What Calendar System Does Most of the World Use? • FamilySearch (2024)

Did you know that calendar systems have been evolving throughout history? The calendar most people use today isn’t the same as the one used by Julius Caesar or the ancient Egyptians.

Calculating dates is not an exact science, as calendars can be based off of different things. Even today, many calendar systems are used around the world. But if you ask, “What calendar do we use?” the answer will usually be the Gregorian calendar—as this is the calendar most people use for business and often for everyday dates.

Let’s learn what the Gregorian calendar is, how it became the most common calendar, which countries use or don't use it, and what happened during the years of “double calendars.” We’ll even teach you how to figure out if your ancestors used the same calendar we do!

Fun fact: For many following the Gregorian Calendar, the New Year is celebrated on January 1 of each year. Although China uses the Gregorian calendar for everyday dates, they use the traditional Chinese Calendar for holidays. This means they celebrate the New Year on a different day each Gregorian year.

What Is the Gregorian Calendar?

The Gregorian Calendar is a system for determining the date that was introduced by Pope Gregory XIII in the year 1582 AD. It is based on the movement of the earth around the sun (which means it’s a solar calendar) and includes leap years. (A leap year refers to a year when an extra day is added to the calendar to help with accuracy over time.) This calendar is sometimes referred to as the ”New Style” calendar, making it different from the “Old Style” Julian Calendar.

Why Was the Gregorian Calendar Created?

Just before the time of Pope Gregory XIII, the calendar being used by the Romans and many Christian churches was the Julian Calendar. Put into effect by Julius Caesar in 46 B.C., the Julian Calendar was also a solar calendar that included leap years. This calendar worked well over the years, but as centuries passed, the calendar date and the season of the year seemed to be getting out of sync.

For example, it’s been suggested that the original goal of the Gregorian Calendar was to correct the date for Easter, which seemed to be getting further and further away from the spring equinox. With help from astronomers and mathematicians, they figured out that the Julian Calendar was miscalculating the length of the solar year by 11 minutes. That 11 minutes added up year after year, and by the 1570s, Pope Gregory XIII and his peers realized that their calendar was off by 10 days!

It became pretty obvious that a new calendar was needed. So, they created one that would be more accurate over time. In 1582 AD, this new, “Gregorian Calendar” was introduced, named after Pope Gregory XIII, who pushed for the change. The new calendar recalculated the leap years to make the average length of a year more accurate.

Once they knew why the calendar date and the season of the year were off, it was time to get back on track. To make up for the lost 10 days from the Julian Calendar, the Gregorian Calendar simply moved up the date to skip 10 days. So, when the people went to sleep 1 night, the date was October 4, and when they woke up, the date was now October 15. Can you imagine that?

Fun Fact: Astronomers today don’t use the Gregorian Calendar in their work. They use a Julian Date system (not the same as the Julian Calendar!) to calculate when stars and other objects have appeared in the sky.

What’s the Big Difference between the Gregorian and Julian Calendars?

Honestly, there’s not a big difference between the 2 calendars. The Gregorian and Julian Calendars are actually rather similar in how they work. They both are solar calendars that focus on the 365-day movement of the earth around the sun and include leap years every 4 years. But here are some small, but important ways the 2 calendars are different:

• Different Definitions of a Year: As mentioned earlier, the Gregorian Calendar defines an average year as 365.2422 days long, unlike the Julian Calendar which defines an average year as 365.25 days long.
• Different Leap Year System: While both calendars use leap years systems, you’ll see a slight difference in how they work. The Julian Calendar adds a day to the calendar every 4 years. The Gregorian calendar does the same, except when the year is divisible by 100 and not divisible by 400. Then the leap year is skipped.
• Different Level of Accuracy: The Julian Calendar was off by 11 minutes every solar year. The Gregorian Calendar is only off by 26 seconds every solar year. It will eventually add up to make us lose 1 day by the year 4909. It’s not perfect, but definitely an improvement!

Fun Fact: The next upcoming leap year from the time this article was published is 2024. The next time a leap year will be skipped is the year 2100.

See Also

The Ethiopian Leap YearChinese / Lunar New Year 2024 - Awareness Days Events Calendar 2024All about the Jewish Calendar • FamilySearchGregorian calendar | Definition & Facts

350 Years of Double Calendars

Even though the Gregorian Calendar was created in 1582 AD, it took a long time for it to really replace the Julian Calendar. Many countries who used the Julian refused to use the new calendar at first and preferred to keep using the Julian Calendar as long as possible.

Hundreds of years passed before the Gregorian Calendar finally became the calendar most people use. This created a unique time in history where there were 2 dates used by some countries: a Julian date (also called an Old Style date) and a Gregorian date (also called a New Style date).

There were almost 350 years of overlapping dates between the 2 calendars, ranging from 1582 AD to the 1920s AD. Different countries adopted the Gregorian calendar at different times during this period—with a few even transitioning much later. To avoid confusion during this time, historians sometimes had to write down both dates when keeping record of something.

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.”

As different countries transitioned to the Gregorian calendar at different times, not all of them transitioned in the same way. For example, by the time Great Britain adopted the new calendar, they had to jump forward 11 days instead of 10. Sweden was one country that chose to transition gradually—over a period of 40 years—by dropping days in leap years instead of all at once.

It is also good to note that many countries that used other calendars (besides the Julian) also adopted the Gregorian calendar in some form during this 350 years, but not all.

To learn more details about a specific country’s transition, Wikipedia and the FamilySearch Wiki have some helpful tables and descriptions.

How to Convert Other Calendar Dates to Gregorian Dates

You can still come across documents with “old style” Julian dates in them, without being a historian or visiting a museum—maybe while working on a homework assignment or doing some family history research. You may also encounter someone who uses the Jewish calendar, Chinese calendar, or Hindu calendar, especially for calculating religious holidays. It’s helpful to know how to change dates between the different systems.

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.

Who Uses the Gregorian Calendar Today?

Many areas of the world currently use the Gregorian Calendar or a modified version of it.

• 168 of the world’s countries use the Gregorian Calendar as their main calendar (or civil calendar) including: Australia, Brazil, France, Mexico, and the United States.
• 18 countries use another calendar alongside the Gregorian Calendar including: Algeria, Egypt, Morocco, Saudi Arabia, and Yemen.
• 4 countries use a modified version of the Gregorian Calendar. They are: Japan, North Korea, Taiwan, and Thailand.
• 4 countries have not adopted the Gregorian Calendar. They are: Afghanistan, Iran, Ethiopia, and Nepal

The Gregorian Calendar is accepted as an international standard, but it’s not the only calendar still in use. Other significant calendars in use today include the Jewish, Islamic, Indian, Chinese, Persian and Julian Calendars.

Fun fact: When Sweden switched over from the Julian Calendar to the Gregorian Calendar, they chose to add February 30th to their calendar instead of losing the 10 days. The plan was to not have leap days over the next 40 years to eventually remove the extra 10 days.

Though an Improvement, the Gregorian Calendar Still Isn’t Perfect

With the Gregorian Calendar being so widely used for hundreds of years, you would think it’s the most accurate calendar out there, right? Well, surprisingly, it isn’t.

For example, the Iranian Calendar could be considered one of the most accurate calendars in the world. The Gregorian Calendar requires a 1-day correction every 3,226 years. The Iranian Calendar, however, only requires a 1-day correction every 141,000 years.

There have been several attempts to reform the current Gregorian Calendar. One recent attempt was in 2011 by an astrophysicist named Richard Conn Henry and an economist Steve Hanke. The Hanke-Henry Permanent Calendar is a fixed calendar, where the date falls on the same exact day of the week year after year.

Although these attempts are of interest to those who seek a better or changed calendar, none have been widely adopted, and the Gregorian Calendar remains the primary calendar for most countries throughout the world.

Recording Your Own Life Events

No matter what calendar you follow, calendars can help you keep track of the seasons of the year, religious and secular holidays, and important life events. Recording dates is a valuable part of preserving history and can also help you with family history research.

Bonus Activity Idea: 

Write down or audio record your own life events—and be sure to include a date! You can even note what calendar system you are using—now that you know. By preserving your own memories, you are helping someone in the future better connect to you and your family’s story.

FamilySearch has a fun, free way for you to record your story. Try it here:

Record Your Story

See Also

Different Calendars Humans Have Used Throughout History - Calendar