Tournaments / Swiss system

How the Swiss system works

A Swiss tournament lets a large group play a few rounds and still produce a fair winner. Nobody is knocked out, and after every round you are paired with someone on your own score.

The idea

In a knockout, half the players go home after one round. In a round robin, everyone plays everyone, which takes as many rounds as there are players. The Swiss system sits between the two: everybody plays every round, and each round pairs you with someone who has done as well as you have so far. After a handful of rounds the players at the top have beaten the other contenders, and the player with the most points wins.

How a round is paired

1. Players are sorted by score, then by rating.
2. They are grouped by score: everyone on 2 points together, everyone on 1½ together, and so on.
3. Inside a group, the top half plays the bottom half: in a group of eight, 1 plays 5, 2 plays 6, and so on.
4. Two players never meet twice. When a group cannot be paired without a rematch, somebody moves down to the next group.
5. Colours are evened out: nobody gets White or Black three times running, and nobody ends up more than two games apart.
6. Late in a long event with few players there is sometimes no pairing left that keeps all of this. The system then picks the least bad one and says what it had to break, rather than refusing to pair the round.

The first round is the exception: nobody has a score yet, so the field is split in half by rating and the top half plays the bottom half.

How many rounds

Enough that the leader has had to beat the other contenders. The usual guide is the number of times you can halve the field, plus two:

Fewer rounds and several players finish level; many more and you run out of fresh opponents.

The bye

With an odd number of players, one person sits each round out and gets a full point. It goes to the lowest-placed player who has not already had one, so it travels down the table rather than landing on the same person twice.

A bye is not a game, which matters for the tie-breaks. If an unplayed round counted as an opponent on zero, taking the bye would wreck your Buchholz through no fault of your own. Instead it counts against a virtual opponent: someone who had your score going into that round and then drew every round after it. That is the FIDE rule, and it is what this site uses.

Tie-breaks

Players finish level on points all the time, so you decide beforehand what separates them. The common ones, strongest first for most clubs:

• Direct encounter. If the tied players all played each other, their score against each other decides. Simple and easy to explain, but it only applies when they have all met.
• Buchholz cut 1. Add up your opponents' scores and drop the lowest one. It rewards whoever had the harder draw, and dropping the weakest opponent takes out the biggest piece of luck.
• Buchholz total. The same without dropping anything.
• Sonneborn-Berger. The full score of everyone you beat, plus half the score of everyone you drew. It cares about who you beat, not only who you played.
• Number of wins. Rewards playing for a result rather than drawing.

Say which order you are using before the first round, and put it where players can see it.

Running it on the night

1. Collect the names before you start. A player who arrives after round one can be added, but they miss that round.
2. Pair the round and put the list where everyone can see it, or share the link.
3. Enter each result as the game finishes rather than all at once at the end.
4. Pair the next round only when the last result is in: the pairings depend on the scores.
5. If somebody has to leave, mark them as withdrawn. Their games stand, and they are left out of the next pairing.

Round robin instead

With about ten players or fewer and enough time, a round robin is fairer: everyone plays everyone, so nobody can complain about the draw. It takes one round fewer than there are players, or the same number when the field is odd, since one person sits out each round.