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The Switch from the Julian Calendar to the Gregorian Calendar

The Gregorian Calendar, also known as the “Western Calendar” or “Christian Calendar”, is the most widely accepted calendar around the world today. Its predecessor, the Julian Calendar (*), was replaced because it did not correctly reflect the tropical year or solar year marked by Earth's revolution around the Sun. To get back in step with astronomical reality, a number of days were dropped in the new calendar, creating irregular months with only 18 days and odd dates like February 30.

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11 days were omitted in September, 1752 in some countries.

When was the Gregorian Calendar introduced?

The Gregorian Calendar was first introduced in 1582 in some European countries. However, many countries used the Julian Calendar much longer. Turkey was the last country to officially switch to the new system on January 1, 1927.

More about the Julian Calendar

More about the Gregorian Calendar

The Switch to the Gregorian Calendar in Countries around the World

The table below shows when the Gregorian Calendar was introduced in some countries and how many days were dropped.

Click on the country links to view a calendar for the irregular year, and look out for months that have some days missing.

Please note: The list shows only a small selection of countries.

YearCountryNumber of days dropped
158210 days
158310 days
158710 days
161010 days
175211 days
1872/187312 days
1911/191212 days
191613 days
191813 days
192313 days
1926/192713 days

Did you know? timeanddate.com's Calendar Generator and Printable PDF Calendars automatically take into account the different dates for the calendar change, meaning that the Julian Calendar is shown by default for years before the switch. It is possible to manually switch to the other calendar system by selecting “Gregorian Calendar” or “Julian Calendar” in the drop-down menu entitled “Country”.

Why does the number of omitted days vary?

The Julian Calendar moves slightly slower than the Gregorian Calendar, introducing an error of 1 day every 128 years. This means that the difference between the two calendar systems increases slowly over time. The papal bull issued by Pope Gregory XIII in 1582 decreed that 10 days be dropped when switching to the Gregorian Calendar. However, many countries chose to introduce the new calendar in later years. The later the switch occurred, the more days had to be omitted. Currently (years 1901 - 2099), the Julian Calendar is 13 days behind the Gregorian Calendar.

The Gregorian Calendar is not perfect either, though somewhat more precise: it is off by only 1 day in 3236 years.

Is there a perfect calendar?

Too many Leap Years

The reason why the Julian Calendar was out of step with the tropical year was the rule it used to define a Leap Year. The Julian Calendar had only one rule to determine whether a year would have 29 days in February instead of 28. If the year could be divided by 4 then it was considered to be a Leap Year. The Gregorian Calendar on the other hand has a more complicated rule for calculating what years will be Leap Years:

These rules result in fewer leap years, minimizing the inaccuracies of the Julian Calendar.

The delay in switching to the Gregorian Calendar meant that different countries not only followed different calendars for a number of years, but also had different rules to calculate whether a year was a Leap Year. This explains why the years 1700, 1800 and 1900 were considered to be Leap Years in countries still using the Julian Calendar (e.g. Greece), while in countries that had adopted the Gregorian calendar (e.g. Germany), these years were not Leap Years.


(*) Please note: The term “Julian Calendar” is sometimes used to describe a calendar showing day numbers (1 - 365/366). This article refers to the old calendar system also called Julian Calendar that was in use before the Gregorian Calendar was introduced.

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