RJ's answer is, of course, correct, but in case someone reading this needs the broader context, here it goes: Apologies if I am rehashing something you already know, but there is no "Quaker calendar" per se. The Quakers changed from the Julian to the Gregorian calendar at the same time as everyone else in the English-speaking world, as explained by RJ above. What makes Quaker dates especially confusing is that they referred to the months numerically ( 1st month, 2nd month, etc) rather than by their "Pagan" names (January, February, etc.). Thus, under the Julian Calendar, first month meant March, and twelfth month was February. Thus, the Quaker usage has led to a lot of confusion -- e.g., until 1752, "8th month" was October, not August. At least, with the "pagan" months, you know August means August, regardless of the year. Consequently, if you see a Quaker birth date reported as "August 11, 1732" by some secondary sources, and "October 11, 1732" by others, it's a fairly good bet that the October date is the correct one, but you really need to see the primary source to be sure. January and February (11th and 12th month, old style) need special attention due to the change of year. To convert 11th or 12th month (i.e., January or February) under the old calendar, you would need to add a year -- i.e., 11th month (January) 1731 under the Julian calendar would be 1st month (January), 1732 under the Gregorian Calendar. Consequently, people will often write "January (or February), 1731-2" just to be sure there is no doubt. For all the months other than January and February, the year would not need to be changed. It's a helpful practice to specify which calendar you are using for dates before the change-over in 1752.
