If your ancestors were from Great Britain or her colonies (United States and Canada), and you are lucky enough to have dates of events for your ancestors, like a baptism or marriage that occurred before the 3rd of September 1752, you will have entered the sometimes confusing dating of the Julian (Old Style) calendar. Any date before the 3rd of September 1752, depending on the source that you came by it could be out by 11 days by modern day reckoning and if the event occurred from the 1st of January and the 24th of March of any year, then the year date will seem to be out by 1 year by modern day reckoning. If you do have events with such dates, you will have to device a system by which you can understand the dating, and when you passed such information on, you will have to also pass on the system you use.

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Julian Calendar

The Julian (Old Style) Calendar came into existence during the reign of Roman Emperor Julius Creaser. It was the first Calendar that came close to predicting the year. This calendar was created on the premise that the solar year was 365.25 days long (the correct number is 365.2422 days). For the Julian to accommodate the quarter day, a leap year was added to the calendar after every four years.

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Gregorian Calendar

The Gregorian (New Style) Calendar which we use today was enacted by Pope Gregory XIII in 1582. It was enacted because the Julian Calendar was out of step with the solar year by ten days or in other words, ten day behind the solar year. Only the catholic countries of Europe adopted the Gregorian calendar initially, only much later did the protestant countries of Europe follow. When the Julian calendar was abolished in Great Britain and it's colonies in 1752, the Julian calendar by then was eleven days out from the solar year. Another change was also made in Great Britain and it's colonies at the same time, and that was that the New Year would begin on the 1st of January instead of the 25th of March as it had prior. I do not know when the year beginning on the 1st of January for countries occurred.


The Gregorian calendar is based on the solar year being 365.2425 days long. This calendar only allows a leap year for the last year of a century if the first to digits of the year are divisible by four. So 1600 and 2000 were leap years, where 1700, 1800 and 1900 were not.


The table below shows the dates for various Countries when the change was made from using the Julian Calendar too using the Gregorian Calendar. This table is based on information that is found in the featured article of the Genealogical Research Directory (1999 edition) which was in turn was abstracted from the Society of Genealogist publication titled "Dates & Calendars for the Genealogist" (reprint 1998).

CountryWhen changed to the Gregorian Calendar
Austro-Hungarian Empire7 Jan 1584 became 17 JAN 1584
Belgium11 Mar 1582 became 21 Mar 1582
Denmark19 Feb 1700 became 1 Mar 1700
Finland18 Feb 1753 became 1 Mar 1753
France10 Dec 1582 became 20 Dec 1582 1
Germany (Some Catholic)1582
Germany (Some Protestant)19 Feb 1700 became 1 Mar 1700
Germany (Augsburg)14 Feb 1583 became 24 Feb 1583
Germany (Lousitz & Silesia)13 Jan 1584 became 23 Jan 1584
Germany (Paderborn)17 Jun 1585 became 27 Jun 1585 
Germany (Pfalz-Neuburg)14 Dec 1615 became 24 Dec 1615
Germany (Prussia)23 Aug 1612 became 2 Sep 1612 2
Great Britain and Colonies3 Sep 1752 became 14 Sep 1752
GreeceFeb 1923
Netherlands (Catholic)15 Dec 1582 became 25 Dec 1582
Netherlands (Protestant)19 Feb 1700 became 1 Mar 1700
Norway19 Feb 1700 became 1 Mar 1700
Poland5 Oct 1582 became 15 Oct 1582 3
Portugal5 Oct 1582 became 15 Oct 1582
Russia1917 4
Spain5 Oct 1582 became 15 Oct 1582
Swedenbetween 1700 and 1740 5
Switzerland (Catholic Canon)1583
Switzerland (Protestant Canon)19 Feb 1700 became 1 Mar 1700 6
  1. The Republican calendar was in use in France and it possessions and conquest from 24 Nov 1793 until 31 Dec 1805
  2. Some authorities say the change was made 1 Jan 1583
  3. Some authorities say 1586
  4. Officially, but because of the civil war, not recognised throughout the country until 1921, and not by the Russian, Greek, Serbian and Romanian churches until May 1923, when they accepted a modified Gregorian system
  5. Gradually by the omission of all Leap Years between these years
  6. Except Gallen 1724, Glarus and Appenzell 1798 and Granbueden 1798

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Genealogical research ramifications with the different Calendars

In the parish records for Emneth in Norfolk, there can be found a date of burial for my ancestor Daniel Frusher, the date reads the 14th of February 1741. This date is based on the Julian calendar dating system. The same date if corrected to the Gregorian calendar dating system would read the 25th of February 1742. This event will be found partially corrected, appearing as an hybrid form on my genealogy records as the 14th of February 1741/2. When you have found or are given a date of an event that occurred before the 3rd of September 1752 for records created in Great Britain or her colonies, you should attempt to establish if the date has been rendered Old Style or New Style. The rule of thumb for the IGI. is that all dates are rendered in New Style, but some submitters for the IGI. have not made the correction, so some dates are rendered Old Style.


The reason for knowing how a date is rendered becomes apparent with the following example. If you have found a baptism for a child that occurred on the 12th of March 1729 with parents William and Ann Johnson. From another source you have a couple William Johnston and Hannah Smith who were married on the 13th of February 1730. Which event occurred first? It all depends on how the dates are recorded. If the baptism is recorded as Old Style and the marriage is recorded New Style, then the marriage occurred first and couple William Johnston &Hannah Smith could be parents William and Ann Johnson. 

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Converting Dates

Most parish records that occurred in Great Britain and her colonies, prior to the 3rd of September 1752, are recorded in Julian (Old Style) dating. This means that you will have to make an allowances for the differences between the dating of the Julian (Old Style) and Gregorian (New Style) Calendars. To make the necessary adjustments to the dates that are prior to the 3rd of September 1752, please use the tables found below and use the columns titled Julian to Gregorian. Remember that when recording the dates, make a note if you have rendered the date Old Style or New Style.

On or before the 29th of February, 1699/1700

 Gregorian to JulianJulian to Gregorian
1st Jan - 24th Mar- 10 days, - 1 year*+ 10 days, + 1 year*
25th Mar - 31st Dec- 10 days+ 10 days

After the 29th of February, 1699/1700

 Gregorian to JulianJulian to Gregorian
1st Jan - 24th Mar- 11 days, - 1 year*+ 11 days, + 1 year*
25th Mar - 31st Dec- 11 days+ 11 days


* Due to the New Year beginning on the 25th of March (Lady's day) of each year.


Please note that when converting a date by 10 or 11 days, that you include the 29th of February for a leap year in the equation if the date you are converting falls the 10 or 11 days prior to or after the 29th of February. The years that are leaps years have their two last digits as 04, 08, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, 84, 88, 92 and 96. The years 1600 and 2000 were also leap years. The years 1500, 1700, 1800 and 1900 were not leap years.

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1st of January 2001, The first day of the New Millennium

That glorious day, being the first day of the 21st Century and the 3rd millennium. The popular belief leading up to the year 2000 was that the 1st of January 2000, was the beginning of the new millennium, and the arrival of this singular point in time was given the ambiguous name, "The Millennium." Now to believe the premise about when the new millennium began, the 1st of January 2000, you would also have to agree to the premise that there was also a year zero. Now to do so, you would have to invent the following:

  • A new Calendar
  • A new numbering system
  • A new number, zero
  • A new meaning of the word zero

You may ask if this is a continuation of the debate. Being a genealogist, and wisely knowing when each millennium or indeed when each century begins or ends can be crucial. If there is information that states that John Smith was born in the 2nd year of the 19th century, then what year is the information referring to. I would say correctly, the year 1802, but if a genealogist followed popular opinion about when each new millennium or century begins or ends, they would say 1801.


When we use dates such as the days of the month or years, what we are using to symbolise such dates are integers or whole numbers. Our system of dating, or our use of Calendars, requires us to use integers or whole numbers which are 1, 2, 3 and so forth, so as to create the man-made system and illusion called time. Now some people may belief that zero is a number, but this is incorrect, because all numbers being whole or mixed represent something, where zero represents nothing.


Zero is the points where positive and negative integers meet on an infinite imagined line (see the diagram below). Understanding this, there is no problem in understanding why some people like myself are in the opinion that the 1st of January 2001 was the first day of the third Millennium. Some people may argue that Zero does represent something, because we use it in the present era as in the years 2001 or beyond.  When we speak of the year 2001, what we are actually expressing is a year that has an integer that consist of 2 thousands, 0 hundreds, 0 tens and 1 one. The zero still represent nothing. With our system of the Calendars, the years that are represented by positive integers are referred to as being in the period A.D. which is the abbreviation of the Latin term anno Domini, meaning "In the Year of our Lord". The years that are represented by negative integers are referred to as being in the period B.C. meaning "Before Christ".

Zero is the point where negative and positive integers meet