Why are Swiss Tournaments Often an Odd Number of Rounds?

[Ian Thompson]

Is there any truth to the last sentence of this statement about Swiss pairings?

"Players should be paired against players with the same number of points but the colour with which they play should also alternate. That is, a player who had White in the first round should have Black in the second round and White again in round three. However, these two principles often clash and that is the reason why almost all tournaments are played with an odd numbers of rounds."

which is then justified with:

"Of course, now some players will have one more game with White, while others have one more game with Black. But this is easier to tolerate than having two more games with Black which can easily happen in tournaments with an even number of rounds."

I'd always assumed that the reason Swiss tournaments are often an odd number of rounds is a hang over from all-play-all tournaments where you want an even number of players, so everyone has an opponent every round, which means an odd number of rounds.

[Roger de Coverly]

I'd always assumed that the reason Swiss tournaments are often an odd number of rounds is a hang over from all-play-all tournaments where you want an even number of players, so everyone has an opponent every round, which means an odd number of rounds.

The weekend tournament model as introduced by Stewart Reuben played six rounds, Friday evening, three on Saturday, two on Sunday. This however overlapped with earlier events like Ilford which were six player all play all sections and thus five rounds.

Later when the weekend tournament concept was well established, organisers cut back to five rounds, to eliminate either the Friday evening round or the Saturday evening one. It had the disadvantage over the six round events of not working so well with sections larger than 32 in theory, perhaps 48 in practice.

[David Sedgwick]

Pairing Reasons:

If everyone plays in every round, an odd number of rounds will give everyone a colour imbalance of 1. Most pairing systems prohibit an imbalance of 3.

An even number of rounds will give most players an imbalance of 0, but some an imbalance of 2.

Other Reasons:

As Roger says, 6 Round weekend tournaments have cut back to 5 Rounds. Causes: venue cost or unavailability, increased demand for byes on the third round of the day on Saturday evening.

A 7 Round event can be played Sunday to Saturday with travelling on the days before and after so only one working week.

A 9 Round event from Saturday to Sunday is also one working week, admittedly without travelling days, and is the minimum to be eligible for Title Norms.

[Nick Grey]

I liked 6 rounds over a bank holiday best. Plus old Surrey 7 Rounds Easter . I enjoyed 9 Rounds at the London Chess Classic in 2019 best. I think the earliest I'll play is 2021.

[Tim Harding]

David Sedgwick's response is pretty comprehensive, I think.
I would just add that we sometimes see 10-round events (e.g. Gibraltar and Reykjavik in recent years) which accommodate players who wish to take a half-point bye at some stage while still preserving norm possibilities.

In Ireland half-point byes are often allowed in weekend tournaments also since Saturday night games are unpopular with some people, and Sunday morning games with others. Also some people cannot play Friday evenings if travel is involved and they skip round 1 of a 6-round event.

Correspondence tournaments, where all games start together, usually do have an odd number of participants to balance the colours.

[Mike Gunn]

It's so all players can grumble about having an unequal number of whites and blacks.

[John Clarke]

Tournaments run on the jamboree system often for some reason had serious imbalances of colours. At the four-round 1970 BUCA teams event, I had three blacks and one of my team-mates four. There were doubtless several other examples.

[Paul Habershon]

Tournaments run on the jamboree system often for some reason had serious imbalances of colours. At the four-round 1970 BUCA teams event, I had three blacks and one of my team-mates four. There were doubtless several other examples.

Ah yes, jamborees! I remember a 1970s county internal schools event for teams of seven. Nine teams entered. Oops!