 Do you know what day of the week you were born on?  What about the day of the week you turned 10?  The day you turn/turned 20?  30?  50?  100?  How about the day your parents were born?  Grandparents?  Do you know what day of the week the Declaration of Independance was signed?  Chances are the answer to all of those questions is no.  You may be surprised that there is a mathamatical formula to determine the the answers to those questions.  It takes a bit of memorization and mental math but once you get the hang of it, it is very easy.  You will be well on your way to becoming a human calender

## The Basic Method

The basic method is to find three different numbers: The year code, the month code and the day code.  Somthing that will make this strategy easier is to memorize the multiples of 7:  7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 98, 105, 112, 119 and 126.  You shouldn't need to go any higher then that.

## The Year Code

Let's start with the year code.  The first thing you do is look at the last two digits of the year.  Let's use March 12th, 2009.  The last two digits are 09.  The first thing you do is divide this number by 4.  9 divided by 4 is 2.25.  Ignore the decimals, and add your answer to the original number. 2 plus 9 is 11.  Finally, subtract the highest multiple of 7 you can.  In this case, the number is 7.  9 - 7 = 2.  The year code is two.

Let's do another example.  1962.  That was a long time ago, wasn't it?  62 divided by 4 = 15.5.  Drop the 0.5.  62 + 15 = 77.  Subtract the highest multiple of 7, which is 77.  77 - 77 = 0.  Another important thing to remember are century codes.  1700's is 5, 1800's is 3, 1900's is 1, 2000's is 0 and 2100's is 5.  Since 1962 is in the 1900's, add 1.  0 + 1 = 1.  The year code is one.

## The Month Code

Now the month code.  This is the part that requires memorization.

• Jan - 6*
• Feb - 2*
• Mar - 2
• Apr - 5
• May - 0
• Jun - 3
• Jul - 5
• Aug - 1
• Sep - 4
• Oct - 6
• Nov - 2
• Dec - 4

*If the year is a leap year, subtract 1 from January/February.  The easiest way to see if it's a leap year is to see if the full year is divisible by 4.

Let's go back to our original example, March 12th.  March = 2, so the year code is 2.  If it were June, the month code would be 3.

## The Day Code

Finally, the day code.  This is the easiest part.  The day code is equal to the date.  The code for the 12th would be 12.  The 24th would be 24.  the 1st would be 1, the 8th would be 8, etc.  Easy, right?

## Putting It All Together

Before we try to get our final answer, we must memorize this:

• 1 - Monday
• 2 - Tuesday
• 3 - Wednesday
• 4 - Thursday
• 5 - Friday
• 6 - Saturday
• 7/0 - Sunday

March 12th, 2009.  Year code = 2, Month code = 2, Day code = 12.  2 + 2 + 12 = 16.  Finally subtract the highest multiple of 7.  16 - 14 = 2.  2 = Tuesday.  So, March 12th, 2009 was a Tuesday.

Let's do another example.  Feburary 22, 1924.  24 divided by 4 is 6.  24 + 6 = 30.  30 - 28 is 2.  2 + 1 (Century Code) = 3.  Feb = 1 (Leap Year).  3 (Year code) + 1 (Month code) = 4.  4 + 22 (Day code) = 26.  26 - 21 = 5.  5 = Friday, so February 22, 1924 was a Friday.

## Try It Yourself

Now you try.  The answers are below.

1. January 2nd, 1997
2. June 14th, 1922
3. April 17th, 1774
4. August 4th, 2006
5. December 31st, 2142