Chess Rating Calculator

This runs the Elo arithmetic behind a chess rating. Give your rating, the opponent's and the result with a K factor and it returns the expected score, the change and the new rating, along with what a win, a draw and a loss would each have been worth; a second action does the same for a whole event against an average opponent rating, and a third turns a tournament score into a performance rating, both by the usual linear formula and on the Elo curve itself. Lichess and Chess.com run Glicko instead, which also tracks how settled each rating is, so their numbers will differ. A performance rating reflects one event, not a rating.