Brazil's stock market lost 18% after betting on a coin flip
On Monday 26 October 2026, Brazil's biggest stocks fell 13.88% in one day. By Friday the loss was 18.12%.
Traders had put about 80% on one winner. The polls said 51 to 49.
First, what is a stock index?
Take a country's biggest companies. Add up how they are doing. That one number is the index.
Brazil's is the Ibovespa. It hit a record 209,067 on 9 October 2026.
Now watch what happened to that number.
It lost 18% in five trading days
-13.88%
Ibovespa, one day, Monday 26 October
It closed at 205,082.56 on Friday 23 October. On Monday it closed at 176,608.23. By 30 October it was 167,921.80, down 18.12% on the week.
Five bad sessions took the index 19.68% below its record
Source: B3 closes via Rio Times, Trademap, Suno, Genial. 3 Nov is derived. B3
And that is the gentle way to count it.
Abroad, it was worse
-20.42%
Ibovespa in dollars, 26 October
Foreigners count in dollars. The real fell 8.21% against the dollar that day: R$4.99 on Friday, R$5.40 on Monday.
R$734bn of market value vanished. That is about US$136bn.
So who had been so sure?
Bettors said 85%. The polls said a coin flip.
On a betting site, the runner-up's chance of winning jumped from 63% to 84.8% in one day. His round-one lead was only 1.87 points.
The poll average stayed at 51.0 to 49.0, inside the margin of error.
The bet was far bigger than the polls
Source: Polymarket via press; Rio Times and Poder360 poll averages; TSE. Odds are a chance of winning. Polls and results are vote shares. TSE
Foreign money bought into the bet
On 5 October foreigners bought R$10.06bn of shares in one day, the most since early 2021. In five sessions they bought R$13.15bn.
The index hit its record four days later.
Foreign buying built up, then flipped
Source: B3 flows via press. Hatched bars are derived from press totals, not B3 primary data. June and July not found. B3
Did anyone see the exit coming?
The exit started before the vote
Foreigners sold for seven sessions in a row from 22 October, R$11.99bn in all. The index hardly moved at first.
- 5 OctOdds jump to 84.8%. The index gains 7.70%, its best day since March 2020.
- 9 OctRecord close, 209,066.90.
- 21 OctA poll shows a one-point race.
- 22 and 23 OctForeigners sell about R$1.04bn, then R$2.94bn.
- 25 OctThe count ends. The runner-up loses.
Source: B3 flows via press; Rio Times; Poder360. 22 Oct figure implied from the seven-day total.
Sunday: the favourite lost
51.78 to 48.22
Runoff, 25 October, % of votes
Lula won by about 4.4 million votes. It was the first time a first-round winner lost a runoff. The polls had missed the margin by about 5.6 points.
The market had one night to take it in.
Monday: trading stopped
At about 10:00, B3 hit pause for the first time since March 2020. A circuit breaker halts trading when the index falls 10%.
The index closed down 13.88%, the fifth worst day since 1994. It missed fourth place by 0.04 points.
Only four days since 1994 were worse
Source: B3 daily series via Genial; B3 notice B3 aciona circuit breaker. Reports disagree on the new futures limits set that morning, so none are shown.
The average hid a 68-point gap
Magalu fell 58.23%. Suzano rose 10.08%. Only 6 stocks rose that day.
Losers often owe money. Vamos carried R$11bn of net debt.
Five stocks lost about half; a few gained
Source: Trademap, Suno, Folha, Bloomberg Línea; Vamos Q2 2026 results.
The winners got paid in dollars
+8.89%
Embraer, 26 October
Embraer, Suzano and Vale sell abroad. The dollar bought more reais that day, so their sales were worth more at home.
A weak real also changes what things cost.
A weak real keeps interest rates high
Imports cost more when the real falls. Analysts say a 10% weaker real adds up to 1 point to yearly inflation.
On 4 November the central bank held its rate at 13.75%, with every member agreeing. Five expected cuts were put off.
.jpg){kind=link}
Source: BCB Copom statement 4 Nov and minutes no. 282, 10 Nov; analyst estimates in the press.
It had happened before, only smaller
Peru in April: exit polls pointed one way, the count another. Colombia in June: the market piled into the favourite, who won by about 1 point.
Four of the five cases we checked fit. Peru's June runoff went the other way, and the market rose.
Same shape, smaller drops
Source: Reuters via The Star; ThePrint; Ámbito; Bloomberg Línea; Trading Economics. Different indexes, one-day moves.
The warning sign, in plain words
- Bettors say 75% or more for one side.
- Polls say the race is within 2 points.
- Foreigners bought R$10bn or more in five days.
- Then they start selling while the index sits still.
Brazil showed step 4 on 22 and 23 October. The drop came 4 days later. The odds gap had been open for 21 days.
It can fool you. Polls may shift late, and world news moves flows.
The market put 80% on a race the polls called even.
The warning was the gap between the bet and the polls. Foreigners were the first to leave.
Two weeks on, the Ibovespa was 19.40% under its record, and the finance minister was still unnamed.
Sources and method
- Prices, flows, odds and polls come from press reports of B3, the central bank and Polymarket. B3 and BCB pages could not be fetched directly, so treat these as press figures.
- Dollar loss: index divided by the 26 Oct spot rate (5.4029) and an implied 23 Oct rate (4.993). With the central bank's daily average rate it is -21.13%.
- Contested: the week figure (-18.12% by B3 arithmetic, -17.3% on one site), futures limits, credit default swap levels. 6 Nov close: 168,498.45, which is 19.40% under the record.
- B3: Aviso ao Mercado, circuit breaker notice. Central bank: Copom 282 minutes, 10 Nov. Elections: TSE.
- Press: Rio Times, Trademap, Suno, Genial, Folha, Bloomberg Línea, Ámbito, Poder360, Reuters via The Star, ThePrint, Trading Economics.
- Status: no court or regulator has found wrongdoing in the market move. The runner-up's claims about the vote are allegations the electoral court and prosecutor rejected. This is not investment advice.
- Photos: Fulviusbsas, ProtoplasmaKid, Oleg Yunakov, Felix Gottwald, Mariordo, Banco Central do Brasil and a TSE-site contributor, via Wikimedia Commons (links in each caption).