When peforming the classic Day of the Week For Any Date feat, it often makes a difference how you do it.

Most performances aim for the instantaneous Rain-Man type of reaction. The required calculations and/or mnemonics can make this challenging, so performers often use various touches than can simultaneously give them time to mentally retrieve the information, while helping, at least in appearance, to speed things up from the audience's point of view.

The year, with its leap year exceptions, is often the hardest part of the date to deal with, so one classic approach is to ask for the year first. Dr. Arthur Benjamin does just this when he performs the calendar feat for audiences:



Recently, another approach was developed that I find interesting. You hand out a book containing perpetual calendars for every year from 1582 to 2399, and as above, you ask for the year first. You then name the page on which they can find the appropriate calendar, and while they look it up, you have time to recall the information about the year. The particular presentation was developed by Hans-Christian Solka, and the prop is available here.

As described, the idea seems to simply be to locate the page as the end of the feat, but I believe it's more effective as a highlight, on the way to giving the correct day of the week. If you click on Preview on that page, you can see the layout of the pages and the table of contents for yourself.

Another angle is to skip a step altogether by eliminating the specific date. Imagine you have a calendar like this printed on the back of your business card. You ask for the month first, then the year, writing them both down on the line to the right of the 31st. After that, you immediately fill out the appropriate days of the week above the dates!

For example, if someone says January for the month, and 2007 for the year, you would fill out the calendar in this way. This approach is especially easy if you're familiar with John Horton Conway's Doomsday approach, and are familiar enough with it to get the doomsday for a given year.

When you're given the month, you simply have to recall the doomsday for that month. In our January 2007 example, as soon as someone says January, you write it down while recalling that the doomsday for January is the 3rd, or the 4th if they name a leap year. Then, when they say 2007, you know that the doomsday for that year is Wednesday (from your calculations or mnemonics), so January 3rd (since 2007 isn't a leap year) is a Wednesday, you simply write “Wednesday” over the 3rd, and write the other days accordingly! This version happens so quickly, that you may want to repeat it, which will also help prove that you're not just guessing at days when checked later.

As a matter of fact, writing down the given date is another tactic often used to make the obtaining of the date appear faster than it is. You can begin your calculations during the writing, especially if someone else is doing the writing, and the audience will often psychologically eliminate the writing time when recalling the feat later. I can't give away too much, but in Paul Brook's The Chrysalis of a Polymath, he has some excellent presentational touches that involve writing it down, and performing it in a way that helps encourage the spectator recall you and your performance long after it is over.

Practice to improve your speed is always essential, of course, but so is staying on top of new developments in calculation. There's an excellent history of development of Doomsday-related techniques here, including the Odd+11 technique I recently discussed. You can find more about techniques at sites like Accelerated Doomsday, An Easier Doomsday Algorithm, First Sunday Doomsday Algorithm and Wikipedia's Doomsday Algorithm page.