If you were born on Leap Day 1920 you would be 100 years old or 25 in Leap Day years. In general terms the algorithm for calculating a leap year is as follows. Leap years have 366 instead of 365 days.
The year must be evenly divisible by 4.
So Which Are and. If a year is divisible by. So Which Are and. Occurrence of the leap year after every four years makes the leap year divisible by 4.