International Fixed Calendar Converter (Cotsworth)

Moses Cotsworth proposed a calendar of thirteen months of twenty-eight days each in 1902. That comes to 364, and the leftover day sits outside any month and any week — Year Day, at the end of the year. In a leap year a second loose day appears, Leap Day, in the middle of the year. The new month is called Sol and goes between June and July, near the solstice.

The advantage is that every month becomes identical: exactly four weeks, always starting on Sunday and ending on Saturday. The 1st is always a Sunday, the 13th always a Friday — hence the joke that a fixed calendar delivers Friday the 13th thirteen times a year. For accounting and payroll it solves a real irritation: months comparable to one another, with no correction for working days.

Eastman Kodak adopted the calendar internally in 1928, at George Eastman's insistence, and only dropped it in 1989 — long after the League of Nations had studied and shelved the proposal in the 1920s. Two objections sank it: thirteen is prime and will not divide into quarters, and the loose days interrupt the seven-day cycle, which religious groups rejected for breaking the count of the sabbath.