Chess accuracy calculator
Paste a game and get an accuracy percentage for both sides, along with the move-by-move scoring it was built from. No account, no limit, no upload.
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How accuracy is actually calculated
Accuracy is not a measure of how many moves matched the engine. It is a measure of how much you gave away, and it is computed in three steps.
- Each position's evaluation in centipawns is converted to a winning chance between 0 and 100, using the public Lichess logistic model. This is the step that makes the number fair: throwing away a pawn in a level position matters, and throwing away a pawn when you are a rook up does not.
- Each move's cost is the winning chance lost against the engine's own choice, from the mover's side of the board.
- That cost becomes a per-move score on the public Lichess exponential curve, and a side's accuracy is the mean of its own move scores.
Because it averages per-move scores, a game can hold one catastrophic blunder and still read in the eighties. That is intended — accuracy describes the whole game, not its worst moment. The move labels and the graph are where the worst moment shows up.
What counts as a good accuracy
Less than people assume, and it depends heavily on the position type: a quiet game that stayed balanced produces higher accuracies for both players than a sharp one, because there was less to lose on any given move. Comparing your accuracy across your own games is informative. Comparing it to a number someone quoted from a different game is not.
The performance rating, and its real precision
Alongside accuracy each side gets a rating that this game's play was worth. It is fitted to real data rather than guessed: 50 rated games spanning 785 to 2978 were run through this exact pipeline and regressed against the players' actual ratings.
The honest limitation is published too. One game places a player to roughly ±600 Elo, and that is a property of chess rather than of the measurement — a slower, deeper scan measured no better. The signal appears by averaging: error falls with the square root of the number of games, so about ten games reach ±190 and twenty reach ±134. Treat a single game's figure as a description of that game.
Calculate the accuracy of any game
Three ways in: paste the PGN from any site, paste a Chess.com or Lichess game link, or look a Chess.com username up and pick from recent games. Stockfish 18 runs inside your browser tab, so analysis stays local unless you opt into contribution, and nothing is metered.