How to play
Kakuro looks like a crossword, but the answers are numbers and the clues are sums. The grid is split into dark clue cells and white cells you fill in. Every white cell takes one digit from 1 to 9.
Reading a clue. Dark cells carry one or two numbers separated by a diagonal. The number in the upper right corner is the total for the white cells running to the right of it, up to the next dark cell or the edge. The number in the lower left is the total for the white cells running down beneath it. Each unbroken line of white cells is called a run, and every run is between two and nine cells long.
Two rules. The digits in a run must add up to its clue, and no digit may appear twice in the same run. Every white cell belongs to exactly one across run and one down run, so each digit you write has to satisfy both.
Entering digits. Tap a white cell, then tap a digit on the pad below the grid, or type it on a keyboard. The arrow keys move the cursor, and Backspace or Delete clears a cell. Erase does the same with a tap. Undo steps back through your changes.
Built-in checking. A cell turns red when it repeats a digit already in its run, when the digits in a run already exceed the clue, or when a run is complete but adds up to the wrong total. A mistake that doesn’t break any of those rules yet isn’t flagged, so a red cell means something is definitely wrong, while no red doesn’t prove you’re right.
Hint. Press Hint and the game first corrects any cell where you’ve written a wrong digit; if there are none, it fills the next empty cell. The number of hints you used is shown with your time when the puzzle is solved.
The grids
Each puzzle is generated fresh when you start it, with a symmetric pattern of dark cells and a guaranteed single solution. Choose a size under Difficulty:
- Easy: a 6 × 6 grid, including the clue row and column, with roughly 15 white cells.
- Medium: 8 × 8, with roughly 28 white cells.
- Hard: 10 × 10, with roughly 46 white cells.
Some cells start with a digit already printed in them. The generator adds these only where a pattern would otherwise allow two answers, so they’re the minimum needed for uniqueness. Expect about three on Easy and around nine on Hard. Bigger grids take a few seconds to create; a “Creating a new puzzle” message shows while that happens.
Strategy
Memorise the locked combinations. For every run length, the two smallest and the two largest totals can each be made only one way:
| Cells | Smallest | Largest | ||
|---|---|---|---|---|
| 2 | 3 = 1+2 | 4 = 1+3 | 16 = 7+9 | 17 = 8+9 |
| 3 | 6 = 1+2+3 | 7 = 1+2+4 | 23 = 6+8+9 | 24 = 7+8+9 |
| 4 | 10 = 1+2+3+4 | 11 = 1+2+3+5 | 29 = 5+7+8+9 | 30 = 6+7+8+9 |
Spot one of these and you already know which digits the run uses, even if not their order.
Intersect the two runs. A cell’s digit must appear in both of its runs’ possible sets. When an across run of 4 (so 1 and 3) crosses a down run of 3 (so 1 and 2), the shared cell can only be 1. Most puzzles open up from a few crossings like this.
Use the missing digit. The digits 1 to 9 add up to 45. A nine-cell run contains every digit once. An eight-cell run is missing exactly one digit, and that digit is 45 minus the clue: a clue of 39 means the 6 is absent.
Watch the extremes. A 9 can’t go in a two-cell run of 9 or less, and a 1 can’t sit in a two-cell run of 11 or more. Ruling out big and small digits trims options quickly in short runs.
Close out runs. When all but one cell of a run is filled, the last digit is the clue minus the rest. Then check its crossing run: that new digit often finishes the other direction too.
Prefer logic to Hint. Hints are counted on the final screen. On Hard, try to finish with none.
If you like adding up cages of cells, Math Cages puts arithmetic cages inside a Latin square, and Sudoku drops arithmetic entirely.
If you enjoy Kakuro, try Killer Sums or Light Up next.
