Old Style to New Style.

Worked example

George Washington’s birth is recorded as 11 February 1731 O.S. Because the British legal year began on 25 March, that date is in 1731 by the old count but belongs to 1732 by modern year numbering, written 1731/32. The Julian and Gregorian calendars were 11 days apart then, so the converter gives 22 February 1732, the date now officially reported. Another check is the 1752 change itself: Wednesday 2 September 1752 (O.S.) was followed by Thursday 14 September 1752 (N.S.), so 3 September O.S. converts to 14 September.

How it works

The Julian calendar adds a leap day every four years and the Gregorian calendar skips it in century years not divisible by 400, so the two drift apart. The gap was 10 days when the Gregorian calendar began, 11 days when Britain adopted it in 1752 (because 1700 was a leap year in the Julian calendar only), 12 days in the 1800s and 13 days from 1900 until 2100. The tool converts through the Julian Day Number, so the gap is exact for any date.

Old Style and New Style (O.S. and N.S.) refer to the dating systems before and after a calendar change. In England, Wales, Ireland and Britain’s American colonies there were two changes in 1752: the start of the year moved from 25 March to 1 January, and 11 days were dropped to match the Gregorian calendar. Scotland had already moved its year start to 1 January in 1600. Dates from 1 January to 24 March in the old system were often written with two years, such as 1731/32. Other countries changed at other times; Russia, for example, made the Gregorian calendar its civil calendar in 1918.

Sources and basis (opened 2026-10-08): Old Style and New Style dates - Wikipedia (1752 changes, 25 March year start until 1752, Scotland 1600, Washington example, 2 September to 14 September 1752, 13 days until March 2100, Russia 1918).

FAQ

What do O.S. and N.S. mean in dates?

Old Style (O.S.) and New Style (N.S.) indicate dating systems before and after a calendar change. Usually they mean the Julian calendar and the Gregorian calendar.

When did Britain switch to the Gregorian calendar?

In 1752. Wednesday 2 September 1752 was followed by Thursday 14 September 1752, which dropped 11 days. The start of the year also moved from 25 March to 1 January that year.

What does a date like 11 February 1731/32 mean?

It is a double date. In England the legal year began on 25 March, but many people already treated 1 January as the new year, so dates from 1 January to 24 March were written with both years. By modern numbering it is February 1732.

How many days apart are the Julian and Gregorian calendars?

The gap grew from 10 days when the Gregorian calendar began to 11 days in the 1700s, 12 days in the 1800s and 13 days from 1900 until March 2100. This tool works the exact figure out for each date.

Did Scotland also start the year on 25 March?

No. Scotland moved the start of its year to 1 January in 1600, so choose the 1 January option for Scottish records from 1600 onward.

Can I use this for Russian or Orthodox dates?

It converts between the two calendars for any place, so it works for Julian-dated records. Choose the 1 January option. Russia made the Gregorian calendar its civil calendar in 1918.