (NOT LEAP YEARS), which are multiples of 100, but not of 400: 1700, 1800, 1900, 2100, 2200, 2300 - these are not leap years.
- Example of leap years which are multiples of 400: 1600, 2000, 2400.