# Chess Ratings - How They Work

• erik
• | Aug 23, 2007
• | 198356 views

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.

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):

• 20 months ago

Thanks.  I guess I am incorrect.

• 20 months ago

@pfred42: suppose a new player with real rating about 1600 joins the site and starts 10 games against established players with 1200 rating. If I recall correctly, the first win will add some 150 rating points.  If this happened in all games, the new player would be now rated at 1200+10*150 = 2700.

Hence the reason for always using the rating at the end.

USCF does the same thing, BTW; the ratings are computed iteratively with pre-tournament ratings being only a starting point, then replaced with new proposed rating, then again, until they converge and change no more. At that point, the final post-tournament result are consistent with each other.

• 20 months ago

as far as I can tell, points are calculated at the end of the game,  and are base on the difference from your own rating. example above if a player has the same rating as you, you get 7 points for a win.  if he has less ranking than you, you get less points  and if he has better ranking than you,  you get more.  now if you have for example 1500 and you play a player with 1600, you can get 9 or 10 points,  but if the same player lose many games due to time, you may only get one point because his ranking may be down to 1300 by the time he lose with you.

• 20 months ago

I guess I would disagree.  I would think at the beginning because that is the basis by which one chooses an opponent.  For most players who have been around awhile the change would be small in the short period of time and same for newcomers as they would not have been likely to complete that many other (online) games in that same interval.  For example, I chose an about-equally rated opponent back in January (online game still in progress) whose rating has dropped because he "timed-out" on several games--didn't really lose competitively.

• 20 months ago

Ophunky is incorrect.

Rating at the end is always more reliable than at the beginning.  It would make no sense to use the one at start.

• 20 months ago

Go down 2 from there to ohpunky81, 2nd paragraph.  Says beginning.  Perhaps chess.com can tell us.

• 20 months ago

@pfred42 -- look 9 posts down from yours for the answer.

• 20 months ago

Thanks for the reply.  But from other posts I read it sounds like the points for W/L/D are set by the opponents' (and your own for them) rating at the date you start.  Is that true or are the points a moving value as you play?

• 20 months ago

yes, you get the same amount of points, no difference.  only problem when is you win due to time and your opponent was playing 50 games. his rating would decrease very fast and you probably would not get that many points.

• 20 months ago

Are the points one gets for a win the same whether the win is by mate, resignation or time?

• 21 months ago

Guru_2, i´ve seen that depends of the rating of your opponent, if you play and win against a player with a higher rating than yours you will get very good points, but if you lose you won´t lose much; the other is, if you play and lose against a player with a lower rating than yours you will lose a lot of points, but if you win you´ll get a few points. It must be a tab in some place, i´ll try to find it and share ...

• 21 months ago

Potential changes to rating are stated in the chat box at the beginning of each game. It's the line that says, "win +8, draw 0, loss -8" or something similar.

• 21 months ago

Guru_2,you have played many blitz games.Your strength seems fairly constant,so you only gain /lose 2 pts or so per win/loss.

Don't think of ratings as a measure of your worth as a human being!

They are a tool to ensure you get a good match with a fairly equal opponent

• 21 months ago

Please help in understanding, how many points will be acquired or deducted in case of win or a loss respectively? ( In 10!0 game)

• 21 months ago

thanks.

• 21 months ago

@spanishfly25  - at the end

• 21 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.

• 21 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.

• 21 months ago

play several games

don't stop playing

play people with a similar rating,

and then all our ratings will be accurate enough!

• 22 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.