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Expert Sudoku
Around 26 givens — close to the practical floor for a board with one solution. Expert Sudoku is not harder because there is less information; it is harder because the information is arranged so that nothing falls out early.
What expert difficulty actually means
There is a known lower bound here: no Sudoku with a unique solution can have fewer than 17 givens. Expert boards sit well above that, but they are built so that the first twenty minutes of an easy board's worth of progress simply is not available.
The practical difference is depth. On a hard board a deduction usually spans two units. On an expert board it can span three — a Swordfish across three rows and three columns, or a chain of eliminations where each step only makes sense because of the one before it.
It also means being wrong is expensive. A single mis-marked candidate early in an expert solve can send you twenty minutes down a path that cannot close, which is why careful solvers slow down here rather than speeding up.
How to solve an expert board
Be complete before you are clever. Fill every candidate in the grid before hunting for patterns — an expert board will not reward a partial candidate map, and half the difficulty is bookkeeping.
Work up the technique ladder in order: singles, then pairs and triples, then pointing pairs, then X-Wing, then Swordfish. Reaching for the exotic pattern first is the most common way to spend an hour on a board that had a hidden single in it.
If you genuinely stall, take the smallest possible hint. Asking the solver for one digit and going back to the grid keeps the solve yours; asking for the whole answer ends it.
Every board has exactly one solution
Boards here are carved a cell at a time, and any cell whose removal would leave the grid with two valid answers is put straight back. That is what makes the 26-ish clue count on this page a difficulty rather than a gamble: there is always a deduction available, so you never have to guess and back out.
If you cannot find the next move, the honest fix is a technique rather than a hint. The techniques index covers them in the order they start paying off — or paste the grid into the solver and ask for one digit rather than the whole answer.
Frequently asked questions
What is an expert Sudoku?
Around 26 givens, arranged so that none of the early, easy progress of a simpler board is available. The deductions also run deeper — spanning three units rather than two, as in a Swordfish, or chaining so that each step only makes sense because of the one before it.
What is the minimum number of clues a Sudoku can have?
Seventeen. It was proved by exhaustive computer search in 2012 that no Sudoku with 16 or fewer givens can have a single solution. Expert boards sit comfortably above that floor.
How do I stop making mistakes on expert boards?
Fill every candidate in the grid before hunting for patterns, and keep them accurate as you go. On an expert board a single stale pencil mark can send you twenty minutes down a line that cannot close, which is why careful solvers slow down here rather than speeding up.
Are expert Sudoku puzzles solvable without guessing?
Yes. Every board here has exactly one solution, so a complete chain of deductions always exists. The difficulty is finding it, not whether it is there.
Keep reading
Then try it under a clock
Action Sudoku puts a second person on the same grid, racing you cell by cell. Free on iOS and Android, with a daily puzzle and a solo journey when you would rather play alone.