What is Killer Sudoku?

Killer Sudoku combines the logic of classic 9×9 Sudoku with arithmetic cage constraints. The grid is divided into "cages" — groups of cells outlined with dotted borders. Each cage shows a small target sum in its corner. Your goal: fill every cell with digits 1–9 so that no digit repeats in any row, column, or 3×3 box, and the digits within each cage add up exactly to the cage's target. Unlike regular Sudoku, no digit may repeat inside a cage either.

How to Play Killer Sudoku

• Identify forced cages

  Small cages with unique sums have only one possible combination — a 2-cell cage summing to 3 must be '{'1, 2'}'; a 2-cell cage summing to 17 must be '{'8, 9'}'. Start there.

• Apply standard Sudoku rules

  Every row, column, and 3×3 box must contain digits 1–9 without repetition. Use these constraints alongside cage sums to eliminate candidates.

• Use cage combinations

  List all possible digit combinations for each cage. Overlapping logic between cages and rows/columns will narrow down candidates quickly.

• Fill in what you know

  As cells resolve, update remaining cages. Even a single confirmed digit can unlock a chain of deductions across the grid.

Tips & Tricks

• The 45 Rule

  The digits 1–9 always sum to 45. Any complete row, column, or 3×3 box sums to 45. Use this to calculate "innies" and "outies" — cells that stick into or out of a cage region.

• Spot Unique Combinations

  Some cage sums can only be achieved one way. A 3-cell cage summing to 6 must be '{'1, 2, 3'}'. Memorising key combinations speeds up solving.

• No Repeats Inside Cages

  Unlike rows and columns, a cage's no-repeat rule applies to the cage itself regardless of size. Use this as an extra elimination layer on top of standard Sudoku constraints.

• Start with the Most Constrained Cages

  Small cages (2–3 cells) with extreme sums (very low or very high) have the fewest possible combinations. Solve these first to anchor the rest of the grid.