The Western Gregorian Calendar

Did you know you use this calendar?

Did you know that the calendar we use today is the western Gregorian calendar?

numbered calendar

To the average person, a calendar is a calendar. 

The Gregorian calendar is based on tedious precision to ensure dates, times, the solar system and a host of other factors keep us on track 365 days a year. 

Types of Calendars

Every type of calendar has some form of time error resulting in an inexact 365-day period.

With that said, why was the Gregorian calendar chosen?

Type of Calendar

Year Introduced

Days In A Year

Error Of Time In A Year



365.2425 days

27 seconds per year


1923 (revised)

365.242222 days

2 seconds per year


2000 BC

365.242036 days

13 seconds per year


9th Century

365.246822 days

7 minutes per year


2nd Millennium BC

365.2421986 days

.5 seconds per year


25 BC

365.25 days

11 minutes per year

The Gregorian calendar was chosen by the International Organization for Standardization (ISO).

The ISO streamlines date/time into a standard for worldwide use. This standard maintains a specific format of date/time.

Not all countries use the Gregorian calendar.

This can cause confusion and error in communications with countries using a different calendar.

The History Behind The Gregorian Calendar

The Gregorian calendar was named after Pope Gregory XIII who introduced this calendar to the world on February 24, 1582.

This calendar is based upon the following:

  • 365 days per year
  • A division of time would be made
  • 12 Months
  • 11 months would have 30 or 31 days
  • The second month would have 28 days (every 4 years an extra day was added for leap year.)
  • 12 Months would be divided into 7-day increments called a “week.”
  • Each week would begin on a Monday.
  • The “western” Gregorian calendar (U.S. and Canada) starts on Sunday

The Gregorian calendar was created by the Pope to replace the Julian calendar.

The Julian calendar was created by Julius Caesar in 46 BC. 

Caesar created the Julian calendar for all of the Roman-ruled areas. However, this calendar did not reflect time correctly.

To help you better understand the difference between the Julian calendar and the Gregorian calendar, see the below.

Julian Calendar

⦁Was not planned around the earth's orbit around the sun
⦁Time was inaccurate

Gregorian Calendar

⦁Planned around earth's orbit around the sun
⦁Time is more accurate
⦁Seasons and daylight hours were taken into consideration

Countries Slowly Adopting The Gregorian Calendar

Once the Pope introduced the Gregorian calendar, Catholic countries adopted the Gregorian without hesitation.

catholic church

It took up to the 19th century for other countries to do the same.

Protestant Countries Hesitant to Adopt Gregorian Calendar

Protestants feared that the Gregorian calendar was a ploy by the Catholic Church to depress their presence.

It took England and American colonies 200 years after the Gregorian calendar was introduced to adopt it as their calendar.

Britain Loses 12 days After Switching to Gregorian Calendar

Britain replaced the Julian calendar with the Gregorian calendar on September 2, 1752.

british flag

When they went to bed and woke up the next morning, it was September 14, 1752. They had lost 11 days!

No Calendar Is Perfect

Regardless of what calendar is used, there will always be a discrepancy in time.

The perfection sought in trying to “plan time” may be beyond man’s ability.

As technology continues to grow, there may be a point in the future where man will find that “sweet spot” in narrowing planning time down to a mere milli-second or less!

Fun Facts About Calendars!

  • Pope Gregory XIII introduced the Gregorian calendar in 1582 because Easter was falling further away from the spring equinox through the use of the Julian calendar.
  • The Gregorian calendar is off by 26 seconds today because of the lack of seasonal syncing. By the year 4049, the calendar will be one full day ahead of the solar year.
  • After Britain adopted the Gregorian calendar and lost 12 days, riots and protests broke out all over the country. Those rioting demanded that they be given their 12 days back!
  • Prior to our adopting the Gregorian calendar, New Year’s was on March 25th instead of January 1st.


Kelechava, B. (2016 February 10) History of the Standard Gregorian Calendar, American National Standards Institute, Retrieved from:

Thorsen, S. (n.d.) How Accurate Are Calendars?, Retrieved from: