Killer Sudoku
Sudoku with sums instead of givens — for the confident solver.
How to play Killer Sudoku
Killer Sudoku keeps the two Sudoku rules — every row, column and 3×3 box holds 1–9 with no repeats — but instead of starting numbers, it gives you cages: dotted groups of cells with a small sum in the corner. The numbers in a cage must add up to that sum, and a number can't repeat inside a cage. From those sums alone, the whole grid can be deduced.
Tap a cell, then tap a number. Use Notes to pencil in candidates, Erase to clear, and Hint to fill the selected cell if you're stuck. Wrong numbers are highlighted so you can catch a slip early.
The one trick that unlocks it
Because each row, column and box contains 1–9, it sums to 45. That "rule of 45" is the heart of Killer Sudoku: if a box's cages add to, say, 40 and one cell pokes out of the box, that cell must be 45 − 40 = 5. Chaining these totals across boxes cracks open even hard grids.
Cage combinations worth memorising
- Two cells: a sum of 3 can only be 1+2; a sum of 17 only 8+9; a sum of 4 only 1+3.
- Three cells: 6 is only 1+2+3; 24 is only 7+8+9.
- These "locked" cages give you a firm foothold — find them first and let the row/column rules spread the certainty.
Why it's a step up from Sudoku
Regular Sudoku is pure placement logic. Killer Sudoku adds arithmetic on top: you're constantly totting up cages, subtracting from 45, and testing which digit combinations fit. It's the natural next puzzle if you find ordinary Sudoku a little too gentle and you enjoy a bit of mental addition with your deduction.
Frequently asked questions
Is Killer Sudoku free here?
Yes, completely free with no sign-up. It runs in your browser and your best time is saved on your device.
Can a number repeat inside a cage?
No. Within a single cage every number must be different, in addition to the usual Sudoku rule of no repeats in a row, column or box.
What is the "rule of 45"?
Every row, column and 3×3 box contains the digits 1–9, which always add up to 45. Comparing that fixed total to the cage sums lets you deduce the value of cells that stick out of a region.
Does each puzzle have one solution?
Yes. Every board is generated and verified to have exactly one solution, solvable from the cage sums by logic alone.
Why does a puzzle take a moment to appear?
Each Killer Sudoku is generated fresh and checked for a unique solution before you see it, which takes a fraction of a second.