What to Do When You Are Completely Stuck
By Sudoku a Day ·
Sudoku a Day Blog
Every Sudoku solver gets stuck sometimes. It does not matter whether you are a beginner or an experienced player. There will be moments when the grid seems impossible and no number wants to go anywhere.
Start by checking for mistakes and overlooked deductions. These steps can help you decide what to try next; they do not guarantee that a familiar technique will solve every position.
Step 1: stop and breathe
When you feel stuck, your first instinct might be to scan faster or start guessing. Resist both. Take a breath. Focus on finding one placement or elimination you can explain from the current grid.
Working methodically can make it easier to check your reasoning. Pause after each deduction and verify it before placing a digit.
Step 2: re-check your existing placements
Before looking for new moves, make sure your current numbers are correct. A single wrong placement early in the puzzle can make everything downstream impossible. Check your most recent 3 to 5 placements against their row, column, and box constraints, then revisit the reasoning behind each placement. A wrong digit can avoid an immediate duplicate, so passing the duplicate check alone does not prove a placement is correct.
If you find an error, fix it and the puzzle will likely open up again.
Step 3: update your pencil marks
If you are using pencil marks, they might be stale. Go through every row, column, and box and remove candidates that conflict with numbers you have placed since your last mark update. Outdated marks hide valid deductions.
If you are not using pencil marks yet, this is a good time to start. Write candidates in the cells that are giving you trouble. Seeing the possibilities on paper often reveals patterns that are invisible in your head.
Step 4: scan one number at a time
Pick a single number, say 4, and check every row, column, and box on the grid. Where can 4 still go? Are there any units where 4 only has one possible position? This focused scan is more effective than general browsing because it forces you to be systematic.
Do this for all nine numbers. If you find no forced placement, update your candidates and move on to another deduction instead of assuming a single must be available.
Step 5: look for pairs and interactions
If single-number scanning does not help, look for hidden singles: a number that can only go in one cell within a row, column, or box, even if that cell has multiple candidates.
Also check for naked pairs: two cells in the same row, column, or box that each contain the same two candidates and no others. Those candidates can be eliminated from all other cells in that unit.
Step 6: take a break
If frustration makes it hard to concentrate, take a break for as long as suits you. You may notice something different when you return, but a break does not guarantee a new deduction.
A break can help you return with more patience. When you resume, check the grid systematically; a fresh look does not replace a valid deduction.
When the puzzle is genuinely beyond your level
If you have tried everything and are still stuck, the puzzle might require a technique you have not learned yet. That is completely normal. Check out our strategy guides to learn the next technique for your level.
When your puzzle includes an answer key, use it to check a result, not as proof of why a move follows logically. For practice, our printable packs with answers pair their own puzzles with solutions; they do not necessarily contain the puzzle you are currently solving. To learn a deduction, work through a strategy example step by step.
Do not let one tough puzzle discourage you. Getting stuck is part of the learning process. Try today's daily puzzle at a comfortable level and keep building your skills.