Sheffield & District Chess Association

Established 1883







Developments in the ECF Rating System


a)  Swathes of Players Becoming Unrated


Some players, especially those who have not yet resumed over-the-board chess since the original cessation caused by Covid, noticed in May or before that they no longer had a current ECF rating.  On the ECF rating database inquiry screen, which differentiates between “Rated” and “Unrated” players, these players had been cast into the abyss of the undead, i. e. the “Unrated” list.  As most had been out of action for less than the traditional three years period of grace, some evidently were a bit grumpy about this turn of events.


This may have been in part due to the introduction of a system of rating categories, which hitherto had been absent, being later than planned.  (At this point the reader should visualise the cavalry beginning to appear over the horizon.)


b)  Introduction of Grading Categories


In the old 3-digit grading system, each person’s grade had affixed to the end a letter, A, B, C, D or E, and later sometimes X.  This letter encapsulated a combination of how many games contributes to the grade and how long ago they were played.  Essentially A grades were likely to be more accurate than B grades, which in turn were probably more accurate than C grades and so on.


In the new 4-digit rating system there are 4 categories, A, K, P and H, and most of the post-Covid non-returners will find they are now in category K or category H, according to circumstances.


So, what do these category affixes mean?  To understand this, it helps to understand that two different rating calculation methods (“algorithms”) are used as the circumstances require.  Most calculations follow the Elo-style approach in which, broadly, the difference between the two opponents’ ratings is used to determine an amount to be added or subtracted to a player’s rating as it was at the start of the game, giving a new rating which will feed into the next game.  This method is called the “K rating algorithm”, and yes, there is a link there to the K category suffix.


For players without a rating, a calculation method is used which does not include a player’s previous rating. This very much resembles the recursive method use by graders of old in producing an “estimated” grade for an ungraded player before doing the main calculation run.  (Recursive methods produced an “estimated” initial grade for an ungraded player which was the same as the final grade calculated for that player, “proving” the estimate was “correct”.)   This method is called the “P rating algorithm”, and yes, there is a link there to the P category suffix.


Meanings of the categories:


A category is ascribed to players whose rating has been calculated by the K rating algorithm, and who have at least 30 games included from the previous 12 months - essentially the same as for an old-style A grade.


K category is ascribed to players whose rating has been calculated by the K rating algorithm, but who have less than 30 games included from the previous 12 months and at least 10 games – much like the old-style B, C and D grades, though without the graduated degrees of “accuracy”.  (There could have been new K, L and M categories on a similar basis as for B, C and D.)


P category is ascribed to players whose rating has been calculated by the P rating algorithm, and who have less than 10 rated games in the system.  The “P” actually stands for “partial”, but it could perhaps more usefully be thought of as standing for “provisional”.  If after a rating calculation a player who had a P grade has then got 10 or more rated games in the system, they acquire a K grade, or if they had played 21 or more rated games in the last month (very, very unlikely) they would get an A grade.


H category is ascribed to players who “have limited recent activity under many different circumstances.”  The “H” stands for “historic”.  If a player with an H rating has at least one game rated in the next 12 months then their rating with become a K rating, but on the other hand a further 12 months of dormancy will result in them becoming “unrated”.  Thus the H category seems only a temporary one, leaving just A, K and P being used in the long term.


When an unrated player who has had a rating in the past eventually returns to being rated, they are to be treated as a “new” player for the purposes of rating calculation, and so will initially be rated using the P algorithm.


A and K ratings are regarded as “full ratings” and are regarded as fully fit for normal use.


P and H ratings are regarded as “partial ratings”.  The accuracy of P and H grades in terms of a player’s present strength is unquantifiable, and they can only be an approximate “ballpark” guide and are best taken along with any known recent results which as yet have not been rated.


Details of ECF rating calculation (though not yet including references to categories) can be found on the ECF rating website at