How to play Kakuro

A crossword with digits: each run of white cells adds up to its clue, using 1–9 without repeats. Also known as Cross Sums.

▶ Play Kakuro ⊞ Open the solver ∑ Combination calculator

The rules

The grid has black clue cells and white cells. A clue cell shows the total for the run of white cells to its right (across) and/or below it (down).
Fill every white cell with a digit from 1 to 9.
The digits in a run must add up to its clue.
No digit may repeat within a run.

Playing Kakuro on Puzzle Solvers

Choose a grid size and a difficulty, then press Generate Puzzle.
Click a cell and type a digit, or use the on-screen keypad. Notes switches to pencil marks.
Undo steps back; Force places one digit that has only one possible value; Check marks mistakes in red without giving away the answer.
Stuck? Send to Solver opens the same puzzle in the step-by-step solver. Send to Slate opens it as a board on the Slate whiteboard, to solve in front of a class.

Open the Kakuro game →

Using the Kakuro solver

① Build: click cells to toggle black and white. Click a black cell next to white cells to enter its across and down totals.
Pre-fill any digits you already know with the keypad.
② Check, then ③ Solve: step through each run combination and crossing, explained.
Or press Send to Solver inside the Kakuro game to import a puzzle.

Open the solver →

A worked example

An across run of two cells totals 4, so it is 1 and 3. A down run of two cells through its first cell totals 3, so it is 1 and 2.

The shared cell must be in both {1, 3} and {1, 2} — only 1 fits. So the crossing cell is 1, the rest of the across run is 3 and the rest of the down run is 2.

Strategies

Start with unique sums. Some totals have only one combination: 3 in 2 cells (1+2), 4 in 2 (1+3), 16 in 2 (7+9), 17 in 2 (8+9), 6 in 3 (1+2+3), 24 in 3 (7+8+9).
Cross the runs. A cell belongs to an across run and a down run. Only digits allowed by both can go there — the intersection often leaves one choice.
Must-have digits. A 4-cell run totalling 11 is always 1+2+3+5, so it must contain a 5 even before you know where.
Small and large ends. Low totals force small digits and high totals force large ones. A 2-cell 15 can only use 6, 7, 8 and 9.
Use the calculator. The run calculator lists every combination, filters out digits you have placed and finds the shared digits at a crossing.

Common mistakes

Repeating a digit within a run because the sum works — 2+2 is never allowed.
Using 0. Kakuro digits are 1 to 9.
Ignoring the crossing run. Most deductions come from the cell where two runs meet.

Where it comes from

Cross-sum puzzles were published in American magazines from the 1950s. A Japanese publisher gave them the name Kakuro, and they spread with the Sudoku boom in the 2000s.

Frequently asked questions

What does a clue cell with two numbers mean?

The number in the upper-right is the total for the run going across; the one in the lower-left is the total for the run going down.

Are there combination charts for Kakuro?

Yes — see the Kakuro combinations chart, which lists every total for runs of 2 to 9 cells and marks the ones with a single combination.

Can I solve a Kakuro from a book?

Build it in the Kakuro Solver: click cells to make them black, enter the clues, then solve step by step.

Is Kakuro harder than Sudoku?

It needs some arithmetic and combination knowledge, but the logic is similar. Easy Kakuro is a good next step after Sudoku.

What is the largest run?

Nine cells, which must contain every digit 1–9 and so always totals 45.

Keep going

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