Elo rating calculator
Enter both ratings, the result and a K factor to see each player's expected score and how many rating points are won or lost. It works for chess, Go, board games and any game rated with Elo.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter your rating and your opponent’s rating.
- Choose win, draw or loss from your side.
- Pick the K factor, or enter your own, and read the new ratings.
Expected score E = 1 ÷ (1 + 10^((R_opponent − R_you) ÷ 400))
New rating = old rating + K × (result − E)
where the result is 1 for a win, 0.5 for a draw and 0 for a loss.
Worked example
Rating 1600 against 1400: E = 1 ÷ (1 + 10^(−0.5)) = 0.760. With K = 32, a win gives 32 × (1 − 0.760) = +7.7 points, a draw 32 × (0.5 − 0.760) = −8.3 and a loss 32 × (0 − 0.760) = −24.3. Beating a stronger player pays much more than beating a weaker one.
Notes
This is the classic Elo update for a single game. Federations add their own rules, such as rating floors, provisional ratings and tournament-wide calculations, which are not modelled here. The FIDE K factors are summarised here for convenience; check the current FIDE rating regulations for the exact wording.
Frequently asked questions
What is the Elo expected score?
It is the average result you should get against this opponent, counting a win as 1, a draw as 0.5 and a loss as 0. The formula is 1 ÷ (1 + 10^((opponent − yours) ÷ 400)). A 400-point lead means an expected score of about 91%.
What K factor should I use?
Use the value your federation or site uses. In FIDE chess the K factor is 40 for new players and for juniors under 2300, 20 while the rating is under 2400, and 10 for players who have reached 2400. Many clubs and online games use 32 or 24.
Does the expected score equal the chance to win?
Not exactly. It counts a draw as half a point, so in chess it mixes the win and draw chances. For games without draws it is the win probability.
Why does the opponent lose exactly what I win?
The calculator gives the opponent the same K factor, which keeps the points balanced. In real systems the two players often have different K factors, so the changes differ - enter each side separately by swapping the ratings.