Killer Sudoku

How to play Killer Sudoku

Killer Sudoku mixes Sudoku with simple sums. The board is a normal 9×9 grid split into nine 3×3 boxes, but it starts empty. Instead of given numbers, groups of squares are framed by dashed lines. Each group is called a cage, and the small number in its corner is the cage's sum.

Goal

Fill every square with a number from 1 to 9 so that:

• each row, column and 3×3 box holds 1 to 9 exactly once, as in classic Sudoku;
• the numbers in each cage add up to the sum in its corner;
• no number repeats inside a cage.

Every puzzle here is checked by a solver and has exactly one answer.

Step by step

1. Tap a square or move with the arrow keys. Its whole cage lights up, and the line under the grid shows the cage sum and how much is still missing.
2. Enter a number with the pad or the keys 1 to 9. Tap the same number again to clear it.
3. Turn on Notes (or press N) to pencil in small candidates. Placing a number removes that note from its row, column, box and cage.
4. Clashes turn red. A cage sum turns red when the cage is over its total, or full with the wrong total.
5. Use Erase, Backspace or Undo (Ctrl+Z) to fix mistakes.

Levels

Easy uses small cages of one to three squares, so many numbers are found quickly. Medium has bigger cages and almost no single squares. Hard uses the largest cages, where you must combine sums with Sudoku logic.

End of the game

The puzzle is solved when every square is correct. The timer stops and shows your time. Your game is saved in this browser, so you can return later. New to the rules? Warm up with classic Sudoku first.

Strategy tips

• Learn the fixed sums. Two squares adding to 3 must be 1 and 2; to 17, 8 and 9. Three squares adding to 6 are always 1, 2 and 3; to 24, always 7, 8 and 9.
• Use the 45 rule. Every row, column and box adds up to 45. Add the cages that sit fully inside a box, take that from 45, and you know the total of the squares left over.
• Start with single squares and tight cages. A one-square cage is a free number. Small or very large sums have only a few ways to be made.
• Note cage combinations. For a cage of 10 in two squares, the pairs are 1+9, 2+8, 3+7 and 4+6. Cross out pairs that clash with the row or box.
• Watch what is missing. The line under the grid shows how much the selected cage still needs. The last square of a cage is often easy.
• Mix in Sudoku logic. Once a few numbers are in, the usual row, column and box scanning does the rest.