Elo rating change after a game: expected score, FIDE K factor and new ratings.
Result
K factor
Per FIDE: 40 for new players and juniors under 2300, 20 under 2400, 10 for players who have reached 2400 or more.
Player A
+10
New rating: 1,510
Expected score: 50%
Player B
-10
New rating: 1,490
Expected score: 50%
Change for Player A across the three outcomes
| Result | Change for A |
|---|---|
| Win for A | +10 |
| Draw | +0 |
| Win for B | -10 |
The Elo calculator shows how a rating changes after a single game using the FIDE formula: enter both ratings, pick a K factor and a result, and it computes the expected score, the change and the new values for both players. It works for chess and for any other game that uses the Elo system.
The expected score of player A against player B is E = 1 / (1 + 10^((Rb - Ra) / 400)). A player rated 200 points higher is expected to score about 76 percent, and with equal ratings the expectation is 50-50.
After the game the new rating is R + K times (S - E), where S is 1 for a win, 0.5 for a draw and 0 for a loss. Surprising results move the rating more than expected ones.
The K factor sets how fast the rating moves. Per FIDE: 40 for new players up to 30 rated games and for juniors under 2300, 20 for players rated under 2400, and 10 for players who have reached 2400 or more.
For a difference above 400 points FIDE counts the difference as exactly 400 when calculating the expected score, so that changes never become negligible. The calculator applies this rule.
It depends on the rating difference and the K factor. With equal ratings and K = 20 a win brings +10, and a win against a much stronger player brings up to about +18.
A draw is half a point. If your expected score is above 0.5 a draw costs rating, and if it is below 0.5 it gains rating.
No, the system is also used in go, backgammon, esports and many online games. The formula is the same.
The formula is the official FIDE one, including the 400 point rule. The official rating however is computed over all games in the rating period and rounded by FIDE, so small differences are possible.