Sudoku Strategies and Tips: How to Solve Sudoku Step by Step
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To solve a sudoku, work in a fixed order: first scan one digit at a time for the only cell in a box where it can go (Hidden Single), then pencil in the candidates and fill any cell with a single candidate (Naked Single). When that stops working, look for Pointing Pair and Naked Pair patterns to remove candidates. You never need to guess.
Step 1: Scan one digit at a time
Start with the digit that already appears most often on the grid. For each copy, imagine a line running across its row and down its column, and cross off the cells those lines pass through.
Now look at each box that doesn't have that digit yet. If only one empty cell in the box is not crossed off, the digit must go there. This is a Hidden Single, and on easy puzzles it does most of the work.
Go through the digits 1 to 9 this way, then repeat: every number you place creates new crossings.
Step 2: Check rows and columns too
The same trick works on a row or a column. If a row is missing only a few digits, ask for each missing digit: which cells in this row can still take it? When there is only one, place it.
Rows, columns, and boxes with only two or three empty cells are the quickest wins, so check them first.
Step 3: Write candidates (pencil marks)
When scanning stops giving you numbers, write the possible digits in small print in each empty cell. A cell's candidates are every digit that is not already in its row, its column, or its box.
Any cell left with exactly one candidate is solved. That is a Naked Single. Each time you place a number, erase it from the candidates of every cell in the same row, column, and box.
Step 4: Remove candidates with patterns
Medium and hard puzzles need one more idea: instead of placing a number directly, remove candidates until a cell has only one left. The first patterns to learn are:
- Pointing Pair: if a digit's candidates in a box all sit on one row or column, that digit can be removed from the rest of that row or column.
- Box/Line Reduction: if a digit's candidates in a row or column all sit inside one box, it can be removed from the rest of that box.
- Naked Pair: if two cells in a unit have the same two candidates and nothing else, those two digits can be removed from every other cell in the unit.
- Hidden Pair: if two digits can only go in the same two cells of a unit, every other candidate can be removed from those two cells.
Step 5: Repeat the loop
Sudoku is a loop, not a straight line. After every new number or removed candidate, go back to Step 1. A pair you found in one box often creates a hidden single in another.
If you get stuck for real, read our guide to hard sudoku strategies below, or open a hint in the app: the first step shows where to look, the next shows how to think about it, and the last shows the answer with the reason.
Common beginner mistakes
- Guessing: a guess that seems to work can hide an error that only shows up ten moves later. Every number should have a reason.
- Filling candidates too early on easy puzzles: scanning is faster until it stops working.
- Forgetting to erase candidates after placing a number. Most "impossible" positions come from a stale pencil mark.
- Checking only boxes. Rows and columns hide just as many singles.
Frequently asked questions
What is the fastest way to solve a sudoku?
Scan digit by digit for hidden singles first, starting with the digit that appears most often, and only write candidates when scanning stops working. Speed comes from checking units that are nearly full first.
Is there a trick to solving every sudoku?
There is no single trick, but there is an order: singles first, then candidates, then pointing and pairs, then wings and fish for the hardest puzzles. Every well-made sudoku can be finished with logic alone.
Should I use pencil marks?
Yes, once scanning stops giving you numbers. Candidates are what make patterns like Naked Pair and X-Wing visible, and all medium-and-harder puzzles rely on them.
Do you need math to solve sudoku?
No. The digits are only symbols and nothing is added up. Sudoku is pure logic: each digit appears once in every row, column, and box.
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