Before Brazil's runoff, traders split on Flávio Bolsonaro winning by under 4 or 4–8 points

On the eve of Brazil's presidential runoff, traders see a close race and are almost evenly split on how large a win by Flávio Bolsonaro would be. A victory by 4 to 8 percentage points is, by a hair, the likeliest single outcome, with a win by less than 4 points just behind it. Neither is better than unlikely on its own, because the two together share most of the expectation.

Other outcomes sit well back. A Bolsonaro win by 8 to 12 points or by 12 or more is a long shot. A narrow win by Lula, by less than 4 points, is unlikely. The 4-to-8-point outcome counts only if Bolsonaro finishes first by that margin in the share of valid votes, as the official count shows.

The path to this point has been bumpy. In the first days after tracking began, a Bolsonaro win by 4 to 8 points looked close to a toss-up, helped by an Ipespe/Abrapel poll that put him 5.4 points ahead. Expectations then fell sharply on October 13 and 14 and kept sliding into the weekend. After a dip on October 19, they jumped the next day, then eased through midweek. On Saturday they rose again to their highest since the opening days.

The polls explain why the race looks tight. Two surveys released October 19 showed much narrower leads for Bolsonaro: 50.3% to 49.7% in Nexus/BTG and 51.1% to 48.9% in AtlasIntel/Bloomberg, according to Reuters. The latest surveys point to a near dead heat. Datafolha's October 20–22 poll put Bolsonaro and Lula level at 50% of valid votes each, while Vox Brasil, reported by Exame, had Lula at 50.6% and Bolsonaro at 49.4%. These are poll estimates, not results, and they carry the usual uncertainty about the final margin.

The candidates held their second and final debate on TV Globo on Friday, October 23. The Associated Press reported that they spoke to undecided voters in a tight contest, trading exchanges over crime and workers' rights and accusing each other of wrongdoing. The coverage did not show a clear effect on the race.

Voting is scheduled for Sunday, October 25, with polls open nationwide from 8 a.m. to 5 p.m. Brasília time, the Superior Electoral Court says. The court will cover the vote count starting at 5 p.m. The official count will settle whether the gap between the top two candidates falls in the 4-to-8-point range, or whether the race is narrower or wider.