The Forgotten Campaign to Create a 13-Month Calendar

Why do some months have 30 days, others 31, and then one only has 28 (or 29 come leap year)? It just doesn't make sense. Or so thought the man who reinvented the annual calendar to have 13 months. Why didn't it catch on?

Monthly Review

Around the turn of the 20th century, Moses B. Cotsworth, an accountant for the British Railway, was running into issues with the calendar. In a perfect world, he'd be able to compare the railway company's revenue from one month to the next and immediately recognize how things were going. But he couldn't. For one thing, months varied between lengths of 28, 29, 30, and 31 days. For another thing, every weekday appeared in a different quantity from month to month — a troubling problem for a company that knew Mondays would always account for 18 percent of their average weekly revenue while Sundays would only rake in 4 percent. So if the railway made less money this month than it did last month, was it because it had fewer customers this month? Or was it because this month had fewer days, or fewer Mondays, or more Sundays? It was a frustrating problem, to say the least.

The 13-month, or Cotsworth, calendar

So instead of struggling, Cotsworth invented a new calendar. In Cotsworth's design, there are 13 months of exactly 28 days. Every month has four weeks, and every date has a dedicated weekday. The 1st is always a Sunday; the 13th, interestingly, is always a Friday. Cotsworth's 13th month is called Sol, for the summer solstice, and lands between June and July when the solstice occurs. The leap day was also reassigned from its previous role in February to a place at the end of Sol. To round out 365 days, Cotsworth added Year Day after the 28th of December as a global holiday that belonged to no individual month.

Related Video: Why Does February Have 28 Days?

Who Caught On?

It may surprise you to learn that Cotsworth's calendar was wildly popular at the time — among businessmen, at least. It was especially persuasive to one prominent businessman: the founder of Kodak, George Eastman. Eastman spent his own money to promote the new calendar to the masses, converting some of the U.S.'s most prominent businessmen in the process. He also put his money where his mouth was: Kodak implemented the 13-month calendar in 1924, and it stayed in place organizing the company's finances and production all the way until 1989.

Entrepreneur George Eastman adopted the 13-month calendar at Eastman Kodak Company from 1928 to 1989.

But while businesses might welcome the predictability of a 13-month calendar, everyday Americans did not. The biggest problem may have been the destruction of Independence Day, also known as the 4th of July. The calendar's approach to holidays was to place them on the Monday closest to their original date to allow for a three-day weekend. When it came to Independence Day, the adopters had two options: They could either keep it in July but place it on a Monday, which would make it the 2nd of July, or keep it where it is in the year, which would make it the 16th of Sol. Both of those options were nonstarters.

The public never had enough of a reason to switch to Cotsworth's calendar, and with Kodak's eventual reversal to a 12-month system, the idea died out. But that doesn't make it a bad idea — it just seems that sometimes, the fix for a problem is more effort than it's worth.

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Learn more about the history of the calendar in "Calendar: Humanity's Epic Struggle to Determine a True and Accurate Year" by David Ewing Duncan. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer April 19, 2019

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