Elo Rating Calculator

Calculate how a single chess game changes both players' Elo ratings. Enter the two ratings, choose the result and a K-factor — the change is computed instantly.

Game result (for Player A)
K-factor
Player A
+16New rating 1516
Player B
-16New rating 1484

Allowed K-factors: 10, 20, 32, 40. A higher K makes each game move your rating faster.

How the Elo formula works

The Elo system first estimates each player's expected score. For player A against player B it is E = 1 / (1 + 10^((RB − RA) / 400)). Equal ratings give an expected score of 0.5; a 400-point rating gap gives the stronger player about a 91% expected score.

After the game, the rating change is ΔR = K × (S − E), where S is the actual score (1 for a win, 0.5 for a draw, 0 for a loss) and K is the K-factor. Beating an equal opponent with K = 32 gains exactly 16 points; upsetting a much stronger opponent gains more, while beating a much weaker one gains almost nothing.

The K-factor controls how fast ratings move: FIDE uses K = 40 for new players and juniors, K = 20 for established players under 2400, and K = 10 for elite players who have reached 2400. Many clubs and online platforms use K = 32 as their standard. Ratings between 100 and 3500 are supported here, which covers every practical chess rating.