Overview
Killer Sudoku combines standard Sudoku rules with outlined cages. Digits inside each cage must add to the printed cage total, usually without repeating within that cage.
Objective
Complete the Sudoku while also making every cage equal its target sum.
What You Need
- A Killer Sudoku puzzle
- Pencil or candidate notes
- Knowledge of standard Sudoku rules
Setup
Apply the normal row, column and box rules first. Then inspect each cage total and size to determine which digit combinations are possible.
How to Solve
- List possible combinations for small cages.
- Remove combinations that conflict with row, column or box digits.
- Use fixed or nearly fixed cages to place digits.
- Apply standard Sudoku singles and candidate techniques.
- Use completed cage sums to find remaining values.
- Continue alternating between cage arithmetic and Sudoku logic.
Worked Example
A two-cell cage totalling 3 can only contain 1 and 2. If one cell cannot be 1 because its column already contains 1, that cell must be 2 and the other must be 1.
Strategy Tips
- Memorise common two-cell combinations for small and large totals.
- Use the 45 rule: digits 1–9 total 45 in every complete row, column and 3×3 box.
- Treat cage possibilities as sets until position information fixes their order.
Common Mistakes
- Repeating a digit inside a cage when the puzzle forbids it.
- Using the cage sum but forgetting ordinary Sudoku constraints.
- Assuming a combination’s digits have fixed positions too early.
Variations & House Rules
Some Killer Sudoku variants allow repeated cage digits or add diagonal and other constraints. Always check the puzzle’s stated rules.
FAQ
Why does 45 matter?
The digits 1 through 9 add to 45, so every completed standard Sudoku row, column and box totals 45.
Is Killer Sudoku harder than standard Sudoku?
It can be, but cage totals also provide extra information that sometimes creates very direct deductions.