Calendar reform - 13 equal months

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One of the many topics I’m unreasonably passionate about is the fact that our system for dividing time needs an overhaul; most urgently, the calendar. The Gregorian calendar is an inconsistent patchwork of historical leftovers: twelve months with uneven lengths, alternating long and short except for August and September. And of course February, the runt of the litter, limps along with 28 days - or 29, if the cosmos feels generous.

In 1902, Moses B. Cotsworth proposed a saner alternative: The International Fixed Calendar (IFC), with thirteen months, all with a clean and tidy 28 days. Simple arithmetic then gives you 364 days, so he placed the extra day outside the calendar entirely, naming it “Year Day.” Leap years add another standalone day, “Leap Day.” These intercalary days don’t belong to any week or month, which feels weird until you realise it makes everything else dramatically more predictable. Technically, yes, you could argue this makes fourteen “units,” but that’s besides the point.

In this system, every month looks the same, and every date always falls on the same weekday. The year always starts on a Monday. The 2nd, 9th, 16th, and 23rd will always be a Tuesday. No knuckle-counting required.

Changing the calendar raises a few practical concerns, especially around finances, because so much of our lives revolves around the twelve-month cycle. The knee-jerk reaction is something like “Do I get an extra paycheck?” or, conversely, “Do I owe my landlord more money?” Fortunately, the math stays fair. Your yearly income doesn’t change; it’s simply divided by thirteen instead of twelve. If you make $2,000 a month now (i.e., $24,000 per year), your new monthly payout becomes $24,000 ÷ 13 ≈ $1,846.15. Lower number, yes, but you now get it every 28 days instead of the current mess of 28/30/31.

Landlords and banks may instinctively rub their hands together and imagine sneaking in an extra payment, but no: annual totals remain the same. The only thing that changes is how you slice them.

Definitely worth mentioning is the fact that Kodak (yes, that Kodak) actually used this calendar internally from 1928 and all the way up to 1989! And if they could do it, then why not the rest of society?

Converting birthdays (and any other fixed dates) is where things get interesting. Everything is fine until January 28th. After that, the Gregorian and International Fixed calendars part ways. From day-of-year 29 onward, every date must be converted, because the neat 28-day structure no longer aligns with the Gregorian chaos. So yes, people born on the 29th, 30th, or 31st of any month will definitely notice the shift; but so will everyone else with a birthday past late January.
The method is simple: take your Gregorian date, convert it to its day-of-year number, and then map that number into the new structure. For example, June 20th is day 171 in a common year (172 in a leap year). In the IFC calendar, day 171 becomes Sol 3. It’s a noticeable jump, and perfectly reasonable if people need a moment to adjust.
In my case, with my birthday being December 31st, New Years Eve, and as we've already seen, that is now Year Day, which I am actually very happy about!

Public holidays raise similar questions. Take Norway’s Constitution Day. “Hurra for 17. mai” is practically hardwired into us. May 17th is day 137 (or 138), which converts to May 26th in the Cotsworth calendar. That’s… an adjustment. Alternatively, we could tie celebrations to their historical Gregorian dates instead. In that case, “May 17th” in IFC corresponds to May 9th Gregorian. So we have to decide: do we celebrate the date, or the position in the year? A fun little philosophical puzzle, depending on how attached you are to flag-waving.

The same questions arise for other public holidays - including Christmas, Liberation Day, and everything else culturally anchored to weird little quirks of the Gregorian system.

A curiosity worth mentioning: 2024 was a perfect demo-year for the IFC layout because the year started on a Monday in the Greg.cal too! This happens again in 2029, so we have three years (considering we are currently in November) to prepare for the change!

Resources:
Wikipedia: International Fixed Calendar (visited 26.12.2025)
Nature.com: Calendar Reform (visited 26.12.2025)
The Internet says it's true: 13 months: The Kodak Calendar Experiment (visited 26.12.2025)