Juha Kivijärvi chess

Performance calculator

Average rating of opponents:
Performance rating by game:
Performance rating (FIDE) :
Performance rating (linear):


As far as I can see, the reason the latter two formulas are used is the ease of calculation. The first one practically requires a computer, the second one is manageable with a calculator and a printout of the rating difference table, and the third one doesn't even need the table. FIDE performances are usually fairly close to the proper ones when the dispersion of opponents' ratings is small. However, the FIDE formula doesn't handle outliers well and a win against a weak opponent may very well even decrease the FIDE performance. The linear formula is near to the FIDE formula when the score is close enough to 50%.

When a player wins or loses all the games, performance rating is undefined. FIDE has solved this by choosing somewhat arbitrarily 800 points as the rating difference of an extreme result, whereas the linear formula gives 400 points. In these cases it would be pretty much equally justifiable to declare any other sufficiently high number as the performance rating. The performance of a maximal score is definitely higher than the performance when half a point has been lost, but that's it.