What is this?

The International Fixed Calendar is an alternative to the Gregorian Calendar that we all know and love (hate? hate.) It was proposed by Moses Cotsworth in 1902. He created the International Fixed Calendar to solve common problems caused by the traditional Gregorian Calendar:

• Months in the Gregorian Calendar can have different numbers of days. Some hourly workers get screwed by this every February, because they get paid for significantly fewer working hours than they do in other months while bills like rent stay the same.
• The same dates in different months and years fall on different week days. Ever tried to figure out the week day of your birth date? It's very easy to do with the International Fixed Calendar.
• From year to year, holidays can fall on different week days, and sometimes on wildly different dates (Easter, for example). This causes a lot of problems for businesses that can't easily shut down for a day and quickly start up again after the holiday (think big factories - some of these can take days to shut down and start up again).

How does it work?

The International Fixed Calendar uses the same year numbering and number of weekdays as the Gregorian Calendar. However, the calendar is divided into 13 months with 28 days, giving each month exactly 4 weeks. The thirteenth month, Sol, is between June and July. Every year and month begins on a Sunday, so the same date in each month or year will always be on the same week day as well.

International Fixed Calendar Leap Years work similarly to Gregorian Leap Years: every 4th year, except in years that are divisible by 100 but not divisible by 400. The leap day is added to June instead of February. The extra day has no week day name (e.g., "Sunday" or "Monday") but is instead called "Leap Day". It happens between the last Saturday of June and first Sunday of Sol.

If you're doing the math, you probably noticed that 13 months x 28 days = 364 days per year. Where is the extra day? The extra day is added to the end of December. Like Leap Day, December 29th has no named week day but is called "Year Day" instead.

Learn More

• The Eastman Kodak Company used the International Fixed Calendar from 1928 to 1989. The company's founder, George Eastman, was an outspoken proponent of the International Fixed Calendar. You can read his defense of the International Fixed Calendar here.
• I first heard about the International Fixed Calendar on the 99% Invisible podcast. Listen to the episode here.
• The Wikipedia article on the International Fixed Calendar lists the advantages and disadvantages of the International Fixed Calendar.