Doomsday: February 28 or 29

The last day of the February, either the 28th or the 29th, is known as "Doomsday"

Added 1994-02-22, Updated 2012-02-29

To use the Doomsday Algorithm in any year, we first need to know the Doomsday for that year.

Doomsday is February 28 or 29. In other words, Doomsday is always the last day of February. In normal years, Doomsday is February 28, and in leap years, Doomsday is February 29.

In 2012, which is a leap year, the last day of February is Wednesday the 29th.

Once we know Doomsday, it's pretty easy to get the day of the week for any day in February. This is done by adding and subtracting, using multiples of 7, and you should be comfortable doing this in your head, otherwise the rest of the algorithm will give you trouble! Luckily, most people, through practice or whatever, are good at mentally picturing a month if they have something to anchor it on, and Doomsday is this anchor. For February, it's always the 28th in normal years, and the 29th in leap years.

Example: what was this year's Valentine's Day, February 14th?
Answer: Doomsday 2012 is Wednesday the 29th of February. So one week earlier, the 22nd is also Wednesday. Another week earlier is Wednesday the 15th. So Valentine's Day 2012 is a Tuesday.

Example: what was this year's Groundhog day, February 2nd?
Answer: Doomsday 2012 is Wednesday the 29th... Wednesday the 22nd... Wednesday the 15th... Wednesday the 8th... Wednesday the 1st... So Groundhog Day, February 2nd, is Thursday this year.