Work out chess elo rating instantly with clear inputs, formula shown and shareable results.
Elo sets the expected score from the rating difference as 1 / (1 + 10 ^ (difference / 400)), then adjusts by the K factor times the gap between actual and expected results. A 400 point gap implies about a 91% expectation for the favourite, which is why the scale is calibrated in units of 400 rather than arbitrary points.
Expected score
E = 1 / (1 + 10 ^ ((opponent - you) / 400))
New rating
new rating = old rating + K x (score - E)
E = 1 / (1 + 10 ^ ((opponent - you) / 400)). Elo sets the expected score from the rating difference as 1 / (1 + 10 ^ (difference / 400)), then adjusts by the K factor times the gap between actual and expected results.
A 400 point gap implies about a 91% expectation for the favourite, which is why the scale is calibrated in units of 400 rather than arbitrary points.
Enter your rating, opponent rating, your score, k factor. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.