Chess Game Analysis Calculator
Calculate your chess game accuracy score based on blunders, mistakes, and inaccuracies relative to total moves played. Use it after any game to benchmark your performance and track improvement over time.
About this calculator
This calculator produces an accuracy score modeled on how major chess platforms evaluate game quality. The formula is: Accuracy = max(0, 100 − ((blunders × 20 + mistakes × 10 + inaccuracies × 5) / totalMoves × 100)). Each error type is weighted by severity: a blunder costs 20 penalty units (typically a piece-losing or game-losing move), a mistake costs 10 (a move that significantly worsens your position), and an inaccuracy costs 5 (a suboptimal but not immediately harmful choice). These weighted errors are summed and divided by total moves to produce an error rate, which is then subtracted from 100. A score of 90+ indicates a very accurate game; 70–89 is solid; below 60 suggests frequent decision errors. The max(0, …) floor prevents negative scores in catastrophic games.
How to use
Example: You played a 35-move game with 2 blunders, 1 mistake, and 3 inaccuracies. Step 1: Weighted errors = (2 × 20) + (1 × 10) + (3 × 5) = 40 + 10 + 15 = 65 Step 2: Error rate = 65 / 35 × 100 = 185.7 — this exceeds 100, so… Step 3: Accuracy = max(0, 100 − 185.7) = max(0, −85.7) = 0% Better example: 40 moves, 0 blunders, 1 mistake, 2 inaccuracies: Weighted = 0 + 10 + 10 = 20; rate = 20/40 × 100 = 50; Accuracy = 100 − 50 = 50%.
Frequently asked questions
What is a good chess game accuracy score for club-level players?
For players rated 1000–1500 ELO, an accuracy score of 70–80% in a classical game is considered solid, while scores above 85% are excellent. At grandmaster level, engine-assisted analysis typically shows accuracies of 90–95% in well-played games. Blitz and bullet games inherently produce lower accuracy because time pressure forces rushed decisions. It is more useful to track your average accuracy trend over many games than to fixate on a single game score, as individual games have high variance depending on the opponent and position complexity.
What is the difference between a blunder, a mistake, and an inaccuracy in chess?
These three terms describe different magnitudes of error as evaluated by chess engines. A blunder is the most severe—a move that immediately loses material (a piece or more) or decisively worsens the position, often changing the game result from winning to losing. A mistake is a significant error that worsens your position substantially but may not be immediately decisive. An inaccuracy is a suboptimal move that slightly reduces your advantage or slightly worsens a bad position without a dramatic consequence. Engine tools like Stockfish quantify these using centipawn loss thresholds, though thresholds vary by platform.
How can I reduce my blunder rate in chess games?
Reducing blunders requires building the habit of candidate-move thinking: before every move, ask 'does this move hang a piece, allow a fork, or walk into a pin?' Regular tactics training (20–30 minutes daily) builds the pattern recognition needed to spot threats automatically. Time management is equally important—most blunders occur in time pressure, so practicing longer time controls and clock discipline prevents panic moves. Reviewing every blunder after the game with an engine, identifying the moment you stopped calculating accurately, is the most targeted way to eliminate recurring error patterns.