Killer Sudoku: rules, combinations & how to solve

What is Killer Sudoku?

Killer Sudoku is Sudoku with arithmetic. The usual rules apply (each row, column and 3×3 box holds 1–9 once), and the grid is also divided into dashed-outline cages. Each cage has a small number in its corner, and the digits in that cage must add up to it. A digit cannot repeat inside a cage.

Most Killer puzzles start with few or no given digits, because the cage sums do the work. Every Sudokumee Killer puzzle is checked to have exactly one solution.

Cage combinations that have only one answer

These cages can only be made one way, so you can fill the digits in as candidates immediately. Memorise them and Killer gets much faster.

How to solve Killer Sudoku

1. Start with cages that have a single possible digit set (table above).
2. Apply the 45 rule to rows, columns and boxes to find single cells.
3. Where a cage has two possible sets, note the digits they share. Those digits must be in the cage.
4. Use normal Sudoku logic: singles, pairs and the techniques in our Sudoku tips guide.
5. Sudokumee shows the valid combinations for the cage you select, so you can check your reasoning as you go.

4-cell cage combinations

Each set of digits that adds up to the cage sum.

Try it

Ready to practise? Play a free Killer puzzle with the live cage-sum helper, or read the rules for Diagonal Sudoku and the other Sudoku modes.