Formula for determining the day of a given date?

[Boogers]

Is there a simple, easy-to-memorize-and-apply formula and/or mnemonic for determining the day of the week that a particular date fell on?

Obviously, there are ways to calcuate it-- heck, I’ve probably got a dozen programs that exist solely to do so on old TPUG floppies from 1980. But I’m looking for something I can keep in my head and apply at a moment’s notice.

Or should I just assume everyday was a Wednesday?

[Tripler]

AFAIK, there is no formula that I’m aware of, but there is what’s called a “Perpetual Calendar” I’ve seen in many an almanac. I know, I’m not much help.

I’m sure it’s online somewhere too. . .

Tripler
I will gladly pay you Tuesday for a hamburger today.

[SmackFu]

Here’s one method.

And it’s still not very simple.

[rowrrbazzle]

Here’s one from the sci.math faq at http://www.faqs.org/faqs/sci-math-faq/dayWeek/

1. Take the last two digits of the year.
   2. Divide by 4, discarding any fraction.
   3. Add the day of the month.
   4. Add the month’s key value:

JFM AMJ JAS OND 
144 025 036 146

5. Subtract 1 for January or February of a leap year.
6. For a Gregorian date, add 0 for 1900's, 6 for 2000's, 4 for
   1700's, 2 for 1800's; for other years, add or subtract multiples
   of 400.
7. For a Julian date, add 1 for 1700's, and 1 for every additional
   century you go back.
8. Add the last two digits of the year.
9. Divide by 7 and take the remainder.

Now 1 is Sunday, the first day of the week, 2 is Monday, and so on.