Happy New Year! Double Dating Explained

Happy New Year
A vintage advertisement for
Londonderry Lithia Springs Water
from the Prohibition Era

This is an update of a blog post originally written in 2010, and revised in 2015, and now re-edited and updated for 2020!

Double dating for historians and genealogist is not the same double dating you did in high school when you didn't have partner for the homecoming dance.  This is the double dating that confuses you in history books and vital records.  If you use a genealogy data base like Ancestry or Family Tree Maker, your software may actually change or challenge any dates you enter pre-1752 between January and March 24.  Or you may have tried to figure out how to calculate a date during this time period, only to notice that you were off by three months somehow when you finally find the correct vital records.  What is going on here?

The date 10/21 February 1750/51 is an example of double dating.  It appears to have too many numbers, or it appears to be a guess to some readers, such as an approximate date. However, this is a real date on the calendar, along with an interesting story...

In 1752 there was a calendar change between the Julian and Gregorian calendar systems.  The Julian calendar had been invented during Roman times, and on the advice of his astronomer Julius Caesar started this new system in 45 B. C.  It is officially known as the Old Style calendar.  You might even see a date with the notation "O. S.".  Under this calendar, New Year's Day was on March 25th, and the last day of the year was March 24.  The new Gregorian calendar established January 1st as the first day of the new year.

Why?  Because sometime during the medieval period, the astronomers noticed that the calendar year was not accurately measuring the solar year.  In 1582 Pope Gregory XII reformed the calendar, which is now called the New Style Calendar or Gregorian.  It was first adopted in catholic countries, and later in the Protestant countries.  In order to make the adjustment, ten days were removed, so that 4 October 1582 was followed by 15 October 1582.  England and other Protestant countries did not adopt the New Style until 1752, and then they removed eleven days from the calendar again, so on 2 September 1752 the next day was 14 September 1752.

And so we see double dating used in Colonial America for the dates between 1 January and 24 March on the years between 1582 and 1752.  This was common in old records, especially in civil records.  Some church records continued to use the old system, especially the Quakers who used "First Month" for March, "2nd Month" for April, "3rd Month" for May to avoid using the names of the Roman Gods - January for the god Janus or August for Augustus, which were pagan names.  The Quaker record 3/12/1719 became 12 May 1719.  Some Puritan communities in New England used this system, too.

If a date was recorded in a civil or church record with double dating, it is correct to leave it as such, and to try to recalculate the date for your records.  Check to see which style was used in the original primary source record.  The date should be written just as you find it, for example 20 January 1745 OS (if it was Old Style) or as 20 January 1745/6.  If an explanation is needed, put the explanation in the notes, footnote or endnote.

"Most people find dates repulsive enough without encountering them disguised as fractions" by historian Garrett Mattingly, from his book The Defeat of the Spanish Armada in which he opted to just use the Gregorian dates (Wikipedia).

For more information:

Marking Time: The Epic Quest to Invent the Perfect Calendar, by Duncan Steel, J. Wiley Publisher, 2000

"Double Dating" from Vita Brevis, the NEHGS blog   https://vitabrevis.americanancestors.org/2015/01/double-dating/ 

The 2015 version of this blog post:
https://nutfieldgenealogy.blogspot.com/2015/12/happy-new-year-from-nutfield-genealogy.html 

An example of a Connecticut tombstone with double dating:
https://nutfieldgenealogy.blogspot.com/2016/06/tombstone-tuesday-sarah-treat-goodrich.html 

and a Massachusetts tombstone with double dating:
https://nutfieldgenealogy.blogspot.com/2016/12/tombstone-tuesday-joseph-herrick-buried.html

This New Hampshire tombstone should have used double dating to explain a conundrum:
https://nutfieldgenealogy.blogspot.com/2014/02/tombstone-tuesday-grandmother-and.html 

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To cite/link to this blog post: Heather Wilkinson Rojo, "Happy New Year!  Double Dating Explained", Nutfield Genealogy, posted January 1, 2019, ( https://nutfieldgenealogy.blogspot.com/2020/01/happy-new-year-double-dating-explained.html: accessed [access date]).