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The International Fixed calendar (also known as the International Perpetual calendar, the Cotsworth plan, the Eastman plan, the 13 Month calendar or the Equal Month calendar) is a proposal for calendar reform providing for a year of 13 months of 28 days each, with one day at the end of each year belonging to no month or week.
The calendar year has 13 months each with 28 days plus an extra day at the end of the year not belonging to any month. Each year coincides with the corresponding Gregorian year.
The months are named the same as for the Gregorian calendar except that a month called Sol is inserted between June and July.
The first day of each year, January 1, is deemed a Sunday and every subsequent day that belongs to a month is deemed to be in the conventional 7-day week (the days of which go, in order, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday, followed by Sunday of the next week).
Days that do not belong to a month are deemed to be outside the week and always occur between a day deemed Saturday and a day deemed to be Sunday.
Since each month consists of exactly four weeks, the first day of each month and every seventh day after that for the rest of the month is deemed to be a Sunday, the second day of each month and every seventh day after that for the rest of the month is deemed to be a Monday, and so on. Therefore, each month begins on a Sunday and ends on a Saturday, just like each conventional week.
This causes all months to look like this:
The 13 months and extra days occur on the following Gregorian dates:
|January||January 1||January 28|
|February||January 29||February 25|
|March||February 26||March 25*|
|April||March 26*||April 22*|
|May||April 23*||May 20*|
|June||May 21*||June 17*|
|Leap Day||June 17|
|Sol||June 18||July 15|
|July||July 16||August 12|
|August||August 13||September 9|
|September||September 10||October 7|
|October||October 8||November 4|
|November||November 5||December 2|
|December||December 3||December 30|
|Year Day||December 31|
*These dates are a day earlier in a leap year.
The International Perpetual calendar is based on the Positivist Calendar published in 1849 by French philosopher Auguste Comte (1798-1857). Comte based his calendar on Polynesian calendars. The main difference between the International Perpetual calendar and the Positivist calendar is the names Comte gave to months and days. Positivist weeks, and Positivist months, begin with Monday instead of Sunday. Whereas the Positivist and Sol calendars place the leap day at the end of the leap year, the International Fixed Calendar and the World Calendar both place it after June.