Doomsday algorithm

The Doomsday algorithm for calculating the day of the week makes use of the fact that in each year, April 4th (4/4), June 6th (6/6) August 8th (8/8), October 10th (10/10) and December 12th (12/12) are all the same day of the week. This day of the week is called Doomsday. The name makes the algorithm sound more dire than it is. It’s really just a trick to make it easy to calculate the day of the week for any day by knowing the day of the week for one day in each month. The algorithm was invented by John Conway, also known for the Game of Life.