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What's Benjamin Franklin's Birthday?Why it's 11 days later than it used to be.

By Daniel Engber
Updated Wednesday, Jan. 18, 2006, at 5:52 PM ET

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On Tuesday, Jan. 17, the city of Philadelphia celebrated Benjamin Franklin's 300th birthday. According to the Boston Globe, Franklin was actually born on Jan. 6, 1706, but that was before the colonies switched from the Julian to the Gregorian calendar. When Great Britain updated to the new system by skipping 11 days in 1752, Franklin dutifully moved his birthday. Did everyone change birthdays in 1752?

No. Most people were happy to keep their original dates. The Gregorian calendar had been in effect for most of Europe since the 16th century, when Pope Gregory XIII issued a papal bull that established the new system. Not everyone went for the idea right away, and Great Britain held out for 170 years. (The Church of England was particularly resistant to the proposal from Rome.) Some people protested when Parliament finally made the change. Posters were drawn up saying ,"Give us back our eleven days."

Franklin supported the change from the start. "Be not astonished," he wrote in his Almanack, "nor look with scorn, dear reader, at such a deduction of days, nor regret as for the loss of so much time …" Other prominent Americans supported the new system; George Washington updated his own birthday from the old Feb. 11 to the Gregorian Feb. 22. Even so, the majority of early Americans held on to the birthdays they'd always used.

The calendar switch of 1752 included another significant change. Under the Julian system, the year began on March 25. That means a colonist who went to bed on March 24, 1700, would wake up on March 25, 1701. The new Gregorian rules set the start of the year to Jan. 1.

This created some confusion, since anyone who was born between Jan. 1 and March 25 in the old system would have the wrong birth year in the new one. George Washington's old-style birthday was, in fact, Feb. 11, 1731. Genealogists and some record-keepers of the time used a system called "double dating" for cases like these: Washington's date of birth might have been recorded as 1731/1732. (Today we consider him to have been born in 1732.)

The same logic should apply to Franklin, since he was born in January. But the Globe puts his old-style birthday in 1706—wouldn't that make his Gregorian year of birth 1707, and the celebrations in Philadelphia a year early?

Franklin created some of this confusion himself with a faulty reference in his autobiography. Speaking of his uncle, Franklin writes: "He died in 1702, the 6th of January, four years, to a day, before I was born." That suggests he was born on Jan. 6, 1706, an old-style date that translates to the Gregorian Jan. 17, 1707. But according to documents from Boston's city registrar, he actually came into the world on the old-style Jan. 6, 1705. So, this year's tricentennial is right on time.

Got a question about today's news? Ask the Explainer.

Explainer thanks Leland Meitzler of Heritage Creations and Kory Meyerink of ProGenealogists, Inc.

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Daniel Engber is an associate editor at Slate. He can be reached at .
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