What is Killer Sudoku?
Killer Sudoku is the most popular Sudoku variant in the world. It keeps every classic rule and adds cages: groups of cells outlined with a dashed line, each with a small number in its corner. The digits inside a cage must add up to that number, and no digit can repeat inside a cage.
Because the sums carry so much information, a Killer puzzle can start with very few numbers on the board — the challenge comes from combining arithmetic with logic. Every puzzle here has exactly one solution.
Rules
- Each row, column and 3×3 box contains the digits 1 to 9 exactly once.
- The digits in each dashed cage add up to the number in the cage's corner.
- A digit cannot appear twice in the same cage.
Killer Sudoku strategy
- Learn the unique combinations: a 2-cell cage of 3 must be 1+2, a 2-cell cage of 17 must be 8+9, and a 3-cell cage of 6 must be 1+2+3.
- Use the rule of 45: every row, column and box adds up to 45. If cages cover a box except for one cell, that cell is 45 minus the cages' total.
- Pencil in the possible digits for small cages first — they narrow down quickly.
- Look for cages that sit entirely inside one row or box; they remove their digits from the rest of that unit.
New to Sudoku logic? Start with our guide to playing Sudoku and the tips and strategy page — every classic technique works in this variant too.
Frequently asked questions
What is the difference between Killer Sudoku and normal Sudoku?
Killer Sudoku adds cages — dashed groups of cells with a target sum. You still fill every row, column and box with 1–9, but the cage sums give you extra clues, so the puzzle starts with fewer numbers.
Can numbers repeat in a Killer Sudoku cage?
No. Each digit can appear at most once in a cage, just as in a row, column or box.
What is the rule of 45?
Every row, column and box contains 1 to 9 once, so its digits always add up to 45. Subtracting the cage sums you know from 45 often reveals a single cell.
Is Killer Sudoku harder than regular Sudoku?
It feels different rather than simply harder. Our Easy level gives you more starting numbers and small cages; Hard has larger cages and very few givens.