Killer Sudoku strategy: how to read cages and eliminate combinations

Prioritize cages with few valid combinations

Killer Sudoku adds sum information to Classic Sudoku rules. Good starting points are often single-cell cages, two-cell cages with very low or high totals, or cages where row, column, or block rules already eliminate many digits.

You do not need to list every permutation. For a two-cell cage totaling 3, the only set is {1,2}; for 17, it is {8,9}. When a cage has multiple combinations, keep the feasible digit sets and use Sudoku positions to eliminate them gradually.

• Look for a single-cell cage or a two-cell cage with an extreme sum.
• Remember that digits cannot repeat within the same cage.
• Use Sudoku rules to eliminate digits before considering order within a cage.

Cages are not separate from rows, columns, and blocks

A combination can match the total but not the positions. If a cage needs {2,7} but the first cell's column already contains 2, that cell must be 7 and the other cell 2. This is why Killer Sudoku is not just arithmetic; Sudoku rules still determine most positions.

When several cells of a cage lie in the same block, check locked candidates and pairs. A cage digit set can sometimes create a natural hidden pair in a row/column and eliminate candidates outside the cage.

Calculate the missing total instead of solving every cage independently

Each row, column, and 3×3 block totals 45. When cages cover almost an entire region, the missing total can identify one cell or a group of cells faster than listing combinations for every cage. This is the basis of the Rule of 45 and innies/outies techniques.

Write the equation at the group-total level first, then compare it with candidates. If two cells must sum to 10, that does not identify either digit yet; Sudoku rules still need to filter {1,9}, {2,8}, {3,7}, and {4,6}.

What order should you learn Killer techniques in?

Master Classic Sudoku rules first, then learn 2–3 cell cage combinations, followed by the Rule of 45. Once comfortable, move to advanced techniques such as multi-region innies/outies. This learning order helps you understand why a sum matters instead of memorizing combination tables.

If a Killer game makes you keep trying numbers, lower the difficulty. The goal is to use sums to narrow candidates, then let Sudoku logic finish the move.