Killer Sudoku

Killer Sudoku reached newspaper fame when The Times introduced it on August 31, 2005. It keeps normal Sudoku rules, then adds dotted cages with sum totals. A cage marked 15 might hold two cells, three cells, or more, and the digits inside must add to 15. That makes the puzzle part placement logic and part combination logic. The challenge is choosing the only digit set that fits both the cage and the grid. Start with small cages and known combinations.

1. Fill the 9x9 grid with digits 1 through 9.
2. Keep every row, column, and 3x3 box free of repeated digits.
3. Read each dotted cage total.
4. Fill cage cells so their digits add to the total.
5. Use candidate notes for both Sudoku positions and cage combinations.
6. Finish when all Sudoku rules and all cage sums are satisfied.

• Standard Sudoku row, column, and box rules apply.
• Each cage must add to its printed total.
• Most Killer Sudoku puzzles do not repeat digits inside a cage, unless the rules state otherwise.
• Cages can cross 3x3 box boundaries.
• Given digits may be absent because cage totals provide clues.
• A valid puzzle has one solution.

• Memorize small combinations. Two cells summing to 3 must be 1 and 2; two cells summing to 17 must be 8 and 9.
• Use the 45 rule. Every row, column, and 3x3 box sums to 45.
• Look for cages fully inside one region. Their totals subtract from 45 to reveal missing cells.
• Use cage shape. A two-cell cage in the same row cannot repeat a digit because Sudoku already forbids it.
• Combine candidates with arithmetic. A cell may fit the cage total but fail in its row or box.

• Sudoku: The base number-placement puzzle without cage sums.
• Calcudoku: Uses arithmetic cages on smaller Latin-square grids.
• Kakuro: Uses sum clues in crossword-style runs.

• Cage sums create more starting points than hard Sudoku often gives.
• The 45 rule feels powerful once learned.
• Arithmetic combinations make each puzzle feel different.
• It rewards both Sudoku skill and number sense.

Play Killer Sudoku online for free. Use cage combinations, the 45 rule, and standard Sudoku logic to solve each grid without guessing.

Killer Sudoku adds cage arithmetic to familiar Sudoku logic. Start with fixed combinations, use the 45 rule, and let the grid narrow itself.

• The Guardian on The Times Killer Sudoku Launch
• Killer Sudoku Rules