Killer Sudoku — Classic Rules Plus Cage Sums

Killer Sudoku is classic Sudoku with arithmetic clues. The board above uses the same 9x9 grid, plus dashed cages that each show a sum. You can play killer sudoku online free, and your game saves automatically.

The cage rule

Keep the classic rules: every row, column and 3x3 box holds 1 to 9 once. Then add one more. The digits inside a cage must add up to the small number in its corner, and a digit cannot repeat inside a cage, even when the cage bends across two boxes. Many sums can be made in only one way. A two-cell cage of 17, for example, must be 8 and 9.

10

Possible combinations: 4

• 127
• 136
• 145
• 235

Why killers have few or no givens

Cage sums carry the clues that given digits carry in classic Sudoku. Easy Killer puzzles can start with a few placed digits. At Expert, Master and Legendary there are none at all: the cages alone fix the whole solution. The six levels use the same rating bands as the other modes, set by the hardest step a puzzle needs.

The 45 rule

Every row, column and box adds up to 45. When some cages sit completely inside one of them, subtract their sums from 45 to find what the remaining cells must total. Every cell belongs to exactly one cage, so all the cage sums on a board add up to 405. This is usually the first deduction on a fresh board, and it leads to innies and outies.

Cage techniques

Besides the classic patterns, Killer has its own techniques: cage combinations, innies and outies, captured candidates, cage splitting, cage and unit overlap, the rule of parity and cage compare. Keep the combinations chart close, because knowing which digits a sum allows is the quickest way in.

Where to learn

The Killer Sudoku rules walk through a full example board and your first moves. To see Killer next to other arithmetic puzzles, read the math sudoku variants overview. Ready for a no-givens challenge? Try Expert Killer.