Killer Sudoku - Play Free Online

Killer Sudoku (also known as Sum Sudoku) combines the logic of classic Sudoku with arithmetic. First published in The Times (London) in 2005, it quickly became one of the most popular Sudoku variants worldwide. Instead of pre-filled numbers, the grid is divided into groups of cells called "cages," each with a target sum displayed in the corner. Your goal is to fill every cell with digits 1–9 so that each row, column, and 3×3 box contains every digit exactly once - and every cage's digits add up to its target sum.

Because there are no given digits, Killer Sudoku relies entirely on cage-sum logic and elimination. It's a rewarding step up from regular Sudoku that trains arithmetic fluency, logical deduction, and pattern recognition.

Start by looking for cages with only one possible combination. For example, a 2-cell cage with sum 3 can only be {1,2}, and a 2-cell cage with sum 17 can only be {8,9}. Fill in any digits you can determine immediately.

Next, use the 45 Rule: each row, column, and 3×3 box must sum to 45. If a cage lies entirely within one row/column/box, you can calculate missing values by subtracting known cage sums from 45.

As you progress, combine cage combination logic with standard Sudoku elimination - checking which digits remain possible in each row, column, and box. Use pencil notes to track candidates, and gradually narrow down each cell to a single digit.

Regular Sudoku provides pre-filled given digits and requires pure placement logic. Killer Sudoku replaces givens with cage sums, adding an arithmetic layer. You must reason about which digits can add up to each target sum while simultaneously satisfying row, column, and box uniqueness.

Many players find Killer Sudoku more challenging because it requires tracking both digit possibilities and sum constraints. However, the cage-sum information also provides extra clues that standard Sudoku doesn't have - making it a different but equally satisfying logical puzzle.