Where does Elo come from?
The system was devised by Arpad Elo, a Hungarian-American physicist and chess player. The idea is simple: a rating is a number that estimates your strength, and the rating difference between two players predicts who is likely to win, and how convincingly.
Expected score
Before the game the system calculates your expected score, how many points you "ought to" get. If you and your opponent have the same rating, the expectation is 0.5 (a draw is the fair result). If your opponent is 200 points stronger, your expectation drops to about 0.24.
The formula is: E = 1 / (1 + 10^((Ropponent - Ryours) / 400)). You do not have to memorise it; what matters is understanding the logic.
How the rating changes
After the game the actual result (1 for a win, 0.5 for a draw, 0 for a loss) is compared with the expected one:
new rating = old + K x (result - expectation)
Example: you are rated 2000, you play someone rated 2200 and win. Your expectation was about 0.24 and you scored 1. With K=20 that is 20 x (1 - 0.24), roughly +15 points. Had you lost as the weaker player, you would have lost only about 5. That is why beating a stronger player is "expensive" and losing to a weaker one hurts.
The K-factor
K determines how quickly a rating changes:
- K = 40 - newcomers (until they have played 30 games) and players under 18 rated below 2300
- K = 20 - everyone below 2400
- K = 10 - those who have once crossed 2400 (the elite, whose rating is more stable)
Standard, rapid and blitz
FIDE keeps three separate ratings: standard (longer time controls), rapid and blitz. You are the same person, but the numbers can differ quite a lot.
How you get onto the FIDE list
You need to play at least 5 games against already rated opponents (they can be added up across several tournaments) and score at least half a point. The lowest possible starting rating today is 1400.
What the number means
- ~1400-1700 - a beginner or a developing club player
- ~2000 - a solid, serious club player; you know what you are doing
- ~2200-2300 - master level (CM/FM)
- ~2400 - international master strength, practically a semi-professional
- 2500+ - grandmaster territory
In other words, between 2000 and 2400 there is a whole world of work, but every game you play moves your number in the right direction.
Click every square the piece may move to, then press Check. Optional, but the best way to practise.