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The Monotonic Calendar has a 365-day year, which means week days predictably shift by one day every year. If you print every year calendar there would be seven versions, one for each day of the week. For example when the year starts on Sunday, it will also end on Sunday and the next year will start on Monday.

The months are the same as the Gregorian calendar except that February has a fixed 28 days length and the 29 February date is abolished.

Good Resolutions Week[]

Every 29 years, seven intercalary days are added at the end of the year. Although they technically belong to the year they are added to, you should think of these seven days as preparation for the new year to come. So if the next year is X, you can call them "seventh day to X", "sixth day to X", "fifth day to X", "fourth day to X", "third day to X", "second day to X" and New Year's Eve.

Computer systems can just consider the intercalary days as a short seven-day thirteenth month and count the days up in the same way as other months.

To reflect that these days prepare for the year ahead, they are named after New Year's Resolutions. The Good Resolutions Week (GRoW for short) is a time to think of what you wish of yourself in the new year. The GRoW can actually start with any day of the week, but it is called like that because it lasts seven days. The monotonicity of the calendar is preserved when a GRoW is added to the year.

Year Length Cycle[]

When a Good Resolutions Week is added the year length changes to 372 days. That generally happens every 29 years but it can occasionally be 28 years instead. The mean year length using purely a 29-year cycle is 365.24138 which is slightly short.

To determine the next "long" year after year Y use the following formula:

X = Y0 + Round(RoundUp((Y-Y0)*(l-365)/7) * 7 / (l-365))


l is the agreed-upon mean length of the tropical year (suggested: 365.2421904)

Y0 is the agreed-upon epoch year of the cycle

In the formula, only l is a non-integral number so the calculation can (should) be done with fixed point numbers. Binary scaling should be used for consistent and efficient calculations.

To keep the dates closer to the Gregorian calendar, it is recommended to set the start of the leap cycle three or four days before the Gregorian date. For example, 1 January in the Monotonic calendar could be 29 December in the Gregorian calendar at the beginning of the cycle.