Year code (odd + 11)

The whole odd+11 route: turn a year into the 0–6 code you add to the century anchor

Experimental

The Year code (odd + 11) drill is new and still finding its feet. Nothing about it is locked in — it may change shape, or go away again, depending on what people make of it. If you have an opinion, tell me.

Level selection

How to play— show the rules

The whole odd + 11 route, end to end. Given a year, work out the 0–6 code you would add to the century anchor to get that year’s doomsday.

Last two digits. Odd? Add 11.
Halve it.
Odd? Add 11.
Take what’s left from 7: 7 − (n mod 7).

Watch the last step — reaching for n mod 7 and forgetting to subtract it from 7 is the single most common slip on this route, and it quietly gives you the wrong weekday every time.

Year	Odd? +11	Halve	Odd? +11	7 − mod 7
1966 (66)	66	33	44	5
1985 (85)	96	48	48	1
2024 (24)	24	12	12	2
1999 (99)	110	55	66	4

This is the odd+11 counterpart of the sum modulo 12 and divisor of 4 drill — same answer, different road to it.