A calendar year is typically 365 days long. However, it takes the Earth approximately 365.2422 days to orbit the Sun. To make up for this discrepancy, we add an extra day to the calendar every four years, creating a leap year of 366 days.
The Three Rules of Leap Years
- The year must be evenly divisible by 4.
- If the year is divisible by 100, it is NOT a leap year, UNLESS...
- The year is also divisible by 400. In that case, it is a leap year.
For instance, the year 2000 was a leap year because it is divisible by 400. However, 1700, 1800, and 1900 were not leap years because they were divisible by 100 but not 400.