TODAY in HISTORY – The Gregorian Calendar Explained

by William “Doc” Halliday

Do you see something odd about the calendar shown above? Let’s go back a little earlier. If you “Google” Ethan Allen you will find his birthdate listed as January 21, 1738 [O. S. January 10, 1737]. Why are eleven days missing from the calendar for September of 1752, and why are there two different dates of birth for Ethan Allen?

In 46 BC, Julius Caesar introduced the Julian calendar which took effect in 45 BC. It replaced the Roman calendar that had been used since the founding of Rome. In the ninth century, European countries began celebrating the first day of the year on March 25 to coincide with the Annunciation. England joined the trend later in the twelfth century.

The Julian calendar was not precise, and in an effort to be more accurate, Inter gravissimas was issued by Pope Gregory XIII five hundred and thirty-four years ago today, on February 24, 1582. This papal bull was meant to modify the Julian calendar, but did create a new calendar. Ten days were dropped from October 1582 and leap years occurred less often. The Gregorian calendar is 0.002% more accurate than the Julian calendar and is the most utilized civil calendar internationally.

People and governments are slow to accept many changes. Although Pope Gregory’s reform was enacted in the most solemn of forms available to the Church, the bull had no authority beyond the Catholic Church and the Papal States. The changes that he proposed were changes to the civil calendar. The pope had no authority over civil issues. They required adoption by the civil authorities in each country to have a binding legal effect. Between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country (Greece; with February 15, 1923, a Wednesday, followed by March 1, a Thursday) adopted it, it was often necessary to indicate the date of some event with a double date. This double date would reflect the New Style date and the Old Style (O.S.) date. Thus, Ethan Allen’s date of birth is listed as January 21, 1738 [O. S. January 10, 1737].

England was predominately a Protestant country, not Catholic. Thus England and her colonies remained on the Julian calendar for almost another two centuries. The Calendar (New Style) Act 1750 which was also known as Chesterfield’s Act reformed the calendar of England and her Dominions changing the new legal year to begin on January 1, rather than March 25. It also adopted the use of the Gregorian calendar putting that country and her possessions on the same basis as most of Europe.

The Parliament found that the Julian calendar then in use, and the start of the year on March 25, were “attended with divers inconveniences, not only as it differs from the usage of neighbouring nations, but also from the legal method of computation in Scotland, and from the common usage throughout the whole kingdom, and thereby frequent mistakes are occasioned in the dates of deeds and other writings, and disputes arise therefrom.”

This alignment required that 11 days be skipped in order to make up for the lack of leap year adjustments. The deletion of 11 days occurred in September of 1752 as evidenced vy the calendar at the beginning of this article.

Historians and other readers of history should be aware that the adoption of the Gregorian calendar did not take place in England and the colonies until 1752. Thus, when John Winthrop’s father wrote in his diary in 1620, “The new year beginneth”, it was on March 25. Historians generally list both Old Style and New Style dates for pre-1752 records. So you should be careful how you date! An example of the proper sequence of months during the time the Old Style was in use would have been: December, 1626, January 1626, February 1626, March 1626, April 1627…

And remember September of 1752, as it may be the answer to a trivia question.

William “Doc” Halliday is an historian and writer. He can be contacted at

William "Doc" Halliday

Historian, Political Commentator

2 thoughts on “TODAY in HISTORY – The Gregorian Calendar Explained

  • February 24, 2016 at 5:07 pm

    Very nice format,well done Doc, I’m glad you started out of FB. I’m trying to back off myself. Too many,strange things. Thanks for keeping me abreast of the situation. And very interesting about GregoryXIII.

    • February 26, 2016 at 1:34 am

      Thank you.


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