The English year didn’t change until March 25, or Lady Day, when Christians celebrate the Feast of the Annunciation of the Blessed Virgin. So in 1620, John Winthrop's father Adam wrote in his diary, "The new year beginneth," on March 25.
The whole thing started with Julius Caesar. In 45 B.C., he ordered a new calendar, one with 12 months, 365 days and a start date of January 1. Every fourth year would include a leap year to compensate for the extra six hours or so it takes the earth to revolve around the sun.
By the 9th century, some southern European countries began celebrating the first day of the year on March 25 to coincide with the Annunciation. Balky England didn’t follow along until the 12th century.
By the 16th century it became obvious that the Julian calendar overcompensated with too many leap years. Equinoxes were falling 10 days too early. Catholics were concerned Easter wasn’t celebrated in the proper season. So in 1582, Pope Gregory XIII approved the New Style, or Gregorian calendar. Ten days were dropped from October 1582 and leap years came slightly less often. Only millennia years divisible by 400 would have leap years. January 1 would be New Year’s Day.
Most of Europe went along with the change. England did not. In 1582, Protestant Queen Elizabeth I was not inclined to take orders from the Catholic Church. March 25 remained the legal start of the new year. But the English people began celebrating January 1 as New Year’s Day along with the rest of Europe. Almanac publishers went along with them, too.
That’s how double dating got started in colonial record keeping. Dates between Jan. 1 and March 25 were identified with a slash mark between the years that overlapped. Just as an example, records of the first parish in Brewster, Mass., show double dates: ’Eleazer Crosbeys Eunice baptized on Jan : 9 . 1731/2’ and ‘Jonathan Cobb admitted on March 19 . 1731/2.’
Double dating wasn’t for everyone, as the Connecticut State Library points out. The Colony of Connecticut’s records show a court at Hartford on 27 December 1636 followed by a court at Hartford on 21 February 1636 followed in turn by a court at Hartford on 28 March 1637. You might think the February session was recorded out of sequence, but it’s correct: December 1636 was followed by January and February 1636, and 1636 continued until March 24.
England and her colonies finally caved in to the new calendar when Parliament passed the Calendar Act of 1750. As of 1752, January 1 was officially the new year and 11 days were dropped from September.
Historians generally list both Old Style and New Style dates for pre-1752 records. Look up Ethan Allen, for example, and you’ll see his dates listed as ‘January 21, 1738 [O.S. January 10, 1737] - February 12, 1789.’ But that isn’t always the case. George Washington changed his birthdate from Feb. 11, 1732 under the Julian calendar to Feb. 22, 1732 under the Gregorian calendar.
So a word to the wise historian: Be careful how you date!
This story was updated from the 2013 version.