I really like the “2053” pattern, it's easy to remember. But I doubt I will be able to remember the rest. I think I'd rather do like this: Given a year CCXX, w

I really like the “2053” pattern, it's easy to remember. But I doubt I will be able to remember the rest. I think I'd rather do like this: Given a year CCXX, we know the doomsday of year CC00 from the “2053“ rule, and then: (a, b) = divmod(XX, 12) c = b // 4 offset = a + b + c Then add the offset to the day found by the “2053” rule, and you have the doomsday of the year. E.g., for 2020 we have: start = 2 # from the 2053 rule (a, b) = divmod(20, 12) # (1, 8) c = 8 // 4 # 2 offset = 1 + 8 + 2 = 4 (mod 7) doomsday = 2 + 4 = 6 # saturday