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Today is Doomsday!

February 29, 2016

Today, the last day of February, is a special day that lets you determine, in your head, the day of the week for any date this year.

This year, the last day of February falls on a Monday, and that's what you need to remember -- in 2016, it's a Monday.

Okay, here we go... For the even-numbered months after February, the Nth day of the Nth month is a Monday.

So Apr (4th month) 4th is a Monday, June (6th Month) 6th is a Monday, and Aug 8th, Oct 10th, and Dec 12th are all Mondays.

Example: What day of the week is Christmas this year? Dec 12th is a Monday, so is the 26th, so Christmas is a Sunday this year.

For the odd-numbered months, remember this mnemonic phrase -- "I work from 9 to 5 at the 7-11."

The mnemonic works like this -- Sept (9th month) 5th is a Monday, and May (5th month) 9th is a Monday.

Example: When is May Day this year? Since May 9th is a Monday, so is May 2nd, so May Day is on a Sunday this year.

Similarly, July (7th month) 11th is a Monday, and November (11th month) 7th is a Monday.

Example: What day of the week is Canada Day this year? July 11th is a Monday, so is the 4th, so Canada Day is a Friday this year.

March is easy since the 7th of March is always the same day as the last day of February.

Example: When is St. Patrick's Day this year? March 7th is a Monday, so is the 14th, so St. Patrick's Day is a Thursday this year.

Finally, it's January 3rd for 3 years, and January 4th every 4th year, leap year.

Example: When was New Year's Day this year? January 4th was a Monday, so January 1st was a Friday this year.

This algorithm was created by John Horton Conway, and is explained in detail on my web page, Doomsday Algorithm

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