How to play Killer Sudoku

The goal

Cages

• Each dashed outline is a cage. The small number in its top-left corner is what its squares add up to.
• A number can’t repeat inside a cage, so a cage of 2 squares adding to 4 must be 1 and 3, never 2 and 2.
• Most puzzles start with an empty grid: the sums are your clues.

Playing

• Tap a square, then tap a number to place it. Tapping the same number again clears the square.
• The selected square’s row, column, box and cage are shaded, and its cage outline is highlighted.
• Under the board, the cage helper shows the selected cage’s sum, how much is left to place, and the sets of numbers that could make it. Tap the eye to hide or show the sets.
• Each number key shows how many of that number are still to place.

Tools

• Notes: turn it on to pencil in possible numbers. Placing a number removes it from the notes in the same row, column, box and cage.
• Erase clears the selected square. Hint fills in the selected square, or the next one that needs it. Undo takes back your last change.
• A number that repeats in a row, column, box or cage turns red, and a cage sum turns red if its numbers add up to too much or don’t match when the cage is full.

Tips

• Every row, column and box adds up to 45. If the cages inside a box cover all but one square, that square is 45 minus their sums. The same works across two or three rows.
• Small and large sums have few combinations: 3 in two squares is always 1+2, and 17 is always 8+9.

Difficulty

• Easy: small cages and a few numbers to start.
• Normal: an empty grid with cages of up to 4 squares.
• Hard: bigger cages, up to 5 squares.
• Expert: the biggest cages. You’ll usually need the 45 rule across several rows or columns.
• Every puzzle is new and can be solved by logic alone, with exactly one solution. Your best times are kept for each difficulty.

Keyboard

• 1–9 to place a number, the arrow keys to move, Backspace to erase, N for notes, H for a hint, and Ctrl or ⌘+Z to undo.

Questions

Strategy guides