Have you ever wondered what what day of the week a holiday or birthday falls on but didn’t have a calendar nearby? Have you ever needed to know what the weekend dates for a particular month are to plan a dinner with friends, but didn’t have your Palm handy? Have you ever needed to know what date the second Tuesday of month falls on, but didn’t have your planner available?

I’m going to show you a neat little “mind hack” that will allow you to match any date with it’s day of the week. If you can memorize 6 numbers (which I’ll help you with) and add numbers up to 7, then you can do this yourself. Let’s get started.

The numbers you need to memorize in order are: 15, 52, 74, 26, 31, and 53. Numbers are inherintly difficult to memorize in and of themselves. The key to memorizing this sequence is to associate them with something more tangible. Sports fans may know players with each of these numbers and be able to imagine them all lined up. If you aren’t a sports fan, some of the numbers may have other value to you: your age, or the age of a friend or loved one; someone’s birth year or the year something notable happened; Messier or NGC object numbers in astronomy; numbers in your social security number, address, or phone number; or any other place they may appear in your life.

Here are a few examples for each:

• 15: the percentage to tip a waiter or waitress, the number of checkers in a side in backgammon
• 52: the number of weeks in a year, the number of playing cards in a deck
• 74: the atomic number of tungsten, Interstate-74 from Iowa to Ohio
• 26: the diameter in inches of a common bicycle tire, the number of letters in the alphabet
• 31: the number of days in August, the number of Baskin-Robbins ice cream flavors
• 53: the number for Herbie, the Love bug, the year Dwight D. Eisenhower became president (‘53)

Note: You can find tons more examples in the integers category in Wikipedia.

Now that you have something meaningful to you for each of these numbers, simply imagine those things in order, for example you might imagine: a backgammon game, a deck of playing cards, a light bulb (for it’s tungsten filament), a bicycle tire, a Baskin-Robbins ice cream cone, and Herbie the Love Bug. Got that? Great!

Now you know the date of the first Sunday of every month in 2006. The first Sunday in January is the 1st (the 1 in 15); the first Sunday in February is the 5th (the 5 in 15). From here, you can calculate any date in your head using simple addition and subtraction. Let’s try a few:

What day does Christmas fall on? Herbie the Love bug is number 53 so the first Sunday in December is the 3rd. The next Sunday is the 10th (just add 7), and the next is the 17th (add 7 more), and the next is the 24th (yet 7 more). We know that Christmas is the 25th and if the the 24th is on a Sunday then Christmas must fall on a Monday.

What day will we vote in November? We know that we vote on the first Tueday after the first Monday. We know that the Herbie’s number is 53 so the first Sunday in November is the 5th. Two days later will be the 7th, which is the first Tuesday after the first Monday, so we will vote on November 7th.

My wife’s birthady is April 27th. What day will that fall on? April is the fourth month so we need our fourth digit. Our second icon is a deck of cards to remind us of the number 52. Therefore the first Sunday in April is the 2nd. I just add 7 to get the next Sundays: 9th, 16th, 23rd. 4 days later, on a Thursday, will be the 27th.

What is the first day of July? July is the 7th month so we need the first number in our 4th icon. We imagine a 26-inch bicycle tire to get that the first Sunday in July is the second. Therefore, July 1st must fall on Saturday.

I don’t know where I learned this little trick, but I picked it up somewhere around ‘97 or ‘98. It’s proven quite useful and it makes for a great little parlor trick among friends who don’t know how easy it really is. Enjoy!