How to play Kakuro
Kakuro is a crossword made of numbers. Instead of word clues, each across and down run of white cells has a sum written in the split ink square at its start.
Fill every white cell with a digit from 1 to 9 so that each run adds up to its clue and no digit appears twice in the same run.
Rules
- The number above the diagonal of a clue square is the sum of the run to its right; the number below the diagonal is the sum of the run beneath it.
- Only the digits 1–9 are used, and a run never repeats a digit — so 4 in two cells must be 1 + 3, never 2 + 2.
- Repeated digits in a run are marked. A clue that is already exceeded, or a finished run that adds up wrong, is underlined; a run that adds up fades its clue.
- Choose Easy (6 × 6), Medium (8 × 8) or Hard (10 × 10). Bigger grids have more and longer runs.
- A hint fills in one correct digit, but solves that used hints don’t count towards your best time. Your progress is saved separately for each size.
Controls
- Click / tap a white cell
- Select it, then pick a number on the pad (or drag a number onto a cell)
- 1–9
- Place a digit (Shift + digit adds a note)
- Arrows / WASD
- Move to the next white cell
- N
- Toggle notes mode
- M
- Toggle auto notes (off clears all notes)
- C
- Show or hide the sums helper
- Backspace / 0
- Erase
- Z / Ctrl+Z
- Undo
- H
- Hint
- P
- Pause
Tips
- Learn the runs with only one answer: 3 in two is 1 + 2, 4 in two is 1 + 3, 16 in two is 7 + 9, 17 in two is 8 + 9, 6 in three is 1 + 2 + 3 and 24 in three is 7 + 8 + 9.
- Look where an across run and a down run cross: the digit there has to belong to both runs’ possible sets. Often only one digit does.
- Turn on Sums to see every set of digits that can make the selected runs. Sets that clash with digits you’ve already placed are struck out.
Kakuro strategy
Every length has four certain sums
For any run length, the two smallest and two largest totals have only one set of digits. In three cells, 6 and 7 are 1 2 3 and 1 2 4, and 23 and 24 are 6 8 9 and 7 8 9. In four cells, 10, 11, 29 and 30. In five, 15, 16, 34 and 35. Hard grids have runs of up to six, where 21, 22, 38 and 39 each have a single set.
Digits every set shares
A clue with several sets can still pin a digit. Eight in three cells is 1 3 4 or 1 2 5, so the run contains a 1. Twenty-two in three is 5 8 9 or 6 7 9, so it contains a 9. It also works the other way. Fifteen in two is 6 9 or 7 8, so neither cell can hold anything below 6, and ten in two never uses a 5.
Work with the remainder
Once some digits are placed, work with the remainder. A four-cell run of 20 with a 9 and a 1 in it needs 10 from two cells, using neither 9 nor 1. That leaves 2 8, 3 7 or 4 6. Cross that short list with the down run through each empty cell. Late in a puzzle the remainders are small, and they often have only one possible pair.
Where auto notes stop
Auto notes keep every cell at the digits that fit both of its runs, and they are recomputed after each digit you place. So any note you strike by hand comes back. What they never do is look across a run: if a 9 is needed in a run and only one cell can take it, the notes still show 9 among others there. That step is yours.
About Kakuro
Number puzzles laid out like a crossword of sums were printed in American puzzle magazines in the middle of the twentieth century; Dell called them Cross Sums. In the 1980s the Japanese publisher Nikoli took them up as kasan kurosu, “addition cross”, which got shortened to Kakuro. After Sudoku took off in 2005, British newspapers went looking for the next number puzzle and Kakuro was waiting.
Every grid here is generated fresh: a symmetrical pattern of blocks, digits filled in and then reworked until the clues pin down a single answer that can be reached run by run, without guessing. On top we added pencil notes, auto notes, a sums helper, hints, undo and a saved game for each size.
Questions
How do you read a Kakuro clue?
Each clue square is split by a diagonal. The number in the top-right half is the total of the white run to its right; the number in the bottom-left half is the total of the run below it.
Can a digit repeat in Kakuro?
Not within a run. The same digit can appear many times in the grid, just never twice in one across or down run.
Does every puzzle have one solution?
Yes. Each puzzle is checked by a solver and is built so that it can be finished by working out what each run allows, one step at a time, with no guessing.
What does the Sums button do?
It lists every set of different digits that adds up to the selected cell’s across and down clues, and strikes out sets that don’t contain the digits already in that run. It’s a reference, not a hint, so it doesn’t affect your time.