Old Style ↔ New Style Date Converter

What does Old Style/New Style mean?

Old Style (OS) refers to the way the year was numbered when the legal new year began on March 25th (Lady Day) rather than January 1st. Dates recorded between January 1st and March 24th therefore carried the previous year’s number.

For example, an English record dated “10 February 1700” was recorded as 1700 under the Old Style system but falls in 1701 under the New Style year.

What is a dual date?

Record-keepers sometimes wrote both year numbers to make the difference clear. A date such as “10 February 1699/1700” means the date was 1699 according to the Old Style legal year but 1700 according to the New Style year.

A dual date is not a range or an uncertain date. It records both year reckonings. When transcribing a historical record, retaining both numbers preserves information that can otherwise be lost.

When did different countries adopt the Gregorian calendar?

Adoption occurred at different times by country and territory. Some major examples:

Catholic Europe: many countries adopted the Gregorian calendar in 1582, when Thursday, October 4th (Julian) was followed by Friday, October 15th (Gregorian).

Scotland: changed the legal new year to January 1st in 1600 but retained the Julian calendar until 1752.

England and Wales: 1752, changing both the calendar and the start of the legal year.

Russia: 1918.

Greece: 1923.

Adoption dates varied among individual states and territories, particularly in the German and Eastern European regions, and the calendar change and the change to a January 1st new year did not always happen at the same time. The place and date of the record should be considered before converting it.

Why does the calculator change only the year?

Two different things changed in England and Wales in September 1752, at the same moment: the calendar, which moved the day by eleven days, and the start of the legal year, which moved from March 25th to January 1st. Because they happened together, they are often treated as one change. They are not. Old Style ↔ New Style corrects only the year number; the calendar difference is a separate correction.

Which corrections a record needs depends on where and when it was written, and on the time of year. An English record from June 1740 is Julian, so the day needs correcting, but the year does not — June falls after March 25th. An English record from February 1740 needs both: the year, because February fell before the legal new year, and the day, because the calendar was still Julian. A Scottish record from February 1700 needs the day corrected but not the year, since Scotland had moved its new year to January 1st in 1600 while keeping the Julian calendar. A French record from the same February needs neither.

This calculator handles the year. For the day, use the Julian ↔ Gregorian converter.

Why do some records have numbered months?

Some record-keepers, particularly Quakers, used numbers instead of month names. Before 1752, when March was the first month of the legal year, the 7th month was September. After the change to a January-based year, the numbered months shifted, so the date of the record determines how the number should be interpreted.

This is separate from abbreviations such as 7ber, 8ber, 9ber, and Xber. Those abbreviations come from the Latin month names and mean September, October, November, and December regardless of the calendar or year numbering.

Why did the new year move to January 1st?

It was less a move than a return. January 1st had been the start of the Roman civil year since Julius Caesar’s calendar reform, and the Julian calendar England used had always counted its months from January. March 25th — Lady Day, the feast of the Annunciation — was a medieval church convention adopted for the legal year in England around the twelfth century, and it never displaced January 1st entirely: almanacs and everyday reckoning often ran from January, which is why record-keepers wrote dual dates for the months in between.

Most of Europe had settled on January 1st by the sixteenth century, Scotland in 1600. When England and Wales reformed the calendar in 1752 they took the opportunity to bring the legal year into line with the calendar year everyone else was already using.

Should I record the converted date or the date in the record?

Standard practice is to record a date exactly as the source gives it and note the calendar or year system — “3 March 1700 (Julian)”, “10 February 1700 (OS)” — rather than replace it with the converted equivalent. The original form is what a later researcher will find when checking the same register, and a converted date with no note can be mistaken for a transcription error.

Conversion is for comparison. When dates from records using different calendars need to be compared, bringing them onto a single calendar makes the difference between them clear. The converted date can be recorded alongside the original, but it should not replace it without explanation.

What is the difference between a Julian date and an Old Style date?

Julian refers to the calendar itself; Old Style refers to the way the year was numbered before the legal new year moved to January 1st. They are related, but they describe different things.

Julian ↔ Gregorian moves the day: the difference is ten to thirteen days, depending on the century. Use it when a record was written while the Julian calendar was in force and the date needs to be compared with a Gregorian one.

Old Style ↔ New Style moves the year: use it when a pre-1752 English or Welsh record falls between January 1st and March 24th and the question is which year it belongs to.

A date can need both. “5 February 1740/41” in an English register needs the year settled first and the day correction second.