Understanding Chess Accuracy Ratings: What the Numbers Really Mean

What is Chess Accuracy?

Chess accuracy is a metric that measures how closely your moves match the best moves suggested by a chess engine. It’s expressed as a percentage, where 100% would mean every move was the engine’s top choice.

How is Accuracy Calculated?

Step 1: Analyze Each Move

The engine evaluates every position in your game and determines the best move along with its evaluation.

Step 2: Calculate Centipawn Loss

For each move you played, the engine calculates how much “value” you lost compared to the best move. This is measured in centipawns (1/100th of a pawn).

Example:

• Best move evaluation: +1.50 (you’re up 1.5 pawns)
• Your move evaluation: +0.80
• Centipawn loss: 70 centipawns

Step 3: Convert to Win Probability

Raw centipawn values are converted to win probability using a formula. A position evaluated at +1.00 might give you ~65% win probability.

Step 4: Average Across All Moves

Your accuracy is the average of how much win probability you preserved across all moves.

The Lichess Formula

chess.rodeo uses the same formula as Lichess:

Win% = 50 + 50 * (2 / (1 + exp(-0.00368208 * centipawns)) - 1)
Accuracy = 103.1668 * exp(-0.04354 * (Win% lost per move)) - 3.1669

This produces accuracy values between 0% and 100%, with typical games falling between 50% and 95%.

What is a Good Accuracy?

By Rating Level

By Time Control

Faster games typically have lower accuracy:

• Bullet (1 min): 5-10% lower than your potential
• Blitz (3-5 min): Average accuracy for your level
• Rapid (10-15 min): Slightly above average
• Classical (30+ min): Best possible accuracy

Understanding Move Classifications

Accuracy is related to, but different from, move classifications:

Move Types and Typical Centipawn Loss

Why Accuracy Varies Between Platforms

You might notice slightly different accuracy scores on Chess.com, Lichess, and chess.rodeo. Here’s why:

1. Engine Depth

Deeper analysis finds more accurate “best” moves. A move that looks best at depth 15 might not be best at depth 25.

2. Multi-PV Settings

Some platforms analyze multiple lines, others focus on the single best move.

3. Formula Differences

While similar, each platform tweaks the accuracy formula slightly.

4. Position Selection

Some platforms exclude certain positions (like forced moves or opening book moves).

Common Misconceptions

“100% Accuracy is Perfect Play”

Not exactly. 100% accuracy means you matched the engine’s choices, but the engine isn’t truly “perfect” — it just plays the best moves within its calculation limits.

“Higher Accuracy Always Means Better Play”

Not always. You could have 95% accuracy in a losing game if you made one catastrophic blunder and then defended accurately. Meanwhile, 85% accuracy in a complex, fighting game might show better practical chess.

“My Accuracy Should Match My Rating”

Accuracy is position-dependent. A tactical game with many forcing moves might show higher accuracy than a complex positional struggle, regardless of who’s playing.

How to Improve Your Accuracy

1. Take Your Time

In longer games, spend time on critical decisions. Most accuracy loss comes from a few bad moves, not consistent small errors.

2. Check for Tactics

Before every move, look for tactics — yours and your opponent’s. Many blunders are simply missed tactics.

3. Review Your Games

Use chess.rodeo to identify your typical mistakes. Do you blunder in time pressure? Miss certain tactical patterns?

4. Study Endgames

Endgame accuracy is often lower because the engine knows complex technical wins. Learning basic endgames helps tremendously.

Conclusion

Accuracy is a useful metric for tracking improvement, but don’t obsess over it. Focus on understanding your mistakes rather than chasing a specific number. A 75% accuracy game where you learned something is more valuable than a 90% accuracy game you don’t remember.

Check your accuracy — Import your games and see how you measure up.