10 points
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Have a “liminal day” that serves as New Year’s Day, and then every leap year put the extra day as the last day of the leap year after the last month.
The big trouble is that there isn’t a subdivision between the month and the year, 13 is prime, there isn’t a whole number division of months that can be used to mark say a fiscal quarter for example.
So I say instead of a 13th month, split those 4 weeks to be an extra week at the end of every 3rd month, so March, June, September, and December would all have 35 days instead of 28.
Kinda what Caesar was going for originally too, having the months alternate between 30 and 31 days, but he fucked it up because Romans were superstitious about February for whatever reason.
