International perpetual calendar

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As International Fixed Calendar ( Engl. International Fixed Calendar , abbreviated IFC ) is a calendar design from Moses Cotsworth called (1859-1943), which this 1923 has presented. The calendar is also known under the names 13-month calendar , Cotsworth plan , Eastman plan and Eastman calendar . The calendar is very similar to the positivist calendar developed by Auguste Comte in 1849 , but was developed against a completely different background.


In the 1920s and 1930s the demand for a reformed modern calendar to replace the Gregorian calendar , which was perceived as too complicated, grew worldwide . In 1923, Cotsworth took up the 75-year-old so-called positivist calendar by Auguste Comte again, but freed it from its ideological ballast. That same year, Cotsworth founded the International Fixed Calendar League (IFCL) , an organization whose mission was to popularize the calendar he designed and to promote its introduction.

The basic principle of the calendar

This calendar divided the year into 13 months of 28 days each plus an extra day at the end of the year (also referred to as "a year and a day" for a lunar year and a day). This extra day (→ Epagomene ) is not assigned to a month or a weekday. This way the week and month stay synchronized; that is, every month begins with a Sunday and consists of four full weeks.

Calendar sheet for any month
So Mon Tuesday Wed do Fr. Sat
1 2 3 4th 5 6th 7th
8th 9 10 11 12 13 14th
15th 16 17th 18th 19th 20th 21st
22nd 23 24 25th 26th 27 28

The month names correspond to those of the Gregorian calendar. The additional thirteenth month is placed in the middle of the year between June and July and is named Sol ("Sun") or Midi ("Middle"). The length of the year, the switching regulation , the beginning of the year and the year count were also adopted from the Gregorian calendar . Cotsworth tried not to provoke a break with the Judeo - Christian calendar tradition, but only to improve the Gregorian calendar in some places. He omitted any ideological coloring of his calendar - a problem with which Comte's draft of 1849 always struggled.

Comparison of IFC months with the Gregorian calendar
  Month name Gregorian calendar
Beginning The End
1 January January 1st January 28th
2 February January 29th February 25
3 March February 26th 25th March*
4th April 26th of March* April 22nd *
5 May April 23 * May 19 *
6th June May 20 * 17th of June*
7th Sol / midi 18th of June 15th of July
8th July 16th of July 12. August
9 August 13 August the 9th of September
10 September September 10 October 7th
11 October 8th October November 4th
12 November November 5th 2. December
13 December 3rd of December 30th of December
  (Extra day)   December 31

* In leap years, these dates are one day earlier. The leap day is inserted as an extra day between Saturday, June 28th and Sunday, the 1st Sol. Just like the extra day at the end of the year, it is outside the weekly cycle and does not belong to any month.

Advantages and disadvantages

A major advantage of the calendar is that all months are structured the same, both in terms of their length and the assignment of the days of the week. So week and month are in phase. The calendar is thus structured extremely clearly. In addition, monthly events - for example the payment of salaries - could take place regularly.

The opponents of the calendar draft by Cotsworth criticize, among other things, the indivisibility of the number 13. This makes it impossible to divide the year into statistically meaningful sections such as half-years or quarters. Integrating the traditional seasons into the calendar is also difficult. The interruption of the weekly cycle is not acceptable for Judaism , Christianity and Islam .

Finally, the deletion of a total of 30 traditional calendar day dates (29th, 30th, 31st January, 29th, 30th, 31st March, etc.) causes acceptance problems. Many anniversaries such as national holidays would be eliminated.

The development of the project until 1937

When a National Calendar Simplification Committee was established in the United States in 1929 , chaired by George Eastman , IFCL managed to make its calendar the panel's favorite. In the period that followed, Eastman actively promoted the introduction of the International Perpetual Calendar, which earned it the name Eastman Calendar in the USA . Despite numerous supporters from politics and business, Eastman and Cotsworth did not succeed in pushing through the new calendar.

When the League of Nations looked for proposals for a calendar reform in the 1930s , Cotsworth's IFC was considered the most promising draft for several years until the so-called world calendar was presented in 1937 , which with its 12-month system was more oriented towards tradition. Now that the world calendar was generally favored, the IFC quickly disappeared from public discussion. The IFCL was dissolved just two years later.

Differences to the Positivist Calendar

The differences to the positivist calendar consist on the one hand in the choice of month names (the international perpetual calendar uses the classic month names - with the exception of the month of Sol - while the months of the positivist calendar are named after famous personalities from antiquity to the 19th century are), on the other hand in the placement of the leap day: In the international perpetual calendar, the leap day follows June, in the positivist calendar on New Years day.


A variant of the International Perpetual Calendar is the New Earth Calendar . The main difference to the IFC is the lack of extra days. Instead, a leap week is added to December every five years . This means that the weekly rhythm is not interrupted. Also, the additional month is called Luna , not Sol / Midi . The New Earth calendar could already be used if you equated your first seven days with the first calendar week.

A leap week is also used in the Pax calendar . However, it is not attached to December, but stands in front of it as an unofficial 14th month with the name Pax . Before the leap week or December there is the additional 13th month, which is called Columbus here .

The Sol calendar is a simpler variant . He dispenses with a leap week and inserts the extra day and the leap day into December.

The Jaktober calendar , however, goes much further . With him, the additional days are at the beginning of the year, with the extra day (written 0/0) always on the day of the winter solstice . In this way, the seasons can be distributed more precisely on the calendar. The leap day (written 0/1) is inserted after the extra day. This is done according to the switching rule of the Persian calendar , i.e. 8 switching operations in 33 years. In addition, the Jaktober calendar introduces a new era, which begins with the winter solstice 2012 ( December 20th ), as the Mayan calendar ended on this day and a new age ( Aquarius age ) began. The years before December 20, 2012 are accordingly referred to as before the Maya ( Antes Maya = AM ) and the years after that as postmaya ( Post Mayan = PM ). In addition, the 13th month in the middle of the year is called Jaktober. The films 2012 and 2012: Doomsday and the television series 2012 - The Year Zero also refer to the end of the Mayan calendar on December 20, 2012 .

Calendar 13 by Cody Jassman is a mundane variant of the Jaktober calendar . Like this, it begins with the winter solstice. However, he does not introduce a new switching rule and time calculation, but uses those of the Gregorian calendar. He also has no month names, but simply counts them.

See also

Web links

Individual evidence

  1. Official website
  2. New Earth Calendar in the Calendar Wiki , English
  3. Official website  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , English@1@ 2Template: dead link /  
  4. Pax calendar in the calendar wiki , English
  5. Sol calendar in the calendar wiki , English
  6. Official website , English
  7. Jaktober calendar in the calendar wiki , English
  8. Official website ( Memento of the original from October 16, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (English) @1@ 2Template: Webachiv / IABot /
  9. Calendar 13 in the calendar wiki (English)