Daily AncestorJulian to Gregorian date converter
Before September 1752, Britain and its American colonies used the Julian calendar with the year starting March 25; add 11 days (10 before March 1700) and fix the year to get today's date.
George Washington was born on February 11, 1731, by the calendar his family used. Today his birthday is given as February 22, 1732. Both are correct. The difference comes from the calendar change Britain and its colonies made in 1752, and it affects every date in colonial records before then.
This converter takes an Old Style date, as written in a colonial record, and gives the New Style date on today's calendar. For dates between January 1 and March 24 it also shows the double-dated form you may see in the record, such as 1731/32.
How to use it
- Enter the day, month, and year exactly as the record gives them. If the record shows a double year like 1731/2, enter the first year. Some writers already started the year on January 1, so for a single-year date from January 1 to March 24, check nearby entries to see how that writer counted.
- Use a date from 1582 to September 2, 1752, the last day of the Old Style calendar in the British colonies.
- Read the New Style date and, when it applies, the double-dated form.
- Record both dates in your notes, marked O.S. and N.S., so the next reader knows which is which.
Worked examples
February 11, 1731 (Old Style)
New Style: February 22, 1732. It may be written February 11, 1731/32.
Eleven days are added. Because February came before March 25, the old year was still 1731, while on today's calendar it was already 1732.
July 4, 1745 (Old Style)
New Style: July 15, 1745.
July falls after March 25, so the year number is the same in both styles. Only the 11 days change.
September 2, 1752 (Old Style)
New Style: September 13, 1752.
This was the last Old Style day. The next morning was printed as Thursday, September 14, 1752, and the eleven days in between were skipped.
Julian vs Gregorian: what changed in 1752
The Julian calendar adds a leap day every fourth year, which is slightly too many. Over the centuries the calendar fell behind the seasons. Most of Catholic Europe switched to the corrected Gregorian calendar in 1582, when the gap was 10 days. Britain and its colonies waited until 1752, and by then the gap had grown to 11 days, because 1700 was a leap year in the Julian calendar but not in the Gregorian.
So in the British colonies, Wednesday, September 2, 1752 was followed by Thursday, September 14. One caution before you convert: a birth that happened before 1752 but was written down years later may already have been changed to New Style by the person recording it. Sometimes O.S. or N.S. tells you which; often nothing does, and a second record of the same event is the best check.
Lady Day and the year that began in March
Under the old English reckoning the year number changed on March 25, Lady Day, not on January 1. A date of February 11, 1731 therefore fell in the same winter that we now call early 1732. The change of year to January 1 took effect in 1752, which is why 1751 was a short year that ran only from March 25 to December 31.
Reading double dates
Clerks knew that people counted the year two ways, so for dates from January 1 to March 24 they often wrote both: February 11, 1731/2. The first number is the legal year of the time, the second the year as we count it now. When you record such a date, keep the double year rather than picking one, and add N.S. when you convert it.
Quaker records add one more twist. Friends numbered their months instead of naming them, and before 1752 March was the first month, so "11th month" in an early Quaker record means January and "12th month" means February.
Questions people ask
What is the difference between Julian and Gregorian calendars?
The Julian calendar has a leap year every four years. The Gregorian calendar skips three leap years every 400 years, which keeps it in step with the seasons. By the 1700s the two were 11 days apart.
When did America switch to the Gregorian calendar?
The British colonies switched in September 1752, when September 2 was followed by September 14. The new year also moved from March 25 to January 1 that year.
What does 1731/32 mean in old records?
It is a double date for January 1 to March 24. The record's year was 1731, because the year then began on March 25; by today's count it was 1732.
What do O.S. and N.S. mean after a date?
O.S. is Old Style, the Julian calendar with the year starting March 25. N.S. is New Style, the Gregorian calendar with the year starting January 1.
How to cite this page
Daily Ancestor. "Julian to Gregorian date converter." Tools. https://dailyancestor.com/tools/julian-gregorian-converter. Last checked 2026-10-15.