Killer Sudoku

Killer Sudoku. Cages sum to the small number in their corner. Digits cannot repeat within a cage.

How to play

Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1 to 9 with no repeats — the classic Sudoku rule. Killer Sudoku adds one twist: Cages sum to the small number in their corner. Digits cannot repeat within a cage.

Killer sudoku layers arithmetic onto the classic grid: the puzzle is carved into dotted-outline regions called cages, and the small number printed in each cage's corner is the sum its digits must add up to. No digit may repeat inside a cage, and — unlike ordinary sudoku — a killer grid usually begins with no given numbers at all, so every clue you get comes from the cage sums. That makes each solve a blend of logic and light mental arithmetic rather than pure pattern-spotting.

How to solve Killer Sudoku

Begin with the cages that have the fewest possible digit combinations — the small and large sum extremes. A 2-cell cage summing to 3 can only be {1,2}, a 3-cell cage summing to 7 can only be {1,2,4}, and a 3-cell cage summing to 24 can only be {7,8,9}; pencil those forced sets in first. The no-repeat rule trims the middling sums too — a 2-cell cage summing to 10 can't be {5,5}, so it is one of {1,9}, {2,8}, {3,7} or {4,6}. Then lean on the 45-rule: every row, column and box totals 45 (that's 1+2+…+9), so when cages fill all of a unit bar one square, that leftover square equals 45 minus the cage sums — and cages that spill just one cell in or out of a box (innies and outies) pin a value the same way. Finally, where a cage's candidate set overlaps a nearly-finished row or box, strike out any digit that unit has already placed to collapse the cage to a single option.

Every Killer Sudoku puzzle is free to play in your browser — no ads, no sign-up, and it works offline.

Frequently asked questions

What is Killer Sudoku?

Killer Sudoku is a variant that combines standard sudoku with simple sums. The grid is divided into dotted cages, and the digits inside each cage must add up to the small total shown in its corner without repeating. Because a killer puzzle typically has no starting numbers, you solve it by working out which digit combinations each cage sum allows and where they can legally sit.

What are the rules of Killer Sudoku?

The base rule still holds: each row, column and 3x3 box must contain the digits 1 to 9 exactly once. On top of that, the digits within each dotted cage must sum to the number in the cage's corner, and no digit may appear twice in the same cage. There are no other given clues — the cage sums are your only starting information.

What is the 45-rule in Killer Sudoku?

Since every row, column and box holds 1 to 9, each of those units always sums to 45. If cages cover an entire unit except one cell, that stray cell must equal 45 minus the total of those cage sums. The same trick handles innies and outies — a cage poking one cell into or out of a box — letting you deduce a value without knowing the rest of the cage.