# Formula for determining the day of a given date?

**URL:** <https://boards.straightdope.com/t/formula-for-determining-the-day-of-a-given-date/219443>\
**Category:** Factual Questions\
**Created:** [December 17, 2003, 2:12am UTC](https://boards.straightdope.com/t/formula-for-determining-the-day-of-a-given-date/219443 "2003-12-17T02:12:44Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Boogers](https://avatars.discourse-cdn.com/v4/letter/b/d2c977/32.png) [@Boogers](https://boards.straightdope.com/u/Boogers)\
**Post date:** [December 17, 2003, 2:12am UTC](https://boards.straightdope.com/t/formula-for-determining-the-day-of-a-given-date/219443/1 "2003-12-17T02:12:44Z")

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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?

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**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\
**Post date:** [December 17, 2003, 2:15am UTC](https://boards.straightdope.com/t/formula-for-determining-the-day-of-a-given-date/219443/2 "2003-12-17T02:15:56Z")

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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.

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**Author:** ![SmackFu](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@SmackFu](https://boards.straightdope.com/u/SmackFu)\
**Post date:** [December 17, 2003, 2:32am UTC](https://boards.straightdope.com/t/formula-for-determining-the-day-of-a-given-date/219443/3 "2003-12-17T02:32:51Z")

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[Here’s one method.](http://quasar.as.utexas.edu/BillInfo/doomsday.html)

And it’s still not very simple.

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**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\
**Post date:** [December 17, 2003, 3:02am UTC](https://boards.straightdope.com/t/formula-for-determining-the-day-of-a-given-date/219443/4 "2003-12-17T03:02:42Z")

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Here’s one from the sci.math faq at [http://www.faqs.org/faqs/sci-math-faq/dayWeek/](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:
> 
> ```auto
> 
> 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.