♟️ Chess Elo Rating Calculator

See what a single game does to a rating. Enter both players' ratings and the result, and this gives the expected score, the exact rating change, the new rating, and the performance rating for that game.

The Elo maths

Expected score E = 1 ÷ (1 + 10(Rb−Ra)/400). New rating = Ra + K × (S − E), where S is the actual result (1, ½ or 0) and K is the rating-change multiplier. A 400-point gap means the stronger player is expected to score about 10 of every 11 points. Performance rating for a single game is simply the opponent's rating ±400.