Sonneborn–Berger score

The Sonneborn–Berger score (or the Neustadtl score) is a scoring system often used to break ties in chess tournaments. It is computed by summing the conventional score of each defeated opponent, and half the conventional score of each drawn opponent.

Neustadtl score is named after Hermann Neustadtl, who proposed it in a letter published in Chess Monthly in 1882. A similar scoring system was first proposed by Oscar Gelbfuhs in 1873, to be used as a weighted score in place of the raw score; his system was also designed to work for tournaments where not everyone had played the same number of games. The scoring system is often called the Sonneborn–Berger score, though this is something of a misnomer, since William Sonneborn and Johann Berger were advocates of a variant now known as the non-Neustadtl Sonneborn-Berger score, which added in the square of the raw score of each player.

Both the Gelbfuhs and the non-Neustadtl Sonneborn-Berger score provide a full weighted score to replace the raw score, but this is not needed for breaking ties between players with conventional scoring. As a result, it is the Neustadtl Sonneborn-Berger score that is in common use for tiebreaks in modern chess.

Other common tiebreaking methods in chess tournaments include the head-to-head score, the Koya score, or favoring the player with the most wins (or black games). In Swiss system events, comparison of the Buchholz scores and the sum of progressive scores are common.