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## Day For Any Date in 2011

Published on Thursday, January 06, 2011 in , , , ,

How would you like to be able to know the date for any day in 2011? Here's how to do it!

The method to do this is quite simple, and is known as the Doomsday method, originally developed by John Horton Conway. Don't worry, learning this method for one particular year is very simple.

The "Doomsday" from which the method gets its name always refers to the last day of February, whether it's the 28th or 29th. For 2011, the "Doomsday" is Monday (Feb. 28th, since it's not a leap year). If you think about it, you can already work out any date in February using just this knowledge.

For example, Valentine's Day, Feb. 14th, must also be a Monday, because it's exactly 2 weeks before Feb. 28th. How about Feb. 2nd (Groundhog Day)? Well, Feb. 7th is a Monday, and Feb. 2nd is 5 days before that. What's 5 days before a Monday? The answer is Wednesday! Therefore, Groundhog Day will be on Wednesday in 2011.

It's also fairly simple to learn the even-numbered months. There's a very simple pattern to remember them: 4/4 (April 4th), 6/6 (June 6th), 8/8 (August 8th), 10/10 (October 10th), and 12/12 (December 12th) will always fall on the same day of the week as the "Doomsday" (the last day of February, remember?).

On which day will Christmas fall in 2011? We know December 12th is a Monday, so 2 weeks later, December 26th, is also a Monday. Since Christmas is one day before that, it must be on a Sunday this year!

The odd months aren't much harder, but the patter is not the same. 5/9 (May 9th) and 9/5 (September 5th) will also always fall on the Doomsday, as will 7/11 (July 11th) and 11/7 (November 7th). This is easy to remember with the following simple mnemonic: "I'm working 9 to 5 at the 7-11". It helps you remember that 9 and 5 always go together, as do 7 and 11.

When is July 4th this year? It's exactly 1 week before July 11th, so it must be a Monday, as well. If you've got all the previous dates down, you've already got the mental capability to determine the date for 10 out of the 12 months!

The easiest way to handle March is to think of Feb. 28th as also being "March 0th". Working forward from March 0th, it's easy to see that March 7th, 14th, 21st and 28th will all be Sundays. St. Patrick's Day, March 17th, is 3 days after March 14th, so it's 3 days after a Monday, making it a Thursday in 2011.

In January, it's usually the 3rd day of the month that falls on the Doomsday. In a leap year, however, January 4th falls on the Doomsday. Remember it this way: "3 times out of 4, it's January 3rd. On the 4th year, it's January 4th." In 2011, since it's not a leap year, you only have to remember that January 3rd falls on the Doomsday (Monday, for 2011).

January 15th is Martin Luther King, Jr.'s birthday, but what day does it fall on in 2011? January 3rd is a Monday this year, and so is January 17th (2 weeks later). Take back 2 days, and we get January 15th being a Saturday this year!

With the above knowledge, and a little practice, you can quickly and easily determine the day of the week for any 2011 date. You could get practice at the Day For Any Date (Mentalist Challenge) page, changing the year to 2011, and then trying to determine the date before you click the Show button.

When you're demonstrating this ability for someone, it's nice to be able to prove that you're right about the date. I use QuickCal on my iPod Touch (similar calendar are available for many portable devices). If you prefer a non-electronic version that's portable, download and print the 2011 Thumb Calendar.

If you have any experiences or thoughts you'd like to share about memorizing the 2011 calendar, I'd love to hear about them in the comments!

### 1 Response to Day For Any Date in 2011

Anonymous
9:29 AM

The easiest way to handle March is to think of Feb. 28th as also being "March 0th". Working forward from March 0th, it's easy to see that March 7th, 14th, 21st and 28th will all be Sundays. St. Patrick's Day, March 17th, is 3 days after March 14th, so it's 3 days after a Monday, making it a Thursday in 2011.

March 7,14,21,28 will all be Mondays instead of Sundays.