Killer Sudoku online free: three daily puzzles, easy to hard

Killer Sudoku is sudoku played with sums. The rules are the same: every row, every column and each of the nine 3×3 boxes holds the digits 1–9 exactly once. The difference is that hardly any digits are given. Instead you see cages, groups of cells outlined with a dashed line, each with a sum in its corner.

The digits in a cage add up to exactly that sum, and a digit never repeats inside a cage. PlayWord gives you three Killer Sudokus every day, from easy to hard, free and without signing up. Each has exactly one solution, and each can be solved without guessing.

How to play

1. Tap a cell, then tap a digit on the number pad. To clear a cell, use Erase or tap the same digit again.
2. The Notes button switches to pencil mode: digits go into the cell as small marks, so you can write down candidates.
3. Digits that break a rule (a repeat in a row, column, box or cage, or a cage that goes over its sum) turn red.
4. When all 81 cells are right, the board is solved. You can switch between the three levels at any time; the clock runs per level.

Tips

• Start with two-cell cages that can only be made one way: 3 is always 1+2, 4 is 1+3, 16 is 7+9 and 17 is 8+9.
• Every row, column and 3×3 box adds up to 45. When cages almost cover a box, the cell sticking out or left over can be worked out by subtraction.
• Note the possible digits of a cage, then cross out the ones its row, column or box already rules out.
• Even the hard level has a few given digits: look first at the cages they narrow down the most.

Strategy

• The rule of 45 is the strongest tool in Killer Sudoku. If the cages covering a 3×3 box add up to 52 and one of them sticks out of the box by a single cell, that cell is 7.
• Unique combinations: on two cells 3, 4, 16 and 17, on three cells 6 (1+2+3), 7 (1+2+4), 23 (6+8+9) and 24 (7+8+9) can only be made one way. They are the best place to start.
• If two two-cell cages in the same row can only take the same pair of digits, those two digits disappear from the rest of the row.

A worked example

Say a vertical two-cell cage with the sum 17 sits at the left edge of the grid. Its cells can only be 8 and 9, so you can remove 8 and 9 from the rest of that column and from the box.

If next to it, in the same 3×3 box, there is a two-cell 3, it can only be 1 and 2. The remaining five cells of the box can then only take 3, 4, 5, 6 and 7.

History of the game

Killer Sudoku began in Japan as sumdoku or samunamupure and became popular in Europe in the mid-2000s, when British newspapers started printing it regularly. Its relative kakuro also builds numbers from sums.

Frequently asked questions

What are the rules of Killer Sudoku?

Every row, column and 3×3 box holds the digits 1–9 exactly once, as in classic sudoku. On top of that, the digits in each dashed cage add up to the number in its corner, and no digit repeats inside a cage.

Where can I find all cage combinations?

On the Killer Sudoku combinations page: it lists every sum of cages with 2 to 5 cells with all possible digit sets, and highlights the unique ones.

What is the difference between sudoku and Killer Sudoku?

The rules are the same, but a Killer Sudoku has almost no given digits. You solve it from the cage sums, so besides logic it takes a little mental arithmetic.

Can a digit repeat inside a cage?

No. All digits in a cage are different, and they add up to exactly the number in the cage's corner.

Is there always exactly one solution?

Yes. A solver checks every board before it is published, and only boards with a single solution go out.

How do the three levels differ?

The easy level has smaller cages and more given digits; the hard level has bigger cages and only a few given digits, so it needs longer chains of reasoning.

What if I get stuck?

The Solution button (tap it twice) shows the board's solution. The level then closes, but it does not count as solved.