Elo Rating Calculator

How to use

1. 1Pick a mode: Single game for one match between two players, or Tournament for a full round against multiple opponents.
2. 2Pick a K-factor preset that matches your rating pool (FIDE, USCF, or chess.com), or pick Custom K-factor to enter your own value for a private ladder.
3. 3Enter the ratings. In Single game mode, type both player ratings and pick the result for Player A. In Tournament mode, type your starting rating and add a row for each opponent with their rating and the result.
4. 4Read the expected score, win probability, rating change, and new rating in the result cards. Both the rounded value (FIDE style) and the exact decimal change are shown.
5. 5Click Copy summary to put a plain-text report of the calculation on your clipboard.

About this tool

Elo Rating Calculator uses the original Arpad Elo formula to compute the expected score, win probability, and rating change for any two players, plus a tournament mode that sums the change across every game in a round. The expected score formula E = 1 / (1 + 10^((Ropp - Rme) / 400)) treats a 400-point rating gap as a ten-to-one favorite (about 91 percent expected score), a 200-point gap as roughly 76 percent, and a 100-point gap as roughly 64 percent. After the game, the rating moves by K times the difference between the actual score (1 for a win, 0.5 for a draw, 0 for a loss) and the expected score, so a strong favorite who wins barely moves while an underdog who beats a higher rated opponent collects a large jump. The K-factor presets cover the values used by the major rating pools: FIDE 40 for unrated and provisional players under 30 games, FIDE 20 for the established pool under 2400, FIDE 10 for masters at or above 2400, the chess.com 32 / 24 / 16 used in classical / rapid / blitz, and the USCF 24 used at most regular events. A custom K accepts anything from 0 to 200 for casual ladders, in-house company pools, board game leagues, sports rankings, and any other Elo-like system. Tournament mode chains as many games as you need (up to 200), evaluates each one against the original starting rating (the FIDE event-report convention so the order of games does not change the result), and reports the round score, the expected score, the average opponent rating, the rating change, the new rating, and the FIDE performance rating computed with the published linear table. Each row in the tournament view shows the per-game expected score and the per-game rating swing, so you can see at a glance which results helped or hurt the most. Useful for chess players checking how much a result will move their rating, tournament directors validating event reports, parents and coaches reviewing scholastic results, board game and esports community leagues running their own Elo pools, and anyone who wants to understand the standard win-probability formula behind every modern rating system. All math runs locally with ordinary IEEE 754 doubles, so the ratings and games you enter never leave this browser tab.

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