Links to resources on the Web for additional information about the Doomsday Algorithm
Added 1997-08-29, Updated 2013-02-28
The following web sites are about or include descriptions of Dr. Conway's Doomsday algorithm.
What Day Is Doomsday? How to Mentally Calculate the Day of the Week for Any Date, October 2011 article in Scientific American.
The Second Doomsday Lesson describes a 2010 meeting with Dr. Conway in which he explains the "Hand" method on the back of a napkin (picture included).
Doomsday Rule, by S. W. Graham, includes substantial explanations, plenty o' exercises, and examples; also available in PDF format.
Simon Cassidy comments on the "Hand" in the context of the Dee-Cecil calendar.
C.07.2 Can I calculate the date of Easter? explains Conway's algorithm for Easter, and gives another explanation of his Doomsday algorithm; includes the remark "Note to non-US readers: 'Seven-Eleven' is the name of a ubiquitous chain of convenience stores." Reader Richard Ezell wrote to me in 2004 to report that this explanation may not really be necessary, as he had seen four 7-11 stores in a seven block stretch in Bangkok, Thailand.
AST 309-TIME; What is the day of the week, given any date? contains notes by William H. Jefferys for a school course on time, with another explanation of the Doomsday algorithm (examples are from 1997).
The Doomsday Rule for Fortnights, by Jim Blowers, gives calculations for Doomsday based on 14-day periods.
Kate Larson's Mathematical poem to calculate the "day of the week" for any day of any year is a beautiful, whimsical poem, attributed to Dr. Conway, which describes the algorithm completely, including both Gregorian and Julian century adjustments. (Note: link goes to archive.org, as the original has dropped off the Web.)
Any Day of the Week Using the Doomsday Rule, by Paul J. Weiss, is a C++ implementation with downloadable code.
For more information about Dr. Conway, see:
Not Just Fun and Games April 1999 Scientific American profile of John H. Conway. (Note: this article is now available online only if you purchase the digital edition.)
Charles Seife's Mathemagician -- an amusing article about John Horton Conway.
John Conway's Game of Life by Stephen Stuart -- an interactive version that you can play via your web browser.
For links to other calendar sites, see my Calendar Links page.
The Doomsday Algorithm was "latest link in the braid" for the week of April 6-12, 1999.
"This page will teach you a simple algorithm to calculate mentally the day of the week corresponding to any given date. Give it a try, it's quite rewarding! The page features clear instructions, examples, and mnemonic tricks."
KaBoL is a "cool math site of the week" service to the mathematics community provided by the Canadian Mathematical Society.