Tie-break systems are used in chess Swiss system tournaments to break ties between players who have the same total number of points after the last round. This is needed when prizes are indivisible, such as an official "champion", trophies, or qualification for another tournament. Otherwise players often share the tied spots, with cash prizes being divided equally among the tied players.If the players are still tied after one tie-break system is used, another system is used, and so on, until the tie is broken. Most of the methods are numerical methods based on the games that have already been played or other objective factors, while some methods require additional games to be played, etc. Strength of schedule is the idea behind the methods based on the games already played: that the player that played the harder competition to achieve the same number of points should be ranked higher.
Harry Golombek points out deficiencies in most of the tie-break systems and recommends a playoff if there is time. If not, he recommends Sonneborn-Berger and then the player who has the most wins. For Swiss tournaments, he recommends the Buchholz system and the Cumulative system (Golombek 1977:322).
For Swiss chess tournaments for individuals (not teams), FIDE recommends - in an Annex to the FIDE Tournament Regulations regarding tiebreaks:
Read main article: Buchholz system
The Median system is also known as the Harkness System, after its inventor Kenneth Harkness. For each player, this system sums the number of points earned by the player's opponents, but discarding the highest and lowest. If there are nine or more rounds, the top two and bottom two scores are discarded. Unplayed games by the opponents count ½ point. Unplayed games by the player count zero points. This is also known as the Median-Buchholz System (Just & Burg 2003:199-200).
The Modified Median system is similar to the Median system, except:
This system is the same as the Median system, except that no scores are discarded (Just & Burg 2003:200). Ephraim Solkoff did not invent this system. He introduced it to the United States in 1950, but it was used in England prior to that (Harkness 1967:138).
To calculate this, sum the running score for each round. For example, if a player has (in order) a win, loss, win, draw, and a loss; his round-by-round score will be 1, 1, 2, 2½, 2½. The sum of these numbers is 9. This system places more weight on games won in the early rounds and the least weight on games won in the final rounds. The rationale for this system is that a player who scored well early in the tournament has most likely faced tougher opponents in later rounds and should therefore be favored over a player who scored poorly in the start before subsequently scoring points against weaker opponents (Just & Burg 2003:200-201).
This sums the cumulative scores of the player's opponents (Just & Burg 2003:202).
If the tied players played each other, if one of them won then he finishes higher on tie-break (Just & Burg 2003:201).
The player that had the black pieces the most times finishes highest on tie-breaks (Just & Burg 2003:201).
The player with the most wins finishes highest on tie-breaks. This is used as the first tie-break rule for individual tournaments in ICCF.
Invented by Isaac Kashdan, this system awards four points for a win, two points for a draw, one point for a loss, and none for an unplayed game. As a result, if players with no unplayed games tie, the one with fewer draws finishes higher on the tie-break (i.e. a win and a loss is better than two draws) (Just & Burg 2003:201).
Read main article: Sonneborn-Berger score
Add the scores of every opponent the player beats and half of the score of every opponent the player draws (Just & Burg 2003:201). The system was named after William Sonneborn and Johann Berger, but it was invented by Oscar Gelbfuhs (Harkness 1967:137). The system is the main tie-breaking system in round robin tournaments, but is also used in Swiss tournaments. It is also called the Neustadtl score.
What we call the Sonneborn-Berger system was not invented by Sonneborn or Berger, and it was not originally designed for tie-breaking. It was invented by Oscar Gelbfuhs about 1873 to be used as a weighted score in round-robin tournaments. It would be used instead of the raw score for final places. In 1886 Sonneborn criticized the system and suggested an improvement that would give a better weighted score. His suggestion was to add the square of the player's points to the amount calculated as above. In 1887 and 1888 Berger studied Gelbfuhs' system and the suggestion of Sonneborn. This improvement became known as the Sonneborn-Berger system.
When the system is used to break ties between equally scoring players, adding in the square of the player's raw score does no good, so the Sonneborn improvement is omitted. However, the system has retained the Sonneborn-Berger name (Harkness 1967:136-37).
This method uses the average performance rating of the player's opponents. The "performance rating" of a player is basically the rating he would receive if he had started the tournament without a rating (Just & Burg 2003:202).
The average rating of the player's opponents (Just & Burg 2003:202).
Among tied players, the player whose first loss came last gets priority. If player A’s first loss was in round 4 and player B’s first loss was in round 2, player A gets priority. This was a tiebreaker used by POP in 2004-2005.
If a player arrives after the first round is paired, the player loses priority. This tiebreaker is currently used by POP.
FIDE rules provide for a single fast decisive game. Black gets five minutes on the clock whereas White gets six minutes but must win (i.e. a draw counts as a win for Black). The player who wins the draw of lots may choose which color he wants.
As a last resort, ties are broken by a random process such as a coin flip (Just & Burg 2003:203).
The U.S. Chess Federation (USCF) recommends these as the first four tie-breaking methods to be used: (Just & Burg 2003:199)