First Sunday Doomsday Algorithm

A method for finding the day of the week for any date -- in your head.

Thursday, May 3, 2018

New Perpetual Calendar

Here is a One-page 200-year calendar, which I designed after buying and trying a device that I found on AliExpress ("Portable 50 years perpetual calendar keyring").

The device turned out to be useless -- too small to read, and not much like a calendar even if you could see it. Fortunately it only cost me $1.04, including shipping from China.

I decided to try for something better and cheaper -- using my "doomsday" knowledge -- and this is the result.

Please print it out and try it. It will only cost you one sheet of paper. After you set the "sliding window", you can fold it (in thirds, like a letter), and hold it with paperclips.

And here is the Perpetual version of the one-page calendar.  It has a separate piece for selecting the century, so it's a little complicated compared to the simple sliding window above.

Thursday, January 27, 2011

Learn by Example

[Revised 7/29/2011]
This quick summary will show you, by example, how to determine the day of the week for any date.

Wednesday, December 2, 2009

Learn the First Sunday Doomsday Algorithm

[Revised 8/17/2011]
This longer article will show you how to determine the day of the week for any given date -- without consulting a calendar. It covers some history (of calendars and methods) and explains how this method works, and why it works.