Old Style Dates with Numeric Months


This article discusses how to convert numeric months into the appropriate month name with old style dates.


Changing When the Year Starts

Europe inherited from Roman times a legal year that started on 25 March. Wikipedia has information on how various countries changed over to a legal year starting on 1 January. This article focuses on Britain and British colonies, where prior to 1752, years started on 25 March, with March considered the first month. By law, 1751 was a short year, and 1752 started 1 Jan, with January now the first month. Though the date of changeover may be different in other countries, the principles should be the same.

In years prior to 1752, the year started with March, then April, May, ... December, January and ended with February as shown in the table below. Therefore, when you see month number 1, it was not January as we are used to, but March. Notice that this causes the months with numerically-based names to agree with their number under the old system: September is the 7th month, October the 8th, November the 9th, and December the 10th. The most difficult part of this translation is at the tail end, where month 11 was January and part of the previous year, compared to our modern calendar, and month 12 was February, the last month of the previous year.

Table of Month Numbers

Month Name Old Style Number New Style Number
March 1 3
April 2 4
May 3 5
June 4 6
July 5 7
August 6 8
September 7 9
October 8 10
November 9 11
December 10 12
January 11 1
February 12 2

Interpreting Numeric Months

Just as today, many writers of the time would choose to represent dates with numbers. Anybody that is working in genealogy with dates before 1752 must understand the shift in the beginning of the year so they can properly convert such numeric month designations to the correct month name.

Unless a date is marked by an indication that it is new style (n.s. or N.S., usually), the interpretation of month numbers before 1752 should follow the Old Style column in the above table. That was the standard of the time.


Here are some example dates as they might be recorded prior to 1752, with the appropriate interpretation.

As Written Interpretation Comments
1 of the (3) mo. 1650 1 May 1650 May was the third month
29. 7. 1678 29 Sep 1678 7th month was September
16 : (12) mo : 1649 16 Feb 1649/50 See note below
24o (1o) 1642 24 Mar 1641/42 See note below
18 (12) 1682/3 18 Feb 1682/83 See note below

Notes on Double Dating

Writing old style dates in the period from 1 Jan to 24 Mar can be ambiguous. For a date like 18 Feb 1662, readers will wonder if 1662 refers to the year as used then, or if it has been adjusted to the modern year. (Many writers like to use the modern year numbering, for various reasons. For example, it allows simple comparison and age calculations. See here for one such justification.)

To communicate the exact date precisely without ambiguity, double-dating is used. Thus, the above date becomes either 18 Feb 1661/62 or 18 Feb 1662/63 depending on which of the two interpretations is used. 18 Feb 1661/62 says the date is 18 Feb in the year that was then 1661 but is 1662 in the modern system, while 18 Feb 1662/63 is one year later.

Double dating is not needed for dates 25 Mar or after, since both the old and new styles agree that it belongs to the same year. Sometimes, inappropriate use of double-dating may be a sign of an error. For example 24 Jun 1662/63 could indicate that the month was really January.

Deciding which interpretation was meant can be difficult, but some generalizations are possible.

  • Month 11 or Month 12 are clearly the end of the year just finishing. So "18 (12) 1662" would be 18 Feb 1662/63.
  • Month 1 is clearly the year just beginning. So "18 (1) 1662" would be 18 Mar 1661/62.
  • January or February were almost always part of the previous year. So a contemporary record saying 18 Feb 1662 would be interpreted as 18 Feb 1662/63, unless there is information to the contrary.
  • March before the 25th is ambiguous and is almost impossible to interpret unless one has the context it is seen in, or additional information. In record books, often all of March was included under the heading of the new year. But use of a date in a document may be using the old year since technically it was part of the old year. If a record is taken out of context, you may not be able to determine which is the case. If there is not enough information to make an educated guess, it is better to avoid double-dating, rather than guess. Leave it for somebody else to supply the missing information needed to select which of the two possible interpretations is correct.

Notes on Source Citations

In date fields, WeRelate guidelines suggest dates be put in the form DD MMM YYYY with 3-letter month abbreviation. Using all numeric dates is explicitly discouraged. For numeric dates, the user is expected to make the appropriate translation to the correct month name.

When a source gives a numeric date, the source citation should preserve that format so that future readers may see both the original as well as the interpreted form.

For example, the text of a source citation of a genealogy book might say the following:

John Doe was born "10 (1) 83" [10 Mar 1682/83].