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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


  • 4 years ago


  • 4 years ago


    Being check mated would mean lowering your rating !!  Reading the article on how chess Rating works' is advisable here!!

  • 4 years ago


    Rating points gained or lost are based on your rating at the beginning of the game.

    If you click on a member's name, look at their Online Chess profile or Live Chess profile and you can see their rating.

  • 4 years ago


    How can I see the rating of another member?

  • 4 years ago


    Does the rating adjustment depend on your rating and your opponent's rating at the start of the game?  Or at the end of the game?

  • 4 years ago


    SmileRoy777 has expounded a theory & formula based on income (personal?) vis-a-vis identifying environmental element methodology ! I think this is not based on the Law of Uniformity to be adhered in Chess.I  would be sorry, if this hurts my friend in chess.

  • 4 years ago


    Innocent I think our friend  Roy777,gin gin. Australia is on a bigger research on the subject since two months back. i dont know where is his stand now!! But I agree with you in so far as that  " no move no points" win.

  • 4 years ago


    If at least four moves have been made in a rated game, she will lose points and you will gain points if she times out.  If it's less than four moves and she times out, ratings will not be affected.

  • 4 years ago


    I am playing a game on here and my opponent refuses to make a move. It looks as if I have got very much the stronger position.

    My opponent doesn't want to lose any of her rating so she says she will simply let the game time out instead of resigning or making moves. If she moves I will be able to checkmate her very soon.

    How will my rating be affected if she lets the game time out?

    Will I gain any points?

    How will her rating be affected. Will she lose any points if she doesn't move and simply allows the game to time out?

    How does the rating system work in a case like this?

    (In her position she ought to resign because I will probably have her in checkmate in about 5 or 6 moves otherwise.)

  • 4 years ago



  • 4 years ago


    You want to quit because you're losing and don't want your rating to drop?!
    That's not very sporting of you. 

    "Anyway, I've played one French defense, and to my disappointment white played the exchange. I opened with a French again just recently, and white, on his third move took on d5 again! Uhhgg. I asked in another forum if I could abort, and it seems like I can not, but 2 people answered that I should resign as it would NOT be rated since only 3 moves were made. (2 by black, 3 by white.) My time is running out, and I will play if I need to. But if I let the time run out, or if I resign and the game is not counted, I would opt for that and start a new game. I'm glad I was referred to this specific forum, where I can hopefully get a definitive answer to my "abort" question in some "general issues forum". Thank you in advance for your answer."

  • 4 years ago


    I just joined chess.com. I do not consider myself a beginner but not sure how i fit. Any suggestions who i can play? Are all games timed?
  • 4 years ago


    thanks for good clear concise explanation... nice to know that whether its in-depth nerd material or simple explanation, doesn't change the fact that overall i still suck at chess compared to most other players- still love to play it though Laughing

  • 4 years ago


    Thanks much for the clarification. A lot of us have been wondering and have apparently missed wherever that was announced.

  • 4 years ago


    All new members now start off as "unrated" although they are still technically rated 1200.  As soon as they finish their first rated game, their ratings will update.  

    The same goes for current members who show "unrated".  When they finish their next rated game, their ratings will display the actual number.  There's no difference in playing an "unrated" player as a member who's ratings are visible.  

  • 4 years ago


    How do I change my stats to a rated player instad of unrated player

  • 4 years ago


    I am playing an "unrated" opponent but the "details" says it

    is in fact a "rated" game. How is my rating affected if I win

    or lose?  Thanks all you chess afficianados!


  • 4 years ago


    What are your opponents' ratings?

  • 4 years ago


    i play many games

    and i most of that games win

    of 16 games i win 14

    but rating isnt higher when i win

    rating is always 1170

    or i win or lose rating is 1170!!!!!!!

    what i must do

    i play tournament

    and rating is 1000-1170

    maybe for that rating is always 1170

    pls help?

  • 4 years ago


    CoolHi hgreen! Yes ,you get rated when your opponent's time run out!!!
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