Old Style vs. New Style years
Updated February 23, 2017 | Factmonster Staff 
The Question:
Your 2/11/1731 O.S. date of birth for George Washington is off by one year. It should be 2/11/1732 O.S.
The Answer:
Our encyclopedia entry for George Washington gives his birthday as Feb. 22, 1732 in our current calendar, and Feb. 11, 1731, Old Style. At first glance, this seems absurd; while the Julian calendar that used to be used wandered off course over the centuries, the difference amounted to eleven days at that point, not a year and eleven days.
There's one more detail, however: under the calendar in use when Washington was born, the year began on March 25, not January 1. As a result, February 11, 1731 O.S. is, in fact, February 22, 1732 in our current system.
-The Fact Monster
