The rating system explained

How does the rating system work?

As a chess player, whichever level you are, you have probably heard about the ratings. In a few words, ratings were created to rank the players according to their strength. In that way, a player with 2000 rating is supposed to play better than a player with 1200 rating. Unfortunately, the ratings are not perfect. If we don't understand how the rating system works, we are probably going to make false assumptions and that can lead to bad decisions in the games.

In this article you can find out a brief explanation on the rating system and in the next one we will answer all the possible questions there might be about this topic.

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The ELO System

Named after its creator (Dr. Arpad Elo), the system assigns values to the players, and after the game depending on a few factors those values will go up or down, a player will win points and the other player will lose points. How many points? It depends on:
- Age: under 18 players have a special coefficient (K=40), and after they are 18 all the players are considered the same.

- Current rating: Depending on the current rating a player has the coefficient will also change. For instance, over 2400 use K=10, and under that rating K=20. If you are below 2300 and under 18 years old, as said before your coefficient is still K=40.

This coefficient thing might sound too difficult to understand, so let's use some examples.

Example A:
A player with 1600 rating and 10 years old plays against another player with exactly the same rating (1600). As both players have the same level, the system expects them to make a draw, score 0,5 points each. If one of the players win, they would be getting 0,5 extra points compared to the expected ones. To calculate how many points will the players win or lose we just need to multiply those 0,5 extra points * the coefficient (in this case, young player below 2300, K=40).

The winner will get: 0,5*40 = +20 rating points.

The loser will get -0.5*40 = -20 rating points.

Example B: A player with rating 2400 plays and loses against Magnus Carlsen (2840). For the rating system to work properly, the limit between players has been set in 400 points, so for his opponent Magnus Carlsen only has 2800. And how much rating does his opponent have for Magnus Carlsen? 2840-400= 2440. When the differences are so big, one of the players is expect to lose almost all the time whilst the other one is expected to win almost all the time. It's important to remark the word "almost", as even against the best player in the world you are still expected to score a few points.

The maximum points expected per game is: 0.92

The minimum points expected per game is: 0.08

Now we just need to multiply the expected points * the coefficient, and we have the rating variation. In the example: both players are over 2400, so both have coefficient K=10.

Player: 0 points scored (lost the game) - 0.08 points expected = -0.08. Multiplied by the coefficient: -0.08*10= -0.8 rating points

Magnus Carlsen: 1 point scored (won the game) -0.92 expected points = 0.08. Multiplied by the coefficient: 0.08*10= 0.8 rating points

There are a lot of rating calculators you can use online, the most common one being the FIDE official ones: https://ratings.fide.com/calculators.phtml

Please remember that rating is not too accurate and players are winning and losing points all the time. What really matters is how well you play and trying to do it better every day.