Project by Kalyani Tupkary. Website built by Jon Packles.


Here every year is the same - with 13 months of 28 days each. Every date is fixed to the same weekday. So, the 17th is always a Tuesday.

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In a scalding-hot argument against the 12-month calendar, a September 1927 issue of The Outlook proclaimed: 'A month is a wholly irrational division of time. It has no relation to anything in astronomy, or human experience. It is an inaccurate and varying measure of time that is a constant annoyance in business and a misleading unit in science. It has no religious significance. A month is nothing but just a bad habit.'

The International Fixed Calendar is a solar calendar with 13 months of 28 days each. It is a perennial calendar as every date is fixed to the same weekday every year. Momentum behind the International Fixed Calendar, a 13-month calendar with 28 days in each month and a leftover day at the end of each year (it also followed the Gregorian rules with regards to Leap Years), was never stronger than in the late 1920s. Similar to Auguste Comte's positivist calendar (created in 1849), this particular 13-month invention came from the mind of Moses Cotsworth, a North Eastern Railway advisor bothered by inexplicably varying monthly earnings over the traditional 12-month period. In 1902, driven by a desire to simplify the ‘irrational calendar’ Moses B Cotsworth presented a solar calendar for calendar reform. His solar calendar had 13 months of 28 days each. Every date was fixed to the same weekday every year. Every week starts with a Sunday and ends with a Saturday. Cotsworth's plan quickly gained popularity among businessmen, especially in transportation and logistics. His biggest ally, however, was photography pioneer and Kodak founder, George Eastman. Impressed by the symmetry of this hyper-rational calendar, George Eastman adopted it for use in his Eastman Kodak Company 1928 to 1989 while the rest of the world followed the Gregorian calendar.

  • Image 1: The 13-month calendar as used by Kodak in 1928 and 1989. Courtesy the George Eastman House
  • Image 2, 3: A 1927 issue of "The Outlook" compares the Gregorian calendar to the International Fixed Calendar. Courtesy George Eastman House
  • Image 3: Col. Henry Stimson (left) holds the report of the National Committee on Calendar Simplification while standing next to George Eastman on August 14, 1929. AP, George Eastman House
  • Reference: Byrnes2014, Mark. “The Death and Life of the 13-Month Calendar.” Bloomberg. Accessed December 6, 2020.