Sudoku FlowWhy Won't My Sudoku Solve? A Checklist
Stuck, or facing a cell with no options? A step-by-step checklist to tell a hidden mistake from a hard step, and what to do about each.
Updated 2026-10-04
Stuck or broken?
A Sudoku stops moving for one of two reasons. Either a mistake has made the board impossible, or the next step needs a technique you haven't used yet. The fix is different, so tell them apart first.
Signs of a mistake
Any one of these means the board can no longer be completed. A proper Sudoku has exactly one solution, so the puzzle isn't broken: a digit is wrong somewhere.
- A cell has no candidates left.
- A digit has no possible cell in some row, column or box.
- Two cells in the same row, column or box can each only be the same digit.
- A digit appears twice in a row, column or box.
If it's a mistake
- Find the repeat or the impossible cell, then look at the digits that caused it.
- Go back to the last digit you are sure of and undo everything after it.
- Recheck your notes: in each cell, clear the digits already placed in its row, column and box.
- Continue, placing only digits you can explain.
If it's a hard step
If nothing is impossible and nothing repeats, the board is fine and you need a stronger technique. Look for pairs first: when two cells in a row, column or box share the same two candidates and nothing else, those two digits can be removed from every other cell in that unit. After pairs come pointing pairs, X-Wings and chains.
Avoid it next time
Most stuck games come from a handful of habits. Our list of the seven most common Sudoku mistakes shows each one and the simple fix.
Practice
Every Find the Mistake puzzle on this site has exactly one wrong digit, and you can play each board right on its page.
