Simon Willison’s Weblog

The Doomsday Algorithm

I always thought you had to be an idiot savant to be able to state the day of the week for any date in history, but it turns out there’s a reasonably simple trick to it. The Doomsday Algorithm was first invented by Dr John Conway, also famous for creating the game of life. Rudy Limeback’s detailed explanation provides everything you need to know about the algorithm, how it works and how to memorise it.