Crossed the t’s, dotted the i’s

Although I made my 3rd GM norm last year in Balaguer, I did not have the 2500 FIDE rating to go along with it to complete the GM title. After that tournament, I was at 2484, and in my next two tournaments (the American Open and then the US Championship Qualifier), I managed to lose 1 rating point, so I went into Benasque at 2483.

During the tournament, I didn’t know how to exactly calculate the FIDE rating changes, as they have relatively recently gone from using a performance rating method to a game-by-game measure for rating changes. The only calculator available on the FIDE website does the rating change by performance rating.

It turns out there is a rating table on the FIDE website, at: that gives more exact values. Using this table, you can come very close to the exact rating changes that FIDE calculates.

The steps are pretty simple:

(0) Get your current FIDE rating and K-factor.

(1) Calculate the rating difference between your opponent’s rating and you, capped at 350 or -350

(2) Look in the One-Way table (under 10.1a) for the expected winning percentage (W_e) for your opponent based on the closest rating differential in the table.

(3) If you won the game, take W_e * K-factor.

If you drew the game, take W_e * K-factor.

If you lost the game, -1 * (1 – W_e) * K-factor.

This provides the game-by-game change, and essentially matches up with the exact changes for a whole tournament. Thus, for Benasque, after my draw with GM Gupta in the last round, this formula predicts my post-tournament rating would be 2499.6.

As the final crosstable shows, though, the actual change will be 16.9 points, so my post-tournament rating will be 2499.9. So after 10 games, the formula is off by 0.3 points.

Anyways, as FIDE rounds ratings up after 0.5, the 2499.9 gets rounded to 2500 and so I hit the rating threshold required to complete the GM title. It should be official in the next rating list (October 2008).

For what it’s worth, I also made a GM norm in Benasque with a 10-round performance rating of about 2622. Of course I don’t need the GM norm certificate, but since they prepared it, I took it along with me. I had made the norm after 9 games actually, as noted on Ajedrez ND.

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