Calendars Explained

What could be simpler than a calendar? The printed one from the local real estate office shows twelve months, each with 28 to 31 days. Simple, right?

Well, it hasn’t always been so simple. After all, I keep stumbling upon genealogy records that are logged with “double dates.” That is, a birth record might state “22 February 1732/3.” Which was it: 1732 or 1733? Well, it actually was both. Just to make things more complex, back in those days, most of our ancestors didn’t know what day it was. You see, most people in the early 1700s and earlier were illiterate. They couldn’t read a book, much less a calendar. Most people did not know what day it was or even how old they were. Very few remembered their own birthdays.

Throughout history, learned men kept track of the days, months, and years in a variety of ways. The ancient Egyptians began numbering their years when the star Sirius rose at the same place as the Sun. The Egyptian calendar was the first solar calendar and contained 365 days. These were divided into twelve 30-day months and five days of religious festival.

The calendar used by the ancient Greeks was based on the Moon and is known as the Metonic calendar. This calendar was based on 235 lunar months that made up almost exactly 19 solar years. This 19-year cycle became known as the Metonic cycle. However, given a nominal twelve-month year, an additional lunar month was needed to synchronize the cycle. These were added in years 3, 5, 8, 11, 13, 16, and 19 of the cycle. The Greek calendar was modified several times over the years to compensate for its inaccuracies.

The original Roman calendar was a mess. It originally started the year with the vernal equinox and consisted of 10 months (Martius, Aprilis, Maius, Junius, Quntilis, Sextilis, September, October, November, and December) for a total of 304 days. The 304 days were followed by an unnamed, unnumbered period, simply called “winter.” The Roman emperor Numa Pompilius (715-673 BC) introduced February and January between December and March, increasing the length of the year to 354 or 355 days.

In the year 46 BC, Julius Caesar reformed the calendar to a more manageable form. The Julian Calendar consisted of cycles of three 365-day years followed by a 366-day leap year. New Year’s Day was celebrated on March 21, the vernal equinox (first day of spring). The calendar was called the Julian Calendar, named after Julius Caesar.

The Venerable Bede, an English scholar who lived from 673-735, noted that the vernal equinox had slipped three days earlier than the traditional March 21. He proposed changes to the calendar, but the changes were not adopted for another 850 years.

By the year 1582, the calendar had slipped to become eleven days off. To make up the difference, Pope Gregory XIII decreed that the day after October 4, 1582, would be October 15, 1582. In other words, everyone lost eleven days. Because of Pope Gregory XIII’s decree, the new calendar came to be known as the Gregorian Calendar.

The Catholic countries of France, Spain, Portugal, and Italy followed this decree immediately. Various Catholic German countries (Germany was not yet a unified nation), Belgium, the Netherlands, and Switzerland followed within a year or two, and Hungary followed in 1587.

The Protestant German countries adopted the Gregorian reform in 1700. By this time, the calendar trailed the seasons by twelve days. England finally adopted the Gregorian Calendar in 1752, declaring that Wednesday, September 2, 1752, was immediately followed by Thursday, September 14, 1752. America was a part of England at the time, so the Americans adopted the new calendar on the same date. Their neighbors in Canada had always used the Gregorian Calendar because the land had been settled by the French, who had used the new calendar since 1582. In the 1600s and early 1700s, crossing the border from the British Colonies to the French Colonies meant a change of eleven or twelve days on the calendar!

Turkey and Russia did not change to the new calendar until the early twentieth century. In Greece, 9 March 1924 was followed by 23 March 1924.

Sweden decided to make a gradual change from the Julian to the Gregorian Calendar. By dropping every leap year from 1700 through 1740, they gradually omitted the eleven superfluous days.

The year 1700 (which should have been a leap year in the Julian Calendar) was not a leap year in Sweden. However, by mistake, the Swedish government listed 1704 and 1708 as leap years. This left Sweden out of synchronization with both the Julian and the Gregorian world, so they decided to go ”back” to the Julian Calendar. In order to do this, they inserted an extra day in 1712, making that year a double leap year! So in 1712, February had 30 days in Sweden. Babies born the last day of that month had a very unique birthday!

Some religious sects still use a lunar-based calendar to determine holidays. Easter, for instance, generally occurs on the first Sunday following the first full moon after the vernal equinox, although the actual scheme is a bit more complicated.

To summarize, the Julian Calendar was slightly too long, causing the vernal equinox to slowly drift backwards in the calendar year. The Gregorian Calendar system dealt with these problems by dropping a certain number of days to bring the calendar back into synchronization with the seasons, and then slightly shortening the average number of days in a calendar year by omitting three Julian leap-days every 400 years. Even the Gregorian Calendar we use today is not perfect: astronomers and mathematicians tell us that it is off by one day every 4,000 years.

Under the older Julian Calendar system, while New Year’s was celebrated on March 21, the calendar actually began with January. Therefore, any date between January 1 and March 21 was written as a combination of two years. A child born in what is now the United States on February 3 in what we now call 1726 would have a birth date of 3 February 1725/6. Even more confusing, dates between January 1 and March 21 in a year ending in a nine would have a “/0” added, as in 3 February 1729/0. The dates written with a slash followed by another digit are referred to as “Old Style” dates.

Of course, the loss of eleven or twelve days on the calendar certainly confused the calculations often found on tombstones proclaiming that someone died at the age of 76 years, 4 months and 12 days!

When researching old records, the genealogist may often encounter “Old Style” dates such as 3 February 1727/8. Recording such dates on paper is usually simple. However, computer programs may have difficulties.

All of the better genealogy programs of today can accept Old Style dates such as 3 February 1727/8. They will even properly calculate ages from tombstone information listed as “3 February 1729/0.” In fact, most genealogy programs written in English will assume that any date entered prior to September 14, 1752 is a double date year. At least one genealogy program allows the user to specify a different year as the date of conversion from the Julian Calendar to the Gregorian. The problem is that all the dates stored in that program get converted!. This is fine for anyone who has all ancestors living in any one country, but it creates a problem for those of us with ancestors from two, three, or more countries.

For instance, my English-speaking ancestors all converted from Julian to Gregorian on September 14, 1752. However, my French-speaking ancestors converted their calendars about one hundred seventy years earlier, on October 15, 1582. If I had Russian ancestry, they would not have converted until 1917. Then there are the Swedes… . What is a person of international ancestry to do?

You can convert Julian dates to Gregorian and vice-versa at Since this is a web site in English, it seems to use the English date of September 14, 1752, as the date of conversion.

You can read more about calendars at


Steve Morse has a number of items on this subject, both conversions and explanantions.


Prior to 1752, the first day of the new year in England and her colonies was March 25 (Lady Day) not March 21. But the whole of March was considered the 1st month and February the 12th month. It is especially important to be aware of the pre-1752 calendar peculiarities when dealing with records of the Society of Friends (Quakers) as they generally did not record the names of the months, but rather used their numbers. Thus if an event was recorded as occuring on the 4th day of the 11th month 1733, for example, the uninformed would mistakenly translate this as 4 November 1733. But it is properly translated as 4 February 1733/34.

Liked by 1 person

    Can you please clarify the 11th month concept? If February is the 12th month, wouldn’t the 4th day of the 11th month be January 4? The reason for the question is that I am trying to interpret a number of similarly styled dates, with 17th day of the 5th month, 1671, as a good example. Would this be July 17, 1671?


    —> If February is the 12th month, wouldn’t the 4th day of the 11th month be January 4?

    Yes. Exactly.


    Thank you. That makes sense. The comment I had replied to would therefore be inaccurate.


Great article! The issues I have found with the 2 calendars is when I encounter a single year entry on a site such as findagrave, I am never sure if the creator of the memorial or document adjusted it to the post 1752 Gregorian calendar convention, or pulled the date from an old record that existed before 1752. As you mentioned, since most people were illiterate and had limited awareness of dates, it’s probably an insignificant problem. As an aside, my Russian born grandparents never changed their birthdates to the Gregorian calendar after they came to the US in the early 1900s.


Thank you so much for all the research you do and share with others. ‘Calendars Explained’ is so interesting and helpful. Sincerely..Fran P.


David Paul Davenport October 19, 2019 at 2:28 am

I would really like to go back to starting the new year in March. As it currently stands New Year’s Eve is too close to “Christmas Eve” and more importantly I find myself questioning whether the winters months should be thought of as the end of one year or the beginning of the new one. Could we start a petition?


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