Calcudoku 2026-10-16
The clock starts when you hit Start — server-timed.
You're not signed in — play free, unofficial and untimed-on-the-board. Your time shows at the end with the rank it would have earned. Sign in first to make it count.
How to play calcudoku
- The grid rule: every row and every column holds each number from 1 to the grid size exactly once. Like sudoku, but with no boxes.
- The cages: the heavy outlines split the grid into cages. Each cage has a small target in its top-left corner —
12×,7+,3−,2÷. The numbers you put in that cage must make that target with that operator, in any order. - A cage showing a bare number is a freebie — it’s already filled in for you.
- − and ÷ cages are always two squares, and they mean larger-minus-smaller / larger-divided-by-smaller. Cages of three or more are only + or ×.
- Numbers may repeat inside a cage — the no-repeats rule applies to rows and columns, not cages. This is the bit that trips everyone up.
- Click a cell, then type a digit or tap the number pad. ⌫ erases. It checks itself when the grid is full.
How to play calcudoku
- The grid rule: every row and every column holds each number from 1 to the grid size exactly once. Like sudoku, but with no boxes.
- The cages: the heavy outlines split the grid into cages. Each cage has a small target in its top-left corner —
12×,7+,3−,2÷. The numbers you put in that cage must make that target with that operator, in any order. - A cage showing a bare number is a freebie — it’s already filled in for you.
- − and ÷ cages are always two squares, and they mean larger-minus-smaller / larger-divided-by-smaller. Cages of three or more are only + or ×.
- Numbers may repeat inside a cage — the no-repeats rule applies to rows and columns, not cages. This is the bit that trips everyone up.
- Click a cell, then type a digit or tap the number pad. ⌫ erases. It checks itself when the grid is full.
Calcudoku: the thinking person’s number grid
Calcudoku — you may have met it as KenKen or MathDoku — is a latin square with arithmetic on top. Fill the grid so every row and every column holds each number exactly once, while the heavy-outlined cages hit their targets: 12× means the cage multiplies to twelve, 3− means the pair differs by three. There’s one 5×5 here every day, free, and it is quietly the most fought-over board on the site — it ruins lunch breaks precisely because it looks so harmless.
How to actually get good
Freebies first: single-cell cages are already answers. Then enumerate the small cages — a two-cell 2÷ on a 5×5 grid can only be 1-2 or 2-4, and writing that down is worth more than staring. Factor the big × cages next: a large multiplication target usually has one legal decomposition once you rule out repeats in its rows and columns. And keep the two rules that trip everyone pinned up: numbers may repeat inside a cage — rows and columns are the law, cages aren’t — and − / ÷ cages are always exactly two squares, larger against smaller. Arithmetic beats trial-and-error here, every single time.
Rated the hard way
The clock runs on the server from Start to the final digit, and a rated solve has to survive a full input replay plus human-pacing checks before the leaderboard shows it — the whole scheme is in how the honest board works.
Every past cage grid is in the calcudoku archive.