The round-robin system: how it works

Both numbers are fixed the moment you know the field, which is the system's main practical advantage: the whole schedule is known before the first move.

With an even field: N − 1 rounds. With an odd field: N rounds, because somebody sits out each time - the empty place in the schedule acts as a virtual opponent - how byes work.

Total games are N × (N − 1) / 2. That number grows fast, and it is what limits the format: twelve players is sixty-six games, which is a weekend rather than an evening.

Nobody works out a round robin by hand. The pairings follow a standard rotation - one player stays in place while the rest revolve - and the resulting tables have been published for over a century.

• The schedule is fixed in advance. Results do not affect it, so every round can be published before the event starts.
• Players draw numbers, not opponents. A player gets a number at the start, and the number determines every game they will play.
• The tables are standard. Ready-made ones exist for every field size - the Berger tables.
• Software does it anyway. Any tournament tool generates the whole event at once.

A consequence worth using: because the schedule is known, you can print it, hand it out and let players see exactly when they play - something a Swiss can never offer.

In a round robin the pairings are fixed, so the only freedom left is colour - and the standard tables handle it.

• Colours alternate as evenly as the arithmetic allows. Over an odd number of rounds perfect balance is impossible, so somebody gets one extra White.
• The imbalance is known in advance. Which is fairer than it sounds: it is visible before anybody plays, rather than emerging from results.
• A double round robin removes it entirely. Every pair meets twice, once with each colour - about double round robins.
• Do not reassign colours by hand. Adjusting one pairing breaks the balance of several others - the tables are a system, not a list.

Points first, as everywhere. What differs is the tie-break - and using the wrong one here is a common and consequential error.

The correct tie-break for a round robin is Sonneborn-Berger: the sum of the scores of opponents you beat, plus half the scores of those you drew with. It weights your points by whom you took them from - how it is calculated.

After that: direct encounter between the tied players, then number of wins. State the order in the regulations before the event - tie-breaks generally.

The practical rule: under twelve players, round robin; above that, Swiss. And there is a case organizers underuse - a turnout half the size you expected. Switching to a round robin on the spot turns a thin evening into a proper tournament - choosing between them.

• Watch the length. Ten players is nine rounds - a full day at rapid, not an evening. Count before promising a finishing time - schedule arithmetic.
• Withdrawals hurt more than in a Swiss. Somebody leaving halfway distorts every remaining pairing's tie-break. Decide in advance how unplayed games are scored.
• Publish the whole schedule. Players can plan their evening, and latecomers know exactly which round they are missing.
• Avoid it with mixed strength. A beginner in a round robin with club players loses every single game - which is the fastest way to lose that person - about retention.
• Use it for a club championship. With eight to ten regulars over several weeks it is the fairest format there is, and the standings stay interesting to the last round.