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Chess Elo Rating Update Calculator

New rating after one game given expected and actual score.

Compute the new Elo rating of a chess player after a single game using R' = R + K · (S − E), where E = 1 / (1 + 10^((R_opp − R) / 400)) is the expected score and S is the actual outcome (1 win / 0.5 draw / 0 loss).

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

R' = R + K · (S − E); E = 1 / (1 + 10^((R_opp − R) / 400)).

In depth

Compute the new Elo rating of a chess player after a single game using R' = R + K · (S − E), where E = 1 / (1 + 10^((R_opp − R) / 400)) is the expected score and S is the actual outcome (1 win / 0.5 draw / 0 loss).