Until 1752, Britain and her colonies were still using the Julian calendar. Under this system, March 25 was considered the first day of the new year. Benjamin Franklin’s birth date was then recorded as January 6, 1705, and George Washington’s February 11, 1731 (Old Style).
When the calendar was changed to reflect the Georgian system, which is the one we still use, dates were altered by eleven days, making Franklin’s birthday, as we know it, January 17, 1706 and Washington’s February 22, 1732.
(Isaacson 15ff)