Would You Accept A New Calendar With 13 Months?

The world came remarkably close to this becoming a reality at the start of the 20th century.

Russell is a Science Writer with IFLScience and has a PhD in the History of Science, Medicine and Technology

Dr. Russell Moul

Russell is a Science Writer with IFLScience and has a PhD in the History of Science, Medicine and Technology.

Science Writer

A photo of a red and white calendar on a table. The pages of the calendar are flicking as though they are blowing in the wind suggesting that time is moving.

Plans for a 13-month calendar nearly came to fruition, but eventually failed. 

Image credit: Brian A Jackson via

How would you feel about a radically different calendar, one that organized the year into 13 months, each with exactly 28 days? Well, this nearly became a reality for the world following the First World War, but people were so unhappy about it that it never came about.

Messing with time

Fiddling with calendars is not new. Throughout history, various attempts by different thinkers and institutions have attempted to devise alternative arrangements for our years. For instance, in 45 BCE, Julius Caesar added leap days – one extra day every four years – to the cumbersome and complicated Roman calendar. which relied on the phases of the moon. This new version, the Julian calendar, relied on astrological calculations that suggested a tropical year – the time from spring equinox to spring equinox – took 365 and a quarter days to complete.


Then, around 1,500 years later, this calendar was replaced by Pope Gregory XIII, introducing the Gregorian system we rely on today. But even as the world gradually adopted this new calendar over the centuries, other people were devising their own versions with different configurations of days, and in the first half of the 20th century, a new idea was proposed.

13 months is better than 12?

The idea of a 13-month calendar was first devised by Auguste Comte, the French philosopher, mathematician, and writer, in 1849. It involved arranging the calendar into 354 days a year, which included two “blank” days (based on the work of an Italian Catholic priest 15 years earlier). Each month was given 28 days, which allowed them to be organized into four exact weeks.

This calendar was known as the “positivist” calendar, but it was not very popular. This was mostly because Comte filled the days of the year with the names of various prominent men and women from history (a tribute to the leading figures in the “religion of humanity”), which made it less than appealing. However, interest in this arrangement did not go away.

At the start of the 20th century, an Englishman called Moses B. Cotsworth revised the 13-month calendar, freed it from its weighty and confusing names, and repackaged it with the additional month being labeled “Sol”.


This new plan was received with more enthusiasm, especially in America where it became known as the Eastman plan, but it still had its detractors. Then, in 1923, the League of Nations – established in the wake of the First World War – held a special Committee of Enquiry Into the Reform of the Calendar, which took the 13-month system seriously.

The Committee wanted to find a standardized system and the neatness of the 13-month calendar seemed quite appealing. They named this plan the International Fixed Calendar or IFC. This arrangement would have meant that every month started on a Sunday and ended on a Saturday. It would make knowing which day a specific date fell on a lot easier (you’d never wonder which day payday was either).

Unlucky number 13

The hope was that this new calendar, a rather secular calendar devoid of religious days, would bring people together. However, it failed. Despite being popular among many prominent businessmen, including George Eastman – the founder of Kodak – from whom it gained its nickname, many were not happy.

Among the more resistant critics were many members of the international Jewish community, who feared the “blank” days that accompanied the new plan would fall on Saturdays, the Sabbath. In America, people were not happy that the planned 13th month would replace July and therefore interfere with Fourth of July celebrations. In practical terms, it was also feared that every form of monthly or quarterly rate and any contracts that relied on the Gregorian calendar would need to be renegotiated. Plus, the fact that 13 could not be divided without fractions would cause all sorts of issues.


In the end, the push for the 13-month calendar eventually lost momentum in the 1930s, right when it looked like it would succeed.

Correction: An earlier version of this article incorrectly stated the Sabbath as Sunday. It has been corrected to Saturday. 


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