How Swiss pairing works

Round one is the only one drawn in advance

Round one is paired at random, or by seed if you have one. Every round after it is paired from the standings as they stand when the previous round finishes — which means it cannot be drawn in advance, because it depends on results that have not happened.

This is the property that makes Swiss work and the one that trips people up: you cannot publish the whole schedule on the morning of the tournament. You can publish round one and the number of rounds, and that is it.

A worked example: eight players, three rounds

Round one pairs the eight at random. Four win and four lose.

Round two pairs the four winners against each other and the four losers against each other. After it there are two players on 2–0, four on 1–1, and two on 0–2.

Round three pairs within those groups: the two unbeaten play each other, the four on 1–1 pair off, and the two winless play each other. After three rounds exactly one player can be 3–0, which is the point — that is why three rounds is the right number for eight players.

Nobody has been eliminated. Everybody has played three matches. The table is ordered by points, and the tiebreakers sort out the players who finished level.

Rematches, and what happens when it runs out

The pairing avoids putting two players together twice. On a small field over a long tournament it will eventually run out of fresh opponents at the right score, and at that point it has to either pair somebody against a different score or repeat a meeting.

Neither is wrong — it is what happens when a Swiss runs long against a small field — but it should be surfaced rather than silently done. Whistle.day reports a rematch when it has to make one.

Byes score a point

An odd field means one player sits out each round. In a Swiss that bye takes the points for a win, which surprises people who are used to brackets, where a bye scores nothing and is simply a free pass.

The reason is that a Swiss bye is a lost opportunity to gain points. Scoring it zero would send whoever happened to be the odd one out to the bottom of the table for something they had no part in. In a bracket the same record means the opposite thing — the round itself, skipped — so it scores nothing. Same word, opposite meaning, which is worth knowing if you ever look at the underlying data.

What Swiss is good for

Fields too big for a round robin and too valuable to knock out. Thirty-two teams playing everyone-plays-everyone is 496 matches, which is not a day. Thirty-two teams in a straight knockout means sixteen of them have finished by mid-morning. Five Swiss rounds gives all thirty-two the same five matches and produces a credible order.

It is weakest when you need a definitive winner: a Swiss table can leave two players level at the top on every tiebreaker you have. That is why most Swiss tournaments finish with a small playoff.

Common questions