Killer Sudoku (also known as Sumoku, Sum Doku, or Samunamupure) is a puzzle that combines elements of Sudoku and Kakuro. Despite the intimidating name, many players find it easier than regular Sudoku once they learn the basic arithmetic strategies.
The Rules
Killer Sudoku follows all the standard rules of regular Sudoku (1-9 in every row, column, and 3x3 box). However, it introduces one major twist:
- The grid is covered in dotted outlines called cages.
- Each cage contains a small number in the top-left corner.
- The numbers placed inside the cage must add up exactly to that target number.
- Numbers cannot repeat within a single cage.
The Rule of 45
The most important mathematical secret to Killer Sudoku is the "Rule of 45". Because every row, column, and 3x3 box must contain the digits 1 through 9 exactly once, the sum of any complete row, column, or box is always exactly 45 (1+2+3+4+5+6+7+8+9 = 45).
You can use this to your advantage. If a 3x3 box is entirely filled by cages, except for one single cell hanging outside the cages, you can calculate the exact value of that outside cell by adding up the cages and subtracting from 45!
Killer Sudoku Strategy: Cage Combinations
The fastest way to crack Killer Sudoku is to memorise a few "locked" cage combinations — sums that can only be made one way. A two-cell cage summing to 3 must be 1 and 2; a 4 must be 1 and 3; a two-cell 17 must be 8 and 9. Three-cell cages of 6 (1-2-3) and 24 (7-8-9) are equally rigid. These forced sets give you guaranteed candidates with zero guesswork. Combine them with the no-repeat rule inside each cage, then cross-reference the rows, columns, and boxes those digits touch to unlock the surrounding cells.
Killer Sudoku vs. Classic Sudoku
Killer Sudoku keeps every rule of classic Sudoku — 1 to 9 in each row, column, and 3x3 box — and layers arithmetic on top. Where a classic grid hands you several starting digits, a Killer grid usually starts completely empty; your first clues come from the dotted cages and their target sums. That makes the opening feel harder, but the cage maths often gives you more certain deductions than classic scanning once you spot a locked combination. If you enjoy mental arithmetic, Killer can actually feel friendlier than a hard classic puzzle despite its fearsome name.
More Sudoku to Play
Prefer shapes to sums? Try Jigsaw Sudoku, the irregular-region variant, or see every option on our Sudoku variants hub. You can also return to the classic Daily Sudoku puzzle.