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Chess Ratings - How They Work

  • erik
  • | Aug 23, 2007

Like it or not, we ALL have a chess rating. You may not care at all about your rating, or you may be whining every time it goes down in the slightest. You might be someone who plays a game a year, or someone who plays 1,000 a day. Still, there is a number out there that represents how well you play chess. Well, that's the theory, anyway.

To understand chess ratings you have to understand two things: #1 - that you have a TRUE rating that perfectly represents your strength of play, and #2 - that that TRUE rating will never be known and so we have to use statistics to get as close as possible to the truth. I'm writing this article in response to many people who ask about ratings and need a simple explanation of how they work. (I only know about all this because of a recent super-in-depth statistics course I took and my research in building Chess.com!)

There are two main rating systems, and each one has its merits.

The Elo System (used by the United States Chess Federation, FIDE, and many other online chess sites) is popular for two reason - it has been around for a long time, and it is simple. The idea is this: given two chess players of different strengths, we should be able to calculate the % chance that the better player will win the game. For example, Garry Kasparov has ~100% chance of beating my 4-year-old daughter. But he may only have a ~60% chance of beating another Grandmaster. So when playing that other Grandmaster, if he wins 6 games out of 10, his rating would stay the same. If he won 7 or more, it would go up, and 5 of less, his rating would go down. Basically, the wider the spread of the ratings, the higher percentage of games the higher rated player is expected to win. So to calculate a person's rating after playing a few games you calculate the average ratings of his opponents, and then how many games he was expected to win, and then plug it into a formula that spits out the new rating. Simple enough. Well, it turns out, that is maybe TOO simple.

The Glicko System (used by Chess.com, the Australian Chess Federation, and some other online sites) is a more modern approach that builds on some of the concepts above, but uses a more complicated formula. (This only makes sense now that we have computers that can calculate this stuff in the blink of an eye - when Elo created his system they were doing it on paper!) It is a bit trickier than the Elo system, so pay attention. With the Elo system you have to assume that everyone's rating is just as sure as everyone else's rating. So my rating is as accurate as your rating. But that is just not true. For example, if this is your first game on Chess.com and you start at 1200, how do we really know what your rating is? We don't. But if I have played 1,000 games on this site, you would be much more sure that my current rating is accurate. So the Glicko system gives everyone not only a rating, but an "RD", called a Rating Deviation. Basically what that number means is "I AM 95% SURE YOUR RATING IS BETWEEN X and Y." (Nerd Fact: In technical terms this is called a "confidence interval".) If this if your first game on Chess.com I might say, "I am 95% sure that your rating is somewhere between 400 and 2400". Well that is a REALLY big range! And that is represented by a really big RD, or Rating Deviation. If you have played 1,000 games and your rating is currently 1600 I might say "I am 95% sure your rating is between 1550 and 1650". So you would have a low RD. As you play more games, your RD gets lower. To add one extra wrinkle in there, the more recent your games, the lower your RD. Your RD gets bigger over time (because maybe you have gotten better or worse over time - I'm just less sure of what your actual rating is if I haven't seen you play recently). Now, how does this affect ratings? Well, if you have a big RD, then your rating can move up and down more drastically because your rating is less accurate. But if you have a small RD then your rating will move up and down more slowly because your rating is more accurate. The opposite is true for your opponent! If they have a HIGH RD, then your rating will change LESS when you win or lose because their rating is less accurate. But if they have a LOW RD, then your rating will move MORE because their rating is more accurate.

I wish there was some simple analogy to explain all this, but there isn't. It all comes back to this: you have a theoretically exact chess rating at any given moment, but we don't know what that is and so we have to use math to estimate what it is. There are really smart people out there who work on this stuff for a living, and at the end of it all we get to put their proven methods into our code so that we can all enjoy knowing what little numbers next to our name we deserve.

If you want to read more, check out these articles (WARNING - SEVERE NERD CONTENT AHEAD):

- The Glicko System by Professor Mark Glickman, Boston University

- Introduction to Chess Ratings (Elo mostly) on About.com


  • 14 months ago


    @spanishfly25  - at the end

  • 14 months ago


    I am sorry, I don't feel like reading all the post and the many pages to see if anyone ask my question so here I go again, does anyone in here know if a rating is calculated base on your rating at the begining of the game or at the end of the game,  example at the begginning of the game, I am at 1600 and playing at guy with a rating of 1400, but after 3 months, our ratings are now at 1500, and if the game was going to end now.  would the rating adjustment would be done base on the  1600-1400 rating or the 1500 rating.

  • 14 months ago


    jjpbetterboy, if your opponents rating changed 100 points that quickly, it seems like they fall in the category of new players. In the article, it mentions how their rating will change quickly because the system recognizes that there is a lot of uncertainty in their rating. However, your rating changes less when playing these opponents because of that same uncertainty.

    Also, the rating is based on the rating at the beginning of a game based on the fact that at the beginning of every game it tells you in the chat box exactly how much your rating will change for a win, draw, and loss.

  • 14 months ago


    play several games

    don't stop playing

    play people with a similar rating,

    and then all our ratings will be accurate enough!

  • 15 months ago


    I was wondering the same thing as you IvoryGambit. As I was in the process of losing to my opponent over a few weeks of a long game, his rating increased about 100 points. I would have liked to have known how he learned so much in that space of time, and maybe gotten some credit for his newfound skill.Wink

  • 15 months ago


    C.c.needs to explain whether one,s rating change post game is calculated on the basis of the opponent,s rating at the game start or end.There can be a considerable change in this over the course of a long game,significantly altering one,s own rating change,win or lose.

  • 15 months ago



  • 15 months ago


    I have just lost by checkmate my opponent was rated as 858 after the game his/her rating grew to 918 yet the game was 4 point loss to me so surely it should have been only a 4 point increase to the winner

  • 15 months ago


    Still doesn't explain how I can be challanged, make a move, and get 0 pts. on a resignation! What the heck! An early exit shouldn't be worth less points than a win and a draw should be worth something. It is the inferior system, having played both (USCF active in the '80s) that

    And really, would it kill you to add spell check to this site? I don't know anybody still in this situation...unless you want us all to look like English is our second language!

  • 15 months ago


    that was really useful

  • 16 months ago


    I don't like the rapid increase of RD with time of the Glicko ratings. When it comes to standard games, where people play a few times per week or month, ELO is superior and Glicko is a nuisance.

    Glicko is okay for blitz ratings, but chess.com please switch to ELO for standard chess!

  • 16 months ago


    I liked the explanation of the Glicko RD. I have a stats bakground but did not know what this term meant and thought as I saw it decrease it was telling me what an idiot I was. The explanation was good. Thank you.

  • 16 months ago


    Recently my rating is 1500+ . Let me inform how could I play upper level rating tournament!

  • 16 months ago


    Geremia -- Unless I've misunderstood, I think Elo ratings and Glicko ratings should be the same. The difference is in what factors are considered when calculating how to update ratings following a win or a defeat. Glicko aims to be more accurate than Elo but at the expense of extra book keeping (if we were trying to calculate by hand).

  • 16 months ago


    nikhil -- I've read debate about how to convert and there is disagreement about whether it's even possible since the ratings are figured against a completely different population of players. However, there does seem to me to be a consensus that c.c ratings are generous.

    If you want an easy answer then just substract 200 from your c.c rating to get an idea of what your FIDE rating might be. Just remember to take the conversion with a very large spoon of salt.

  • 16 months ago


    How could we convert (or approximate) Glicko ratings in terms of Elo rating?


  • 16 months ago


    if i had a rating of 1320 in Chess.com, would I have similar FIDE ratings?

  • 16 months ago


    A win is a win regardless of how you achieve it. The calculation for how much to adjust your rating following the win only cares about your relative ratings and how accurately those ratings can be estimated.

  • 16 months ago


    I don't know if I'm asking this on the right page but do you get more rating points by winning by checkmate over winning by resignation? Or is it the same, win is win?

  • 16 months ago


    The reason peoples FIDE rating is higher or lower than their Chess.com rating is because Chess.com uses Glicko and FIDE uses Elo, it clearly says that

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