Calculate any Date!
February 28/29
To start the Doomsday algorithm for any year, you first need to know the Doomsday for that year.
Doomsday is February 28/29, or, 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 2002, the last day of February is Thursday the 28th.
Once you know Doomsday, it's pretty easy to get the day of the week for any day in February. It's done by adding and subtracting, using multiples of 7, and you should be comfortable doing this in your head -- or else 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 for February it's the 28th in normal years, the 29th in leap years.
Example: what is this year's Valentine's Day, February 14th?
Answer: Doomsday 2002 is Thursday the 28th of February. So one week earlier, the 21st is also a Thursday. Another week earlier is Thursday the 14th. So Valentine's Day 2002 is a Thursday.
Example: what is this year's Groundhog day, February 2nd?
Answer: Doomsday 2002 is Thursday the 28th... Thursday the 21st... Thursday the 14th... Thursday the 7th. Now you have to get from the 7th to the 2nd. You could back up five days from Thursday the 7th to reach Saturday the 2nd, but that's pretty awkward. It may be easier to go forward two days fro