Chessy
What Is the Elo Rating System?
The Elo rating system is a method that predicts results from the gap between two players' numbers and adjusts each rating up or down after every game. Named after physicist Arpad Elo, it's the foundation for chess ratings worldwide, from FIDE's official system to the ratings used by Chess.com and Lichess.
How the prediction works
The bigger the rating gap between two players, the more lopsided the expected result. A 200-point rating advantage suggests the stronger player should win roughly 75% of the 'points' available (counting a win as 1, a draw as 0.5, and a loss as 0) in games between them over time. Elo doesn't predict individual game outcomes — it predicts long-run statistical tendencies.
How ratings change after a game
After each game, both players' ratings shift based on the difference between the actual result and what Elo predicted:
- Beating a much higher-rated opponent gains you many points, since it was 'unexpected'
- Beating a much lower-rated opponent gains you very few points, since it was 'expected'
- A draw between closely matched players barely moves either rating
The size of these swings is also scaled by a K-factor, a number that controls how quickly a rating can move — newer or less experienced players typically have a higher K-factor so their rating adjusts faster while it settles at an accurate level.
Elo across different platforms
Although Elo is the underlying math behind most chess rating systems, the specific number you see can vary a lot between platforms and even time controls, because each pool of players and each set of starting conditions is different. This is why a rating on one site or system isn't directly comparable to a rating on another — the formula is shared, but the population it's calibrated against is not.
Frequently asked questions
Who invented the Elo rating system?
Physicist Arpad Elo developed it in the 1960s, and FIDE adopted it as the official chess rating system in 1970.
Can Elo ratings go down?
Yes — losing, especially to a lower-rated opponent, decreases your rating, and ratings can rise or fall after every single game.
Does drawing always keep my rating the same?
No — a draw against a much higher-rated opponent will raise your rating, while a draw against a much lower-rated opponent will lower it, since Elo compares the actual result to the expected one.
Is Elo only used in chess?
No — while it originated in chess, the same core math is used to rate players and teams in many other games and sports today.