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Doomsday Calculator

Using the doomsday algorithm, this calculator enables you to learn how to calculate the weekday of any given date without the help of calculators, computers, or calendars.

Enter the date to calculate

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This result is based on the Gregorian calendar and might differ from the actual weekday in some countries.

1) How many times does the number 12 fit as a whole into the two last digits of the year number?

Last two year digits: 25

12 fits in 2 time(s)

2) What is the difference between the two last digits of the year number and the product of the multiples of 12 from calculation 1 (remainder)?

Last two year digits: 25

12 times Step 1: 12 x 2 = 24

25 - 24 = 1

3) How many times does the number 4 fit into the result of calculation 2?

Result from last step:1

4 fits in : 0 time(s)

4) What is the century's anchor day?

  • 1900-1999 - Wednesday (3)
  • 2000-2099 - Tuesday (2)
  • 2100-2199 - Sunday (0)
  • 2200-2299 - Friday (5)

5) Add up all the results.

2 + 1 + 0 + 2 = 5

6) Subtract whole multiples of 7 from the result of calculation 5.

This will result in a number between 0 and 6, which corresponds to the doomsday of the year.

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

7) Find the closest doomsday.

  • January 3
  • February 28
  • April 4
  • May 9
  • June 6
  • July 11
  • August 8
  • September 5
  • October 10
  • November 7
  • December 12

8) Count forward/backward from the doomsday to the specified date.

  • 04 April 2025 Friday
  • 11 April 2025 Friday
  • 12 April 2025 Saturday
  • 13 April 2025 Sunday

Example Uses

Calculate the day of the week for:

  • your birthday
  • next Christmas
  • a historical event, like the first Moon landing