Score = 1 per win, 0.5 per draw, 0 per loss. In multi-game mode the opponent rating is the field average.
About this tool
The Chess Elo Rating Calculator works out how your rating changes after a game (or a batch of games) using the standard Elo system, entirely in your browser — nothing is uploaded. Enter your rating, your opponent's rating, the result and your K-factor, and it shows your new rating live as you type.
The engine first finds the expected score E = 1 / (1 + 10^((Rb − Ra) / 400)), the fraction of a point you are predicted to score against that opponent. Your new rating is Ra + K·(S − E), where S is your actual score: 1 for a win, 0.5 for a draw, 0 for a loss. In multi-game mode you enter the total points scored over G games against an average-rated opponent, and the update becomes Ra + K·(points − G·E).
The K-factor controls how fast ratings move: 40 is common for new or junior players, 20 for most club players, and 10 for masters. Beating a much stronger opponent (high E gap) gains the most points, while losing to a much weaker one costs the most — the expected-score term is what makes the maths self-correcting.
Frequently asked questions
What is the K-factor?
It is the maximum number of rating points a single game can move you. FIDE uses 40 for new players, 20 for most rated players under 2400, and 10 once you pass 2400. A higher K makes your rating react faster but more erratically.
How is the expected score calculated?
E = 1 / (1 + 10^((opponent − you) / 400)). A 0-point rating gap gives E = 0.5 (an even match); every 400 points of advantage makes you about ten times as likely to score the point.
What does multi-game mode do?
It updates your rating over several games against an average opponent at once. Enter the games played and total points scored (wins = 1, draws = 0.5); the new rating is you + K·(points − games·E).
Why did I gain points even after a draw?
If your opponent was rated higher than you, your expected score was below 0.5, so scoring exactly half a point still beats expectation (S − E is positive) and your rating rises.