Why throw away a perfectly good calendar? A website that lets you calculate when you can use it again.
🗓️
@polychrome
FYI: Neglecting moon phases and similar things, there are only 14 different calendars:
Seven calendars can be distinguished by their first (and last) week day of the year. Add to that the same seven calendars, but each having a different last week day, due to being a leap year.
Then it's just a matter of finding out what year maps to which calendar.
@floppy calendar trivia 🗓️ 
@polychrome
Great! I used to tediously calculate that myself with weird spreadsheets. That makes it much easier.