How to Play Killer Sudoku

Killer Sudoku combines standard Sudoku with arithmetic cage clues. The grid is divided into cages — groups of cells outlined by dashed borders — each with a small number in the corner. The digits in each cage must sum to that number, and no digit may repeat within a cage. Standard Sudoku rules also apply throughout.

Every row, column, and 3×3 box contains the digits 1–9, which sum to 45. If you know the total of cages that sit entirely within a unit, you can deduce the sum of any partial cage cells crossing the boundary. These leftover cells are called 'innies' (inside the unit) or 'outies' (outside), and they often resolve to a single digit immediately.

Yes — Killer Sudoku typically has no pre-filled digits. All information comes from cage sums and Sudoku rules. Start with cages that have only one possible combination: a 2-cell cage summing to 3 can only be {1,2}, and a 2-cell cage summing to 17 can only be {8,9}. Apply the 45 Rule to each unit to find more placements.

In Killer Sudoku, digits within a cage must sum to the clue and cannot repeat within the cage. In Arrow Sudoku, digits along an arrow sum to the circle and can repeat. Killer cages are irregular shapes scattered across the grid; arrow cells follow a linear path from a circle.

Most players find Killer Sudoku harder than classic Sudoku at equivalent difficulty labels. Easy Killer puzzles are comparable to hard classic Sudoku. The arithmetic layer adds complexity, but cage constraints also provide more starting information than simple given digits once you learn to exploit them fully.

Easy puzzles take 10–20 minutes. Medium puzzles run 20–40 minutes. Hard puzzles average 40–75 minutes and expert puzzles often exceed 90 minutes. Applying the 45 Rule fluently is the single biggest factor in improving solve speed.