Chess accuracy calculator
Paste a game to calculate both players’ accuracy and inspect the score behind every move.
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How accuracy is 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 keeps 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
Each side also gets a rating estimate for the game. 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.
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.