We are independent & ad-supported. We may earn a commission for purchases made through our links.

Advertiser Disclosure

Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.

How We Make Money

We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently from our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is the Gregorian Calendar?

Jessica Ellis
Updated May 23, 2024
Our promise to you
Historical Index is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At Historical Index, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

The Gregorian calendar is used throughout most of the modern world. Invented in 1582, the system adopted a leap year cycle different than the one employed by the Julian calendar. The new calendar was considered an improvement on the earlier Julian model. In the Gregorian calendar, four years make up a cycle, with an extra or “leap” day added to the fourth year to keep the dates and months synchronized with the solar cycle.

Although the Gregorian calendar was named for Pope Gregory XIII, who sanctioned its use, it was created by an Italian doctor named Aloysius Lilius. The Julian calendar, in use for centuries, did not have a system in place to make the dates of the equinoxes, and consequently the Catholic holidays associated with them, fall on the same day. In addition to dropping ten days from the Julian system, the Gregorian calendar introduced different rules to the leap year system to establish consistent dates in relation to the equinox. This new approach allowed Christmas, for example, to fall on December 25th every year.

In the new system, there were twelve monthly divides of similar, although unequal lengths. February, the second month, was the only month to contain 28 days, so the added day in leap years was solidified as 29 February. Leap years exist once every four years, and only occur in years that are divisible by four. There is an exception to the divisible-by-four-rule, and that is if the year ends in -00. Even though years ending in -00 are divisible by four, it is not a leap year. However, there is one more exception to the exception. Years ending in -00 that can be divided by 400 are in fact leap years.

The Gregorian calendar was decreed valid by Pope Gregory XIII on 24 February 1582, but was not accepted by any European nations until October of that year. The first countries to begin mandating the use of the calendar were Spain, Portugal, Italy, and the Polish-Lithuanian Commonwealth. France and Holland quickly followed, both adopting the new method before the end of 1582.

Non-Catholic countries understandably had reservations about accepting a calendar specifically aimed at furthering the goals of the Roman church. Europe was heavily involved in the Protestant reformation when the calendar was proposed, and anti-Catholic sentiment long postponed the unification of Europe under a common calendar. Eventually, the benefits of a common date system became impossible to dismiss, and while the calendar had been created at the whim of the Catholic Pope, its scientific basis made a considerable amount of sense.

It took several centuries, but by 1929 most countries in the world had begun using the Gregorian calendar. China, the last nation to adopt the system, technically accepted it beginning in 1912, but civil unrest left the calendar question undetermined until the unification of the country in 1929. Other countries, such as Japan, accepted the use of the calendar for dealings with the western world, but still maintained local systems in place for centuries.

Typically, when talking about dates prior to the 1582 institution of the calendar, scholars continue to use the Gregorian count retroactively. Occasionally, you may come across dual dating, which uses both Julian and Gregorian years. This most often refers to the interim time when the Gregorian calendar may not yet have been accepted, but was already in wide use.

Historical Index is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Jessica Ellis
By Jessica Ellis , Writer
With a B.A. in theater from UCLA and a graduate degree in screenwriting from the American Film Institute, Jessica Ellis brings a unique perspective to her work as a writer for Historical Index. While passionate about drama and film, Jessica enjoys learning and writing about a wide range of topics, creating content that is both informative and engaging for readers.

Discussion Comments

By galen84basc — On Nov 03, 2010

Although the Gregorian calendar is obviously the most widely used calendar in the world, many people still have a working knowledge of other calendars, especially for religious or astrological purposes.

For example, even if they don't go by the dates on the Chinese calendar, many Chinese people can still tell you right off the bat when Chinese New Year is or the Mid-Autumn festival. Not to mention all the animals for the years, and when their year starts and ends.

The same holds true for the Jewish calendar. Many practicing Jews can easily tell you when Rosh Hashanah or Yom Kippur is.

I'm glad that a little variety survives, even in the small things like calendars. Makes like more interesting.

By musicshaman — On Nov 03, 2010

Did you know that before the Julian calendar, the calendar was so rarely in time with the seasons that the priests of Rome were responsible for changing it regularly?

Of course, with that kind of power they had all sorts of fun, changing dates to extend one leader's rule, or change election days at will.

Once the Julian calendar was put in place in 45 BC, a lot of that cleared up (that was also the first time New Year's day was celebrated on the first, FYI). However, since Caesar failed to account for what we now correct with leap years -- one of the biggest advantages when it comes to Julian calendar vs Gregorian calendar -- the whole thing fell out of favor again until it was replaced with the Gregorian calendar in 1572.

And my students tell me that history is boring! Even the history of the calendar is so interesting, not to mention the politics and wars!

By StreamFinder — On Nov 03, 2010

It's so weird to think about not using the Gregorian calendar. I mean, everybody has got the correlation between the seasons and the months so connected in their heads that it would feel crazy to switch from the Gregorian to the lunar calendar, for example.

I also find it really interesting to see how societies switched over. For example, you talked about the Chinese calendar, but you could also consider the change from the Persian to the Gregorian calendar, or from the Jewish to the Gregorian calendar.

I can't imagine how odd it would have been to be in one of those societies and wake up one day with a new calendar. I bet it caused no end of paper headaches and hassles.

I'm just glad that we seem to have gotten the whole calendar thing settled -- at least for my lifetime!

Jessica Ellis

Jessica Ellis


With a B.A. in theater from UCLA and a graduate degree in screenwriting from the American Film Institute, Jessica Ellis...
Learn more
Historical Index, in your inbox

Our latest articles, guides, and more, delivered daily.

Historical Index, in your inbox

Our latest articles, guides, and more, delivered daily.