Charles I death warrant
The Death Warrant of King Charles I,

Millions of British citizens and their colonial counterparts across the Atlantic Ocean went to sleep on 2 September 1752 and woke up on 14 September. This shift in dates was due to an Act of Parliament passed in 1750, known as Chesterfield’s Act, which put into motion a series of changes that fundamentally altered the way that many measured time.

The calendar used by many nations around the world (including both Britain and America) was originally created by Julius Caesar in the year 45 B.C.[1] This calendar employed a system of 365 days spread out into 12 months with every fourth year having 366 days (a leap year). This calendar moved the first day of the year to January 1st from its original date of March 1st. However, when the Roman Empire fell in the 5th century, the calendar was once again realigned to coincide with Christian Festivals. By the 9th Century, some countries began celebrating the first day of the New Year on March 25 to coincide with Annunciation Day (the church holiday nine months prior to Christmas celebrating the Angel Gabriel’s revelation to the Virgin Mary that she was to be the mother of the Messiah).[2]

In 1582, Pope Gregory XIII introduced and recommended use of the Gregorian Calendar, which dropped ten days from October 1582 to correct issues regarding the dates of equinoxes and seasonal changes and re-established 1 January as the beginning of the calendar year.[3] However, several countries that rejected the authority of the Pope, including Britain, did not adopt the Gregorian Calendar, instead retaining the “Old Style” Julian Calendar.[4]

This discrepancy in dating systems led to a unique situation familiar to many genealogists. Given the differences in how certain governing bodies and independent citizens represented the date, a system known as dual or double dating was frequently applied.[5] In this system, the year was written using two consecutive digits at the end, separated by a ‘/’ or ‘–‘ (for example, 1727/28), as a means of representing the current date utilizing both dating systems. (This form was used for the disputed months between January and March; dates falling outside these months are regarded as belonging within their calendar year.) Dual dating was common on both formal and informal documents in many European countries and their colonies for centuries. The American colonies applied double dating to documents until 1752.[6]

In 1750, the British Parliament passed the Calendar (New Style) Act. The Act stated “The old supputation of the year not to be made use of after Dec. 1751. Year to commence for the future on 1 Jan. The days to be numbered as now until 2d Sept. 1752; and the day following to be accounted 14 Sept. omitting 11 days.”[7] Therefore, 1 January became the first day of the year 1752.  Also, as noted in the introduction to this article, 2 September 1752 was followed by 14 September 1752, thus removing the eleven day difference created by the shift in dating systems.

Thomas Jefferson monument
Gravestone of Thomas Jefferson, courtesy of Find A Grave,

The dual dating system is often found by historians and genealogists in a variety of official documents, personal correspondence, and at times, in more permanent locations. The usage of the Julian Calendar prior to 1752 is a fact that historians must be aware of when conducting research, one example being the death warrant for King Charles I of England. During his reign, the High Court of Justice in England issued a warrant declaring Charles I guilty of many crimes, chief among them being treason. The document is dated 29 January 1648.  However, since the new year began on 25 March according to the system utilized by the English at this time, this event would have taken place in the year 1649 based upon the modern calendar.[8]

While the Calendar (New Style) Act of 1750 effectively ended the use of double dating in the American colonies, the legacy of the dating system survived much longer. In the graveyard of the Monticello, the gravestone of Thomas Jefferson, third President of the United States, notes that his date of birth was “2 April 1743 O.S.” (Old Style), as Jefferson was born prior to the 1750 Act of Parliament.[9] The final nations to adopt the Gregorian calendar were Greece (1923) and the Soviet Union (1929).[10]


[1] ‘sclapp,’ “The 1752 Calendar Change” Connecticut State Library, 2011,

[2] Ibid.

[3] Wells, D. W. and R. F. Wells. 1910. A History of Hatfield Massachusetts,

[4] ‘sclapp,’ “The 1752 Calendar Change” Connecticut State Library, 2011,

[5] Spathaky, Mike, “Old Style and New Style Dates and the Change to the Gregorian Calendar: A Summary for Genealogists,” GENUKI,

[6] ‘sclapp,’ “The 1752 Calendar Change” Connecticut State Library, 2011,

[7] UK Legislation, Calendar (New Style) Act 1750, 1750 c. 23 (Regnal. 24_Geo_2),

[8] “Death warrant of Charles I: HLRO Main Papers (1660)” UK National Archives,

[9] Gravestone for Thomas Jefferson, Monticello Graveyard, Albemarle County, Virginia, Find A Grave Memorial #: 544, maintained by: Find A Grave.

[10] Heper, Metin, ed. The Routledge Handbook of Modern Turkey (Routledge, 2013), p. 54.

About Zachary Garceau

Zachary Garceau joined the Research and Library Services team in 2014 after receiving a master’s degree in Historical Studies with a concentration in Public History from the University of Maryland-Baltimore County and a B.A. in History from the University of Rhode Island. Zack also works for the Rhode Island Department of Health as the Chief of the Office of Health Regulation. Areas of expertise: Rhode Island, French-Canadian Genealogy and Sports History. He also enjoys working on heraldic and royal research.

15 thoughts on “Double-dating

  1. Once again I enjoyed your article. Your subjects are so interesting and also you have a unique flare of entertainment. Thank you Lorraine McLaughlin

    1. As usual thus article was immensely interesting, who knew! Learning history with vita-brevis has me waiting anxiously for the next article.

      Thank you so much


  2. Zack – Ann and Lorraine are entirely correct. Your articles are ever so informative, well done, and entertaining. Please do keep them coming. – Good work and many thanks!

    J. Record

  3. Next UP — “7 mo. 4d. 44” means ??? (Just a suggestion if you are doing dating reminders. Then, too, there are Regnal Years.)

    1. As no one has picked up on the potential confusion of this date recording method, I need to clarify why I posed the challenge and provide the answer.

      “7 mo. 4d. 44”, as a record in English created during the 17th century, could be interpreted as 4 July 1644. That is incorrect. For the English, the 1st month was March and all of March, even though the actual New Year’s Day in that system was Michaelmas Day, the 25th. So 7th = SEPtember. Thus 8th = OCTober, 9th = NOVember and 10th = DECember.

      If the date recorded was “12 mo. 11d 44”, it means in our present system that the date was 11 February. But, aware of the date-split problem, does “44” really mean 1643, 1644, or 1645?

      Here, you have to ask yourself, what is the context of the date? Usually, someone using this system means the year we would call 1645. We would then present it genealogically as “11 February 1644/5”.

      But what if the year dates just before and after it in a record were 11 November 1643 and 4 September 1645? Then we should present it as “11 February 1644[/5?]”. Because we just don’t know for certain if it was our “1643/4” or “1644/5”, and so we are OBLIGED to our fellow researchers in years to come to directly state our uncertainty.

      I would present the above as “so-and-so” d. Weymouth “12 mo. 11d. 44” (11 February 1644[/5?]).

  4. Very interesting; I first learned about Old Style and New Style while researching my Plymouth Colony ancestors. Another curious dating nomenclature was that of the Society of Friends. They would say third day, fourth month (instead of 3 March, I think) because the day and month names were derived from the mythological gods (e.g. Thursday meaning the day of Thor).

    1. Or is that 3 June, eh? Sitting here, I don’t remember if Quakers used Jan or March as 1st month from their origins or when they shifted, if they did, before 1752.

  5. So could someone please make a document aligning the old dates to dates of our time so if I find a birth date of John Alden as _____________in Mayflower Families, is that the old calendar or the modern calendar? I f, old and I had a chart I could then check equivalency. I am not a chart designer but i sure could use one and I hope we have some guidance on how to cite dates as we wrrite articles-should we announce it at beginning or article?
    Mary Maher Boehnlein, Ph.D.

    1. See Zach’s note about Tom Jefferson’s gravestone above. TJ “kept” his original birth date because that was the actual date then. However, George Washington chose to celebrate his “adjusted” birth date February 22. TJ kept to “O.S.” – Old Style, while GW went “N.S.” – New Style. That was an individual style choice. However, no original records were changed.

      The convention in history writing was to note, somewhere in the front matter or at least in the back matter if that’s where the footnotes appear, that all dates before 2 September 1752 are Old Style, while all subsequent dates from 14 September are New Style. That is, you the writer haven’t changed the dates as they appear in the document.

      Thus, the date of the Mayflower Compact is what appears on the document itself,11 November 1620, and not 22 November 1620, and no one bothers to write it as “11 November 1620, O.S.” or as “22 November 1620 N.S.” Such a pro forma disclaimer appears in the foreword to my master’s thesis on Maine settlement and land development (1632-1815), for instance, because that was then .

      This convention is so well known that it is now PRESUMED that that’s the case, unless you specifically state otherwise. As you might, if you need to match up a papal document’s date (post-October 1582) with a response to it from the English government as part of an analysis, or if you the writer are switching back and forth from events happening in England to events happening in Spain and France, as Garret Mattingly does so well in The Armada (1959). He states his O.S. / N.S. position in his foreword, but gives a few reminders at places in his text where some timing issues are important.

      That presumption carries over to genealogy too. When quoting / citing from original records, you do not change anything. You may have to explain why an original date / fact may be incorrect, but you do not silently change it. Thus, Deacon Robert Cushman, originally on the Mayflower, was indeed baptized at Rolveden, Kent on 9 February 1577/8. And as that’s true, there’s no point in changing it to 20 February 1578 N.S.

      Just too many dates!

  6. At the risk off sounding too post modern, I agree with Mary Mayer Boehnlein – a simple (?) reference chart would be nice (no doubt perhaps one exists already) or, a software program where modern dates might be ‘translated’ forwards and backwards to and from the various styles of chronology and of time’s keeping.

    While I agree with Robert M. Gerrity that much of the dating is definitely “presumed,” it would be excellent to have a handy ‘ap’ when one’s brain isn’t working in an algorithmic mode, and perhaps supply we novitiates with a way to at least strive towards historical accuracy rather than just supplementing it.

    A good subject never in want of discussion!

    Best regards,

    J. Record

    1. The genealogy database program I use, Roots Magic, automatically compensates for the “missing 11 days” in its calendar function for dates in “English”, which is an APPLICATION within the overall program. Your database likely does the same. These programs now have I-Phone and Droid versions that you can put on your phone.

      Now by compensate I mean that if you only had a person’s death date and then his age at death expressed in years, months and days, the program would calculate a birth date that should give you his actual recorded birth date. Thus the app will calculate Washington’s birth day as the RECORDED date, 11 February, not 22 February. By convention, just because GW made the personal choice to do so, the 22nd is now the “official date” and we do not bother to make the Old Style and New Style differentiation –UNLESS, as at the Wikipedia entry for Washington’s Birthday, it is part of subject of the article, or the whole subject itself.

      For people who are not GW, and for events in general, the date is the ACTUAL date the event occurred as those “missing days” never existed (all calendars being arbitrary constructions of the human mind). The Mayflower Compact was signed on 11 November 1620.

      Changing it to 22 November in subsequent official and popular records was, frankly, an illogical and absolutely unnecessary thing to do. GW’s birth day really was/is 11 February.

      Making changes at each point of information transfer generates greater chances for inaccuracy. Modern studies suggest those chances run from 3% to 6% at each transfer point. This is shown by the online editors of The Encyclopedia Britannica themselves in their entry for the Compact: they added TEN days, not eleven, to get to their posted “New Style” date of 21 November. The Britannica!!!!

      So, do NOT confuse yourself over adding or subtracting the so-called “missing days” (which, again, never existed). The original dates are the correct dates.

  7. While the change from the Julian to the Gregorian calendar and the shift of New Year’s Day from 25 March to 1 January both occurred in England and its colonies in 1752, they are nevertheless two separate matters.

    The change from the Julian to the Gregorian calendar entailed two adjustments only: (1) the deletion of eleven days to correct the error that had accumulated over the previous seventeen centuries (2 September 1752 was followed by 14 September 1752); and (2) the omission of Leap Year from future, even centuries, except those divisible by 400, to prevent a recurrence of error. The same 1750 Act of Parliament that accomplished these reforms also established that New Year’s Day would from 1752 onward be 1 January rather than 25 March. It is incorrect, however, to associate a specific calendar with the day on which the year had begun or would thenceforth begin. That these are discrete issues is illustrated by the early Romans’ use of the Julian calendar while first making 1 March and then 1 January the beginning of the year. Scotland recognized January 1 as the first day of the year as early as 1600, although they continued using the Julian calendar until the change in 1752. Clearly the date of New Year’s Day is independent of the calendar used.

    In that 25 March was/is Annunciation (or Lady) Day, the approach that puts New Year’s Day on that date is properly termed Annunciation Style but is more frequently called Old Style. Because seventh-century Romans fixed the date of Christ’s circumcision as 1 January, beginning the year on that date is accordingly designated Circumcision Style or, more frequently (beginning in 1752), New Style. The conflation of calendars and dating styles stems in part from the fact that specific changes in both occurred during the same year and resulted from the same Act of Parliament. The problem is compounded when writers use the terms Old Style and New Style in referring to both dating styles and calendars. But a careful reading of the “Dates and the Calendar” chapter of Donald Lines Jacobus’s classic _Genealogy as Pastime and Profession_, for example, confirms that they are discrete issues: when discussing the two aforementioned New Year’s days and the dating associated with each, he uses the terms Old Style and New Style exclusively and does not mention the Julian or Gregorian calendar.

    To summarize: the date on which the new year began before and after 1752 is a matter of dating style (Old Style or New Style), which is independent of the calendar used (Julian or Gregorian).

  8. I would like to offer an observation on the persistence of Old Style dating. In June 2014 I visited the remote Skye Museum of Island Life at the northern tip of the Isle of Skye in Scotland. One exhibit focused on World War 1. Included was a letter sent home from a soldier while waiting in southern England to be sent to France. His letter was dated “January 1914.” I had read the letter, walked away, and then something bothered me about it. Since the war started in August 1914, he couldn’t have been writing in January 1914. The probable explanation is that he was still using Old Style dating. What we know as January 1915 was to him January 1914.

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