Cross Sums — the number crossword, free online
Best 5×5: — · Streak 0
Keys: 1–9 enter, arrows move, P notes, U undo, H hint, C check, N new, M mute.
What are cross sums
The crossword made of numbers
Cross sums, also known as Kakuro, is a single-player logic puzzle. The grid looks like a crossword, but the white cells hold digits from 1 to 9. Each dark clue cell gives the total for the run of cells beside or below it, and no digit may repeat inside a run. There is no arithmetic beyond addition — only deduction, and every puzzle has one answer.
- Three grid sizes
- Pick 5×5 for a quick warm-up, 7×7 for the everyday puzzle, or 9×9 for the full challenge. Times and streaks are tracked per size.
- Always one solution
- Each puzzle is generated on your device and verified by a solver, so there is exactly one answer and never a need to guess.
- Notes, hints, undo
- Pencil candidate digits, undo any move, reveal a hint, or check for wrong digits. Runs turn green as you complete them.
- Progress saved locally
- Best times, no-hint times, and streaks for each size are stored on your device — never on a server. No account needed.
How to play
How to play cross sums
Cross sums is a game of deduction. Read the clue, choose digits that never repeat in a run, and make every crossing agree until the whole grid adds up.
- 1
Read the clue cells
Dark cells with a diagonal line are clues. The number in the top-right corner is the total for the run of white cells to its right (across). The number in the bottom-left corner is the total for the run of white cells below it (down). Cells with no clue on a side simply start no run that way.
- 2
Fill runs with different digits
Every white cell holds a digit from 1 to 9. Inside a single run, each digit may be used only once, and the digits must add up to the clue. A run of three cells with the clue 7 can only be 1, 2 and 4 in some order.
- 3
Cross-check every intersection
Each white cell belongs to two runs, one across and one down, and must satisfy both. A digit that fits its across run may break its down run. Solving is the process of narrowing the options where the two runs meet.
- 4
Finish the grid
Keep placing digits until every run is complete. A clue turns green once its run is full and correct. Repeated digits and over-sized sums are marked in red as you go. The puzzle is solved the moment the last run adds up.
Tips to win more games
- Start with the two-cell runs. Clues of 3, 4, 16 and 17 have only one possible pair of digits.
- Memorise the unique combinations for longer runs too: 6 and 7 in three cells, 10 and 11 in four, 23 and 24 at the top end.
- Look for crossings between two runs whose candidate digits share only one value; that cell is forced.
- If a two-cell run must be 1 and 2, any crossing run that already contains a 1 or a 2 elsewhere tells you which way round they go.
- Use pencil notes early. Writing the possible digits in each cell makes forced cells and eliminations visible.
- A long run with a very high or very low sum is nearly complete before you start. Fill it first.
- If you are stuck, hunt for a run where all but one cell is filled — the last digit is just subtraction.
FAQ
Cross sums, answered
Straight answers about the free cross sums puzzle you can play online in your browser.
What are cross sums?
Cross sums are number crosswords. A grid of white and dark cells is filled with digits 1–9 instead of letters. Dark clue cells give the total for the run of white cells that starts beside or below them, and each run must add up to its clue without repeating a digit. The puzzle is solved when every across and down run matches its total.
Are cross sums the same as Kakuro?
Yes. Kakuro is the Japanese name for the same puzzle, which is also sold as cross sums, cross-totals, or a number crossword. The rules are identical: digits 1–9, no repeats in a run, and each run adds up to its clue. This game uses the cross sums name and the standard Kakuro rules.
Is crosssums.app free to play?
Yes. crosssums.app is free with no download, no account, and no paywall. The puzzle runs entirely in your browser on desktop and mobile.
How do you play cross sums?
Select a white cell and enter a digit from 1 to 9. Every run of white cells must add up to the clue in the dark cell at its start, and no digit may repeat inside a run. Because each cell sits in one across run and one down run, you solve by finding digits that satisfy both sums at once.
A clue turns green when its run is complete and correct. When every clue is green, the puzzle is solved.
Can a digit repeat in a cross sums puzzle?
A digit cannot repeat within the same run, but it can appear again elsewhere in the grid, including in a crossing run. For example, a two-cell run with the clue 8 can be 1+7, 2+6, or 3+5, but never 4+4, while a 4 in some other run is fine.
Does every puzzle have exactly one solution?
Yes. Each puzzle is generated on your device and checked with a solver to confirm there is exactly one valid fill. If the random layout would allow more than one, the generator pre-fills and locks a few cells until the solution is unique, so you never have to guess.
What is the difference between the 5×5, 7×7, and 9×9 grids?
The size is the playable area, not counting the row and column of clue cells. 5×5 has short runs and suits beginners, 7×7 adds longer runs and more crossings, and 9×9 can have runs up to nine cells long and needs chained deductions. Times and streaks are tracked separately for each size.
How do I start a cross sums puzzle?
Look for runs with only one possible set of digits. In two cells the clues 3, 4, 16 and 17 are forced; in three cells 6, 7, 23 and 24 are forced. Place or note those digits, then check the runs that cross them.
The tips page has a table of the unique combinations for runs of two to six cells.
Why is my digit red?
A digit is marked red when it repeats within a run, when a run is full but does not add up to its clue, or when a partial run already adds up to more than its clue. Red means a rule is broken, not that the digit is necessarily wrong for the final solution — use Check for that.
Can I play cross sums on my phone?
Yes. The board, number pad, and tools are designed to fit on one phone screen in portrait. Tap a white cell, then tap a number. Pencil notes and undo are one tap away.
Does my progress save?
Best times, best no-hint times, solve counts, streaks, your last grid size, and the sound setting are saved in your browser on this device. They persist across refreshes and are not uploaded anywhere. An unfinished puzzle is not saved; if you start a new one after making moves, the streak for that size resets.