How often is Leap Day on Friday?

February 29, 2008 | By | Reply More

Today is/was Leap Day, or that extra day wedged into the Intercalary Year to fudge for God not having created a year with a whole number of days to help keep things straight. I received an email from a friend asking how often does Leap Day come on a Friday? I’m used to fielding odd math questions.

Anyway, the answer is every 28 years, ignoring century years not divisible by 400. I first got that by running the year cursor forward on the Windows clock setting window. Then I worked out why this is.

Look at any 4 year period. It has exactly 1,461 days, or 208 weeks plus 5 days. Again, unless it crosses a non-leap century year (like 2100). So every leap year the day of the week moves back by 5 days. How many 5/7 ths does it take to get back to a whole number? Yep, seven. So 4 year periods by 7 cycles is 28 years.

What about Sadie Hawkin’s Day? November 19th, and has been since Al Capp invented it in 1937. But Leap Day is the date on which it is traditionally acceptable (in English tradition) for a woman to propose to a man. Thus the confusion.

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Category: American Culture, History, Whimsy

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A convoluted mind behind a curly face. A regular traveler, a science buff, and first generation American. Graying of hair, yet still verdant of mind. Lives in South St. Louis City. See his personal website for (too much) more.

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