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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


  • 16 months ago


    Like most games that humans play there are multiple variables that make up scores in various systems. Only a few of the variables are know widely at a certain period in time, thus with an increase in the global human population over time more variables will develope that become widely know and scores will change until chimps are introduced to the game -then we will need to refigure....Bobstem  

  • 18 months ago


    my rating is not fine, because play few games.

  • 19 months ago


    I looked at the The Glicko System paper and the comments to this article, and found the rating system on Chess.com has yet to be explained, especially the several variables and implementation tweaks which the Glicko paper left to administrative discretion.  Until the code is dumped online as open source, it is a hackers secret formula, hardly nearing the ethical standards hoped for in a good sportsman like rating system, and thus a big negative in comparison to other chess competition sites.

  • 20 months ago



       Everbody has multiple ratings based on the time duration of the game. Your standard rating is 799, your blitz rating is 633 and your bullet rating is 559. Maybe, you are confusing your blitz and standard rating. Just go to your home page and scroll down a bit and the list of ratings is on the right. You should see 3 ratings that start with the phrase "Live Chess". The y are Blitz, Standard and Bullet in that order.

  • 20 months ago


    Sometimes when I log onto live chess after taking a break of a few hours my rating drops signifigantly! last night i won a number of matches in a row and was at 799 this mourning im back to 636! i haven't been able to break the 800's because every time i do the next day im back at the 600's! is this normal? and if so why does the rating system do this?

  • 20 months ago


    It happened several times. I was playing white and it was the opponent's turn. I made a move and waited for him to play. All of a sudden the game stopped and I got a msg black won. WHY????? 

  • 20 months ago


    Just because I was interested, I found this discussion:

    Rating Point Option on Timeout Wins

    Part way down the discussion, TadDude says: "Timeouts where there are less than three and a half moves do not impact rating in any type of game."

  • 20 months ago


    No, it's not your imagination and neither is it a bug. It depends on how many moves are made in the game before the timeout. I can't remember exactly but I believe you need to have made at least 4 or 5 moves for the rating to change...

    So, obviously your rating won't change if your opponent times out without any moves for example.

  • 20 months ago


    That's a good question. Recently, I've been noticing that my rating hasn't been changing when certain opponents timeout. I don't know if it's something to do with timeouts not counting if the opponent is still at the "Unrated" stage or whether it's a bug or whether it's just my imagination.

  • 20 months ago


    Will a win by checkmate increase my rating more than a win because my opponent runs out of time?

  • 20 months ago


    That's impossible.

  • 20 months ago


    I won a game and lost 300 elo is this a bug?

  • 21 months ago


    One problem with the rating system is this: I often sit in the evening playing online chess in the bar drinking beer. At the beginning of the evening I will probably be playing close to my best. By the end of the evening I will be making the most elementary blunders!

  • 21 months ago


    What is the calculation at the begining which came to 150?

  • 22 months ago


    I just read the glicko system article and can see why it would be difficult to do by hand!

  • 23 months ago


    I don't understand any rating system and I don't want to.  I just want to know that there is one and that everyone I am playing is on the same rating system.  I wish this site used a system that was more used world wide, but it sounds like this one may end up being one that is.  I haven't played very many games here, but my rating is around what it was on another site where I played many games.  In a nutshell, if you beat someone that sucks its not as big a win as it you beat someone good, and vice verse with losses.  Having the same number of points for a winning game is rather stupid, since beating someone better should be worth more than beating a lesser player.  After all, you don't get the same sense of accomplishment when you beat a 3 year old in a foot race (assuming your at least a teenager or adult) versus beating a current Olympic Gold Medalist Sprinter.  If you do you are quite sad.  ENJOY CHESS!

  • 23 months ago


    @ krunalgohil19 okay..i will try that..cheers ! :)

  • 23 months ago


    @nen:go to live chess

  • 23 months ago


  • 23 months ago


    Thanks CharlesRoberson , I just checked rated and unrated games, most were unrated, so I know now why my rating was not moving.

    Thanks a lot for the answer.

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