Mental Calendar

Have you seen savants perform ridiculously amazing feats of memory on television? Ever wonder if you too could possess such a prodigious memory? You may not have the potential to be in the World Memory Championships, but there a few simple tricks to go around it.

A trick I have used as a kid to impress adults. Great for livening-up parties. Tell me any date of any year, and I'll tell you the corresponding day.

Just follows these steps:

Formula.
Day(Remainder) = (Year + (Year/4) + Date + M)/7

Substitute M with the value according to the month.
Jan = 0, Feb = 3, Mar = 3, Apr = 6, May = 1, Jun = 4
Jul = 6, Aug = 2, Sept = 5, Oct = 0, Nov = 3, Dec = 5

After dividing by 7, use the Remainder to locate the Day.
Sun = 0, Mon = 1, Tue = 2, Wed = 3, Thur = 4, Fri = 5, Sat =6

Note:

• The year is written as '87 not 1987.
• For (Year/4), ignore the decimal value. There's no need to round it up, cause it's to indicate leap years.
• The values for M are proven to work for dates before year 2000.
• For leap years, minus 1 point from M, regardless before or after 2000.
• For dates that fall on 2000 and after, either (a) minus 1 point from M, or (b) minus 1 point from Remainder
  

Examples:

28th December 1963

Day = (63 + (63/4) + 28 + M)/7
Day = (63 + (15) + 28 + 5)/7
Day = (111)/7

Remainder = 6
Answer is Saturday

14th May 2009

Day = (9 + (9/4) + 14 + M)/7
Day = (9 + (2) + 14 + 1)/7
Day = (26)/7

Remainder = 5

After year 2000,
Remainder - 1 = 4

Answer is Thursday

You have to practice a few times before you can get it right in your head. Just memorize the M values. The above formula is still in the works. If there's any problem with it, please let me know.

Have fun!