Brazil traders bet on a wider Bolsonaro margin

The under-4% contract sits at 20% as the 4-8% band takes a 50% lead.

In one line: Flávio Bolsonaro wins Brazil's 25 Oct runoff by at least 4 points of valid votes; the 20% still left on a closer finish is too high.

Traders cut the chance that Flávio Bolsonaro wins Brazil's runoff by less than 4 points to 20% on 12 Oct, from 46% on 5 Oct. The contract pays if he wins and the gap between the top two candidates' shares of valid votes is under 4 points. It touched a 7-day high of 68% on 5 Oct and has lost 48 points since then. It fell 26 points over the 7 days and 6.5 points in the last 24 hours, and today it sits 1 point above its 7-day low of 19%.

The money went to the next band up. A Bolsonaro win by 4 to 8 points now leads the event at 50%, with 8 to 12 points at 15% and 12 or more at 3%. A Lula win by 4 to 8 points trades at 0%. The four Bolsonaro bands sum to 88%, in line with what both venues give him to win outright: 87% on Polymarket and 88% on Kalshi. Two separate books agree on the winner. This event is pricing only the size of the win.

The shift is large for one week, and it hangs together. Traders did not lift Lula; they moved weight from a narrow Bolsonaro win to a wider one. A candidate both venues make so strong a favourite should lead by more than a near tie, so the 4-to-8 band is the natural centre of the event. The weak point is speed, because a 48-point fall from the 5 Oct high in seven days can run ahead of the evidence.

The call: Bolsonaro wins the 25 Oct runoff by 4 points or more of valid votes, and the 20% still left on a closer finish is too high. The best case against it is that runoffs tighten late, and if the final fortnight narrows the race, this week's fall will look like an overreaction. The official count on 25 Oct settles it, and a Bolsonaro margin under 4 points proves the call wrong, as would this contract climbing back above 46% before polling day. For readers who never trade it, the call says Brazil's runoff produces a clear winner rather than a near tie.