There are several different calendars used around the world today. Even though advanced technology (like the internet and telephones) allows us to schedule time with other people across great distances, those same people may still track time differently. And although your grandparents probably used the same type of calendar you do, your distant ancestors probably used older calendar systems, such as the Julian calendar.
But how is your calendar different from the one your ancestors used? And why did it change? A calendar is a system that organizes days, often based on regular changes in the world around us, such as the appearance of the moon and sun in the sky. More accurate ways to measure changes in the world and different rules or discoveries made by historical leaders and great thinkers have changed calendars over time. This has led to some calendars falling out of use and new ones being adopted.
Let’s take some time to learn more about the Julian Calendar, a significant calendar in the world's history, including how it compares to other calendars and where you might encounter "Old Style" Julian dates even today.
What Is the Julian Calendar?
The Julian Calendar is named after Julius Caesar, who introduced the idea in Ancient Rome around 46 BC. The Julian Calendar determines the date based on the movement of the earth around the sun (which means it is a solar calendar). It includes 365 days in most years, but every 4 years, it also includes a leap year that has 366 days. During certain times in history, the Julian Calendar was called the "Old Style" calendar.
Why Was the Julian Calendar Created?
In Ancient Rome, during the time of Julius Caesar, the calendar being used was the Roman Calendar (an even older calendar than the Julian). The Roman Calendar was a very complicated system of dates based on the movement of the moon and the position of the sun in the earth's sky (making it a lunisolar calendar). A group of people was needed to decide when days should be added or removed to the calendar to keep it in line with the seasons of the year. The Roman Calendar started off with 304 days and used 10 months. It was used for hundreds of years and was changed many times. It wasn’t very accurate, though, and by the year 46 BC, the calendar was three months ahead of the solar calendar, and the seasons were not lining up!
That’s when Julius Caesar decided that there needed to be a big change in how the Romans determined the date. Caesar received help from Sosigenes, an Alexandrian astronomer, who advised him to stop using a lunar calendar and start following the solar year, as the Egyptians did. So instead of following the moon to determine the dates, the Julian Calendar would now follow the position of the sun in the earth's sky.
The basic structure of the Julian calendar is one that many people are familiar with today. The year has 365.25 days, is divided into 12 months, and includes leap years. It was not used everywhere in the world, but it was greatly adopted by the Roman empire and a number of Christian churches. This means it was heavily used in Europe and even extended to some parts of Western Asia and Northern Africa.
How Long Did the Julian Calendar Last? The Gregorian Calendar Replaces the Julian
Although the Julian Calendar was a big improvement from the Roman calendar, it still wasn’t perfect. The Julian Calendar was used for over 1,600 years, but as centuries passed, things started to seem a little off. It was discovered that the calendar was miscalculating the length of the solar year by 11 minutes. That 11 minutes added up year after year, and by the 1570s, astronomers realized that the Julian Calendar was now off by 10 days.
With the help of both an astronomer and mathematician, a man named Pope Gregory XIII created a new calendar called the Gregorian Calendar, which is actually very similar to the Julian Calendar but has some updated calculations. Because of these updates, most people use the Gregorian Calendar today. Here are some of the differences between the 2 calendars:
Different Definitions of a Year
The Julian Calendar defines a year as 365.25 days long (an extra ¼ of a day).
The Gregorian Calendar defines a year as 365.2422 days long. This calculation is more precise than the Julian Calendar.
Different Leap Year System
The Julian Calendar uses a simple formula to determine leap years. The leap year system adds an extra day every 4 years to add up to that full extra day. This pattern of 3 “normal years” followed by 1 “leap year” was repeated without exception.
The Gregorian Calendar uses a more advanced formula for its leap year calculations. The rule is that if the year is divisible by 100 and not divisible by 400, leap year is skipped. The year 2000 was a leap year, for example, but the years 1700, 1800, and 1900 were not. The next time a leap year will be skipped is the year 2100.
Fun Fact: The next upcoming leap year is 2024.
Different Level of Accuracy
The Julian Calendar was off by 11 minutes every solar year, which added up and made us lose 10 days by the year 1582.
The Gregorian Calendar is much more accurate and is only off by 26 seconds every solar year, which will eventually add up to make us lose 1 day by the year 4909.
350 Years of Double Calendars
Even though the Gregorian Calendar was created in 1582, hundreds of years passed before it became the calendar most people use. Many countries were resistant to the new calendar and preferred to keep using the Julian Calendar as long as possible. This created a time in history where both calendars were used regularly in different parts of the world, with different countries and peoples starting to use the new calendar at different times. During this time period, those who tried to clarify between the 2 date systems would often write "Old Style" next to Julian dates and "New Style" next to Gregorian dates.
Here’s an example from Matt Rosenberg on ThoughCo:
“In the era after the change, dates were written with O.S. (Old Style) or N.S. (New Style) following the day so people examining records could understand whether they were looking at a Julian date or a Gregorian date. While George Washington was born on February 11, 1731 (O.S.), his birthday became February 22, 1732 (N.S.) under the Gregorian calendar.”
From 1582 to around 1923, there were still enough people using the Julian calendar to consider it a time of overlapping dates. That’s almost 350 years of both calendars being regularly used! (Some peoples and organizations still used the Julian calendar after 1923, but most had switched over.)
Activity Idea: Which of your ancestors might have been alive during the years of the double calendars? Try connecting to the shared Family Tree on FamilySearch to learn where and when your ancestors were born. You can even see their life events on a time line and an interactive map—all with a free account!
Get Started with FamilySearch
How to Convert Julian Dates to Gregorian Dates When Doing History Research
You can still find and read documents with Julian dates in them, without being a historian or visiting a museum. Most of these are digital images of old documents, the kind you'd find while doing primary source research or searching for an ancestor's name in historical records.
Maybe you’re working on a homework assignment or maybe you’re doing some family history research. Either way, if the date you’re looking for falls before 1582 or 1923 and you suspect it's a Julian date, it’s helpful to know how to find the corresponding Gregorian date.
There are several helpful converters online. Here are 2 that might help you do a conversion quickly:
- Fourmilab Calendar Converter
- Includes many different calendar conversion options. Find the right type of calendar for the date you want to convert, set the date, and scroll up and down the page to see how that date would look in the different calendar systems.
- Stevemorse.org Julian to Gregorian Converter
- Converts just Julian to Gregorian but also includes an easy tool to see when different countries switched over.
If you like math, you might be interested in trying a conversion yourself. Click here to see how the calculations work.
Sometimes converting Julian dates to Gregorian is as simple as adding 13 days to the Julian date, but that depends on what years you are working with. Here’s a more accurate way you can calculate the a Gregorian date:
- Take off the last two digits of the year (for example, for the year 1700 or 1712, just look at the 17).
- Take that number and multiple it by 0.75.
- Then subtract 1.25.
- Drop any digits to the right of the decimal point.
- That result is the number of days to add to the Julian date to get its equivalent Gregorian date.
Here is what this might look like for the date January 2, 1712:
- We take "1712" and convert it to "17".
- 17 x 0.75 = 12.75
- 12.75 - 1.25 = 11.5
- 11.5 becomes 11 when we drop the decimals.
- The Julian date, January 2, 1712, then becomes the Gregorian date, January 13, 1712.
Note: For a BC date, you will need to subtract 1 from the year before following these steps and add the year back in at the end of the steps.
Doing Family History with Julian Dates
Did you know that many families can find documents with their ancestor's names back into the 1800s or even 1600s? Modern technology makes it a lot easier than it used to be. Doing simple online searches for old documents is something you can now do from home. You don't have to be a historian to try! Start with the name of a grandparent or ancestor that you know, and try it for free on FamilySearch.org.
FamilySearch has many resources to help you find documents for your ancestors. For example, beginners can get good research tips here. If you like history or family history a lot, you might be interested in this article on the FamilySearch wiki that tells you the approximate years when different countries switched from the Julian to Gregorian calendars.
Activity Idea: Try to find the oldest ancestor your family can remember. Start by talking to your parents, grandparents, or another family member you know well. Do they know the name of any of your grandparents or great-grandparents? What about any ancestors further back? You can use one of these free templates to record what you learn:
Free Family Tree Templates
Is the Julian Calendar Still Used Today?
The Julian Calendar was helpful when it was created, but it’s not used much anymore. The Gregorian Calendar is simply more accurate, so that's what most countries use today.
Some Orthodox churches, like the Orthodox Church in Russia, still use the Julian Calendar today to calculate the dates of moveable feasts. Others who still use the "Old Style" calendar include the Berber people of North Africa and on Mount Athos.
Even though different calendars are used around the world, there’s one thing they all have in common. Calendars help us record our history. Keeping track of the date helps us remember important people and important events.
One Last Activity Idea: If doing history research isn't what you like to do, take some time to record your own life events. Writing down what you know might help someone in the future connect to your family's story. Here's a tool that can help:
Record Your Memories
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