Killer Sudoku
Killer Sudoku takes the 1–9 grid you know and adds dashed “cages” that must add up to a target sum — and no digit may repeat inside a cage. It’s Sudoku crossed with the cross-sums of Kakuro: pure logic, no arithmetic luck, one solution every time. Play a board below, then read the rules and strategy underneath.
How to play Killer Sudoku
- Fill the grid — every row, every column and every 3×3 box must contain the digits 1–9 exactly once, just like classic Sudoku.
- Add up the cages — each dashed-outline group must total the small number printed in its top-left corner.
- No repeats in a cage — a digit can appear at most once inside any single cage (on top of the usual row, column and box rule).
- Use the sums as clues — on a pure killer board there are no starting digits; the cage totals are your way in. (Easy boards reveal a few digits to get you started.)
- Play it — tap a cell then a number to fill it, ⌫ to clear. Every puzzle is solvable by logic alone and has exactly one answer.
What is Killer Sudoku?
Killer Sudoku (also written “killer sudoku” or sometimes “sumdoku” / “addoku”) is a Sudoku variant that swaps starting digits for cages with sums. You still place 1–9 in every row, column and 3×3 box, but the grid is divided into dashed groups — cages — and the digits in each cage must add up to the number shown in its corner, without repeating.
Because a pure killer board usually starts with no given numbers at all, the whole puzzle is driven by those sums. It’s a favourite of solvers who like Kakuro’s cross-sums and classic Sudoku equally.
How the cages work
Each cage is the dashed outline with a little number in the corner; that number is the sum of every digit inside the cage. Two rules combine: the digits in a cage must add to its total, and — like a mini row — they can’t repeat. So a two-cell cage summing to 3 can only be {1, 2}; one summing to 17 can only be {8, 9}. These forced “cage combinations” are the heart of killer solving.
Killer Sudoku strategy
Start with the most constrained cages. Small cages with extreme sums have only one possible set of digits — a 3-in-two cage is {1,2}, a 4-in-two is {1,3}, a 16-in-two is {7,9}. Pencil those in first.
Use the rule of 45. Every row, column and 3×3 box holds 1–9, so it sums to exactly 45. If the cages inside a box almost fill it, the leftover cell (an “innie”) or the bit poking out (an “outie”) is forced by simple subtraction. Combine the 45 rule with normal Sudoku scanning and most boards fall.
Easy and hard killer boards
Easy killer boards here use mostly small two-cell cages plus a handful of starting digits, so there’s always a tight clue to work from. Hard boards use larger cages with more possible combinations and far fewer hints, so you lean on cage combinations and the 45 rule. Tap New for an endless supply, or switch level with the buttons above the grid.
Killer Sudoku: FAQ
What’s the difference between Sudoku and Killer Sudoku?
Classic Sudoku gives you some starting digits; Killer Sudoku gives you cages with target sums instead. You still fill 1–9 in every row, column and box, but the digits in each dashed cage must add up to its number and can’t repeat.
Can a number repeat inside a killer cage?
No. A digit can appear at most once in any cage, in addition to the usual rule that it can’t repeat in a row, column or 3×3 box.
What does the small number in the corner mean?
It’s the sum of all the digits in that cage. For example, a two-cell cage marked 4 must contain digits that add to 4 with no repeat — so {1, 3}.
Do I need to be good at maths?
Not really — the only arithmetic is small additions up to 45. Killer Sudoku is a logic puzzle: every board has exactly one solution reachable by reasoning, never by guessing.
Is Killer Sudoku free to play here?
Yes — it plays free in your browser on phone, tablet and desktop, with no download and no sign-up. Tap New for a fresh board any time.