How to Find the Day of the Week

May 6, 2009
Antique Pocketwatch

It’s easy to find out the day of the week for births, weddings, and other historical events. Follow our instructions to calculate the day for any date in history—as far back as the mid-1700s.

For example, what day of the week was December 26, 2004, when the tsunami struck in the Indian Ocean? Follow the example as you read along:

  1. Take the last two digits of the year.
  2. Add to that one–quarter of those two digits (discard any remainder).
  3. Add to that the day of the month and the Month Key number for that month:

     

    January = 1 June = 5
    …leap year = 0 July = 0
    February = 4 August = 3
    …leap year = 3 September = 6
    March = 4 October = 1
    April = 0 November = 4
    May = 2 December = 6

     

  4. Divide the sum by 7. The remainder is the day of the week! One is Sunday, two is Monday, and so on. If there is no remainder, the day is Saturday.

Note: 

  • If you’re searching for a week prior to 1900, add 2 to the sum before dividing; prior to 1800, add 4.
  • The formula doesn’t work for days prior to 1753.
  • From 2000 to 2099, subtract 1 from the sum before dividing.

Here’s an Example:

A tsunami occurred in the Indian Ocean on December 26, 2004.

Last two digits of year 04
One-quarter of these two digits 1
Given day of month: 26
Key number for December 6

Sum: 37

Because 2004 is in the range of 2000 to 2099, subtract 1 from 37. This yields 36.

36 divided by 7 = 5, with a remainder of 1. The tsunami took place on Sunday, the first day of the week.

Monday’s child is fair of face,
Tuesday’s child is full of grace,
Wednesday’s child is full of woe,
Thursday’s child has far to go,
Friday’s child is loving and giving,
Saturday’s child works hard for a living,
And the child that is born on the Sabbath Day,
Is bonny and blithe and good and gay.

–an old English nursery rhyme

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Reader Comments

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Small Correction

The first note is incorrect, It should read:

If you’re searching for a week prior to 1900, add 2.
If you’re searching for a week prior to 1800, add 4.

Instructions revised

The Editors's picture

Hi, Bob,
We have corrected the error and revised the copy a bit. Thank you for the heads up!

can't make your formula work

can't make your formula work