A tie-break for round-robin tournaments that counts only the points scored against the solid half of the table. Games against the tail are ignored entirely - what is left is the answer to one question: how did the player do against equals and betters? Below: the formula, the threshold explained, two worked examples from real events and a case where Koya and Sonneborn-Berger rank players in a different order.
Koya = the sum of points scored against opponents on 50% or more
The logic is simple. Points taken off the tail of the table come to everyone in roughly equal measure, and no tournament race is built on them. The real difference between contenders shows up in the games against the solid half, and those are exactly the games this tie-break counts.
Unlike Sonneborn-Berger, it does not matter which member of the solid half you beat: points against the leader and against the last player of that group weigh the same. The measure is blunter, but it is easy to explain to a player: this is what you took off the strong ones.
Like any tie-break, Koya is only compared between players on equal points. A high value on its own does not earn a place.
The threshold is measured from the maximum possible score in the tournament, that is, from the number of rounds. Half of that total is the line: everyone on that score or above joins the group of counted opponents.
Your own result does not enter this calculation: only the games against other players count. If a player made the solid half himself, that adds nothing - what matters is only how much he took off the rest of the group.
The same club round robin used to explain Sonneborn-Berger score. The threshold is 2½ points, and four players made the solid half. Three players shared second place on 2½ points - they are the ones to look at.
| Player | Points | Sonneborn-Berger | Koya | Counted |
|---|---|---|---|---|
| Pavel Grigoriev | 4 | 9 | 2½ | yes |
| Oleg Tarasov | 2½ | 6½ | 2 | yes |
| Darya Belova | 2½ | 5¼ | 1 | yes |
| Nikita Orlov | 2½ | 4¾ | ½ | yes |
| Maria Savelieva | 2 | 4 | 1 | no |
| Ivan Krylov | 1½ | 4½ | 1½ | no |
vs Pavel ½ + vs Darya 1 + vs Nikita ½
vs Pavel 0 + vs Oleg 0 + vs Nikita 1
vs Pavel 0 + vs Oleg ½ + vs Darya 0
Here Koya ranked the contenders exactly as Sonneborn-Berger did: Oleg first, then Darya, Nikita third. That happens often, and it is fine: both measure how well a player did against strong opposition, just in different ways. But agreement is not guaranteed - the next example is about precisely that.
Another event of the same size. Second place is shared by Roman and Timur, both on 2½ points. Sonneborn-Berger puts Roman higher, the Koya system puts Timur higher. Let us see where the difference comes from.
| Player | Points | Sonneborn-Berger | Koya | Counted |
|---|---|---|---|---|
| Alina Egorova | 3½ | 7¾ | 1½ | yes |
| Viktor Panov | 3½ | 7½ | 2 | yes |
| Roman Kovalev | 2½ | 6 | 1 | yes |
| Timur Aslanov | 2½ | 5¼ | 1½ | yes |
| Gleb Morozov | 2 | 3½ | 1 | no |
| Yulia Pakhomova | 1 | 3 | 1 | no |
Wins over Alina (3½) and Gleb (2)
A draw vs Yulia (1)
Wins over Roman (2½) and Yulia (1)
A draw vs Alina (3½)
Roman scored his points by beating the tournament leader and a tail-ender, while losing to the other two members of the solid half. Sonneborn-Berger does not notice that: it adds up the scores of the players you beat, and a big win over the leader outweighs everything else.
The Koya system looks only at the games inside the solid half, and there the picture is reversed: Timur has a point and a half against Roman's one. On top of that Timur beat Roman in their individual game - so on head-to-head he is higher as well.
The practical upshot: two of the three measures put Timur higher, one puts Roman higher. Who actually takes second place depends solely on the order in which the tie-breaks are listed in the tournament regulations. That is exactly why the list has to be announced before round one.
The 50 percent line is the default, not a dogma. The FIDE regulations provide for a modifier that moves it up or down in half-point steps. By raising the threshold the organiser narrows the group to stronger opponents; by lowering it he widens the group, adding the next band by score.
The Russian rules of the sport describe the same mechanism in a separate clause called the extended Koya system: the group of opponents is widened step by step by adding those who scored below half, or, conversely, narrowed by excluding those on exactly half and then on higher scores.
What it is for: the basic measure is fairly blunt and in short events often gives several players the same value. Shifting the threshold resolves that residual tie without moving on to the next tie-break. If a shift is used, it must be stated in the regulations alongside the tie-break itself - otherwise players will not be able to check the calculation.
The tie-break appears both in the FIDE regulations and in the Russian rules of the sport, but finding it there is not easy: the article numbers differ between sources, which is confusing.
The Koya system sits in article 9.2 under the name Koya System for Round Robin, abbreviated KS, in the same section as Sonneborn-Berger. The threshold shift is set out separately, in article 14.5 on modifiers.
Clause 38.3 defines the Koya system as the number of points scored against all opponents who scored 50 percent or more, including wins awarded through an opponent's penalty. The next clause, 38.3.1, describes the extended Koya system. The order of application for round robins is given in clause 39.3.1, where Koya closes the sequence.
The Russian rules reproduce the edition of the FIDE regulations that was in force until September 2023. There the Koya system stood in article 6.1 and the extended version in 6.2. After the regulations were revised the numbering changed, so references in Russian documents and in the current Handbook now point to different clauses while describing the same thing. If the tournament regulations cite an article, check which edition is meant.
The neighbouring tie-breaks have a known and documented origin. Buchholz is named after the German organiser who used the system in 1932. Sonneborn-Berger carries the names of William Sonneborn and Johann Berger, and its formula is linked to the work of Gelbfuhs and Neustadtl in the late nineteenth century.
The Koya system is different: neither the FIDE regulations nor encyclopedic sources say after whom or what it is named. In the documents it appears simply as the Koya System, with no author, country or year given. Theories about the name circulate online, but none can be backed by a source, so the honest answer is the plain one: the origin is unknown.
The Koya system is defined for round robins, where everyone plays everyone and the notion of a solid half has a direct meaning. In the Swiss system players meet only a fraction of the field, so using the tie-break there has to be written into the regulations separately.
In the sequence of tie-breaks Koya usually goes after Sonneborn-Berger: first the finer instrument, which tells apart the strength of each defeated opponent, and only then the blunter one. The Russian rules of the sport fix an order for round robins in which head-to-head and the number of wins are followed by Sonneborn-Berger, with Koya closing the sequence.
The full set of tie-breaks with formulas, articles of the regulations and an explanation of cut-offs is collected in the guide to chess tie-breaks, and ready-made sequences for a given format are in the article on which tie-breaks to choose for your tournament.
Support for this tie-break is patchy, and that is worth taking into account when choosing a platform.
The tie-break is on the list of available ones and appears in the standings columns once the organiser switches it on.
Some online services support several dozen tie-breaks, Koya among them.
Round-robin events use Sonneborn-Berger only. If that ties too, both players go through.
The platform does not run round robins at all - only Swiss and arena events.
Halve the number of rounds. An eight-player round robin has seven rounds, so the threshold is 3½ points.
Go down the final standings and mark everyone on that score or above. That is your group of counted opponents.
Take the games your player had against the marked opponents only and add up the points scored in them. A win gives one, a draw a half, a loss nothing.
Sonneborn-Berger for the same tournament takes longer to work out, so it is easier to check it in the calculator: fill in the crosstable and you get the scores, the tie-break and the places with a breakdown for every player.
In the Vibe Chess app a round robin builds its own round schedule from the entry list, keeps the standings live and calculates Sonneborn-Berger for players on equal points. A finished tournament exports as a TRF report - arbiter programs accept it and produce the remaining tie-breaks, the Koya system included.
It is a tie-break for round-robin tournaments. Only the points scored against opponents who themselves finished on 50 percent or better are counted. Games against the tail of the table are ignored entirely. The number answers one question: how did the player do against the solid half of the field?
Take the maximum possible score in the tournament, which is the number of rounds, and halve it. A six-player round robin has five rounds, so the threshold is 2½ points: everyone on that score or above joins the group of counted opponents.
Sonneborn-Berger weighs every result by the opponent's score: beating the leader is worth more than beating a mid-table player. Koya is blunter but more direct: an opponent either made the solid half or did not, and inside that group everyone is equal. That is why the two numbers sometimes rank players in a different order.
That cannot happen in a round robin: the total number of points is fixed, so somebody is bound to land on half or above. What is entirely possible is several players ending up with a Koya of zero: it means they took nothing at all off the solid half.
The tie-break is defined for round robins - that is written into its very name in the regulations. It does not appear in the recommended sequences for the Swiss system, where Buchholz is used in practice. The text contains no outright ban, so in theory an organiser may put it into the regulations for a Swiss event too, but then the calculation should be spelled out in detail.
Yes. The Russian rules state explicitly that when Sonneborn-Berger and Koya are calculated, unplayed games are treated as decisive, and a player left without an opponent is deemed to have won the game. The clause on the Koya system itself also names wins awarded through an opponent's penalty separately.
Usually after Sonneborn-Berger. The logic: first the finer measure, which tells strong opponents from weak ones, and only if it ties - the blunter one, which looks at the result against the top half.
Yes, the regulations allow a modifier that shifts the line up or down. That way the group of counted opponents can be narrowed to the strongest players or, on the contrary, widened. If such a shift is used, it must be stated in the tournament regulations alongside the tie-break itself.
The origin of the name is not described in any available source, unlike Buchholz and Sonneborn-Berger, whose authors and circumstances are both known. In the regulations it appears simply as the Koya System.
Yes, arbiter software and results services can display it if the organiser has put it on the list. Doing it by hand is simple too: mark everyone on half or more and add up your points against those players.
