Free chess calculator
The rating gap decides the odds. Set your rating and your opponent's, and see your expected score, a win/draw/loss split, and the exact rating swing for each result.
Elo/FIDE-style. The scale is what matters, not the federation.
A 200-point gap is about 76% / 24%. 400 points is roughly 10-to-1.
Higher between evenly-matched, stronger players. It splits the expected score into wins and losses.
How fast your rating moves: 40 for new players, 20 club, 10 for masters.
The whole game of rating is the gap, not the number. Beating someone 100 points above you is worth +13 because the formula already expected you to score 36%. Play up, and losses cost little while wins pay a lot — the reason improvers are told to seek stronger opposition.
From the rating difference alone, using the standard Elo logistic curve on a 400-point scale: a gap of 0 is 50%, about +200 is 76%, and +400 is roughly 91%. It predicts your average points per game, not any single result.
Because the rating change is your K-factor times the difference between what you scored and what the formula expected. Against someone rated well above you the formula expected you to lose, so a win is a big surprise and pays out; against someone well below, a win was expected and barely moves you.
Roughly 40 for new or provisional players, 20 for established club players, and 10 for masters and high-rated players. A higher K makes your rating move faster and swing more per game.
Turn a rating gap into a probability and plain odds — and see why the curve is an S, not a line.
Your most likely total over N games at a given rating gap, plus the honest spread around it.
Turn a tournament score into the rating you actually played at — the number a good event is really worth.
Educational chess content. Rating math uses the standard Elo model; results are estimates and vary by federation, pool and time control.