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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


  • 17 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

  • 17 months ago


    No idea about the details, jHaygood. As far as I can gather, "Unrated" is what you get when the site has so little recent data on you that it can't be sure how good you are. Even so, it will still make a whimsical guess. In the case of totally new accounts, they start at 1200. In your case it's probably something else but the uncertainty on that is too large for the site to be willing to tell you what it is.

    Basically, it has no idea whether you've spent the last year holding your own against GMs or spent it holding yourself up against a lamp post after too many stiff drinks.

  • 17 months ago


    Question:  The site says that I'm 'Unrated' ...I played on this site a few years ago and recently started playing again...I lost my first game so the 'Unrated' status is warranted...However, I've read in an on site forum that players start at 1200 ...Does anyone know why I'm 'Unrated' or why I didn't start with 1200 as I've read?

  • 17 months ago


    I have been about to win several games, and then one move away from checkmate the opponent resigns!  How does this affect my final score?  

    What if I am 2 moves away from checkmate, and their only way to block the check they are in is to block it with their queen, and in my next move I am going to take their queen and put them in checkmate, but they resign instead of moving their queen to block the check, will this affect my rating differently than if I had taken their queen and won with a checkmate and are pieces you take accounted for in the ratings?

  • 18 months ago


    I played a game and won. my rating increased by 0.00.

    I think, I shouldn't be worrying about rating here.

    I just play and enjoy.

  • 18 months ago


    Point if fact, I know people with Chess.com ratings 300 points higher than their USCF rating and I know people with Chess.com ratings 200 points lower than their USCF ratings.

  • 18 months ago


    USCF and FIDE ratings don't really have a correlation to Chess.com ratings or any other server ratings. The Chess.com system isn't even the same mathematical system, however it is similar. Also, there is a key difference in how ratings are acheived. To get a FIDE or USCF rating, you enter a tournament and have zero control over whom you play. Online servers offer more control. 

    This extra control means that some people may have higher Chess.com ratings than another person with the same USCF rating. One might just send out a seek to people of higher strength, while the other might only challenge those 200 points weaker than he/she. That will produce noticable differences in their online ratings. 

  • 18 months ago



  • 18 months ago


  • 18 months ago


    good explanation......before reading dis my mind was very much confused abt this rating system

  • 19 months ago


    How do Chess.com ratings compore to USCF Ratings and FIDE ratings? If my USCF is 1600, should I expect my Chess.com rating to be about the same?

  • 19 months ago


    Thank you so much I was really confused on how the ratings work now I know I also had no idea what FIDE was or ELO now I know thanks a lot!

  • 19 months ago


  • 19 months ago


    How would you rate my rating which is 652 so far? I want your feedback. I do not know where I am currently standing? I have started playing it online 5 days ago.

  • 19 months ago


    good article, and I found the comment/questions/ et al. to be interesting and amusing as well

  • 20 months ago


    VERY helpful

  • 20 months ago


    Nobody should expect ratings to predict outcomes very closely. Even the "TRUE rating" couldn't determine the outcome.

    In order to find out my "TRUE rating" here's what I imagine I would have to do:

    a) Assemble a whole bunch of test positions, with evaluation for how good or bad various moves would be, and evaluation for how long I take to solve them

    b) Test myself in various conditions against the problems. This is complicated because I might be bad at endgames if the room is noisy, or great at openings if the room has flickering lights etc.  

    c) Take some average of the results (who decides what factors are weighted by how much?)

    It would take a lot of energy to carefully measure the "TRUE rating".

    Then I get to an actual contest, and the outcome depends on my "TRUE abilities" + my actual state that day (compared to my average) + the actual conditions that day (random input from the environment) + the moves my actual opponents choose.

    In the ratings system, all that noise is condensed into results (0, 1/2, 1) and then further condensed into the ratings adjustment to go from the current estimate to the updated estimate.  

    Overall there's a lot of condensation that occurs.

    The "TRUE rating" doesn't determine the outcome. A person's mental & physical state, and the particulars of the setting and the actual game are what determine the outcome.

    If chess had gambling, there could be a public "weigh-in", or like what they do in horse racing, where the contestants would show off their form before the betting closed ...

  • 20 months ago


    It's like on the street. You gotta mug a lot of people who got more n wot you hav but it ain't always easy. Best to catch em drunk....

  • 21 months ago


    where i can see my rating before start a new game

  • 21 months ago


    I have read the first 20 comments that appeared when I logged into this area.  There a lot of very interesting questions posed but no answeres!  I suspect the answeres to these questions would be not only interesting but, in some cases, educational.  If you are not going to provide replies to inquires this forum is of little value except as a "gripe" or "brag" forum.  Discontinue it and save yourself some computer space.

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