James Madison would have been born on March 16, 1751 if he had been born in 1752 instead of 1750. Ralph Ketcham explains:
Because of his birth just before Great Britain's calendar reform in 1752, Madison had two "birthdates," a Julian, or Old Style, one and a Gregorian, or New Style one. A calendar on the wall the night of his birth would have read March 5, 1750, reflecting the eleven-day lag accumulated by the inaccurate Julian calendar, and the designation of March 25 rather than January 1 as the first day of the new year. Adoption of the Gregorian calendar added eleven days to Old Style dates and changed the first of the year date, thus making Madison's birthdate March 16, 1751, New Style, though like many of his contemporaries he sometimes used the Old Style date and/or year in speaking of his birth.