ABSP Ratings System

The ratings system assigns a numerical rating to each player based on that player's performance at their most recent ABSP-rated tournaments.

For each tournament, a player is awarded Ratings Points. The Ratings Points for those tournaments are then combined using a formula to yield the player's ABSP rating. The formula is weighted, so that the most recent tournaments have a greater influence on the calculation. The various formulae involved, including the weighting calculation, are described below.

Higher ratings are better. The lowest possible rating is 50. The highest typical ratings are in the low 200s. The current ratings list is available on the ABSP database.

This ratings system was introduced at the start of 1999, following a decision made at the AGM in 1998. Useful information about all aspects of the ratings system, such as why we have one and how it came about, can be found in this helpful guide, compiled by the ABSP's ratings officer at the time, John Grayson.

Ratings Points

Each player is awarded Ratings Points at each ABSP-rated tournament in which they participate. The score is based on the player's initial rating; the opponents' ratings; and wins & losses only. It does not involve spread (points difference in the games). It also does not matter which opponents you beat - only the total number of wins and losses count.

Here is an example of Player X's record at the Penzance tournament:

Adding the ratings of all of the player's opponents gives 1901. The tournament rating is this figure plus 50 points for each game won, less 50 for each game lost, no change for each game tied; in this example 1901 + 350 - 250 = 2001 tournament rating points. This value and the number of games (12) are the input into the overall rating formula, described in the next section.

The tournament performance rating for the event is the average number of rating points per game, which is 2001/12 = 167 rounded. This number is displayed as the "Prf" value on the ABSP database's player profile for that tournament. (Aside: this is also the number you see displayed in the bottom left corner of a player's profile on the event's tsh Enhanced Scoreboard, if it has one)

Note: If players of markedly different ratings play (i.e. more than 40 points apart) then the rating difference is capped at 40. For example, if player X was rated 169 and played Player Y who was rated 125, then Player X would use 129 as her opponent's rating for calculating her own rating. Similarly, player Y would use 165 as his opponent's rating for calculating his own rating.

A further note is required in the instance of playing unrated players. They work out their rating from their first tournament in the manner described above. Their opponents then use that post-tournament rating to work out their own ratings points.

Finally, the effect of the lowest allowed rating, currently 50, is that the lowest allowed tournament performance rating is also 50. In other words, if the calculation of a performance is below 50, a value of 50 is used instead.

Overall ABSP Rating

The ratings calculation is based on the player's most recent 150* games and is computed based on the Ratings Points of the tournaments in which those games occurred. Any tournament whose games are all older than the games limit are discounted entirely for the purposes of this calculation.

For any tournament in which some games are within the limit and some are without, the Ratings Points for that tournament are reduced in direct proportion to the number of games that count.

If a player has played fewer than 150 games, the formula is unaffected, as demonstrated in the example later in this document. at the end of this file shows a calculation based on fewer than 150 games.

* the number of games that counted, and the weighting factors, were tweaked in 2011, as described in the footnote on the 2011 changes at the end of the document.

Before Penzance, Player X's games history was as follows (most recent first):

In the Weighted Rolling System, the games are weighted so that the more recent ones count more heavily. The weights used are 225 for the most recent game, down to 76 for the oldest game where the full quota of 150 games is available. The most recent tournament is the 22-game BMSC, and so these games would be weighted at 225, 224, ..., 204; this is an average weight (AW) of 214.5. Multiplying the rating points (RP) by the average weight (AW) gives the number of weighted rating points (WRP) for the tournament, which is 714928. The full list of calculations is shown in the table.

Player X's rating at this point would be 3,410,177 (sum of WRP) divided by the sum of the weightings (22,575), to give a rating of 151 rounded.

Now the Ratings Points from the Penzance tournament example above are added to the player's record:

As a result of adding the 12 games in the Penzance tournament, all the other tournaments now have a lower weighting than they had previously, and consequently the Weighted Rating Points value for each tournament is also lower, reflecting that they are not quite as influential as they were before.

* In order to restore the 150 game limit, the 12 oldest games from the Fishguard tournament need to be discarded from the calculation, leaving only 10 games. The Ratings Points are scaled in proportion to the number of games, so the original RP score of 3416 is multiplied by (10 / 22) to yield the 1552.

With all the changes applied, the new rating can be calculated exactly the same as before.

Player X's new rating would now be 3,447,656 divided by 22,575, which is 153 rounded.

Example with fewer than 150 games played

Finally, an example of the weightings used when a player has fewer than 150 games.

The same calculation (sum of the WRP column divided by the sum of weights) is used as for the previous examples.

The values here are 763980 divided by 5325 which is 143 rounded.

2011 change to the formulae

The description and examples above describe the ratings system as it is today. Prior to the start of 2011, the weightings and game count was different:

From the introduction of the new system until December 31st 2010, the calculation was based on each player's 100 most recent games, with weightings of 150 to 51. From January 1st 2011, the calculation uses 150 games, with weightings of 225 to 76.

Last updated: 25 January 2026