Brazil’s presidential vote: why finishing first may not be enough

A candidate can finish comfortably ahead in Brazil’s presidential election and still have to face voters again. For anyone following President Luiz Inácio Lula da Silva and Senator Flávio Bolsonaro, that distinction determines whether the first round chooses a president or sends the two leading candidates into another contest.

Lula and Bolsonaro closed their campaigns on October 3, ahead of the October 4 election scheduled in Reuters’ report, republished by MarketScreener. Lula marched through São Paulo; Bolsonaro joined a motorcycle caravan in São Paulo state and later rallied in Rio de Janeiro. Both expressed confidence in victory. Those statements were campaign predictions, not election results.

The rule described by Reuters requires a first-round winner to receive more than half of valid votes. Blank and null ballots are excluded from that calculation. If nobody reaches the required majority, the two candidates with the most votes advance to a runoff—a second election between them.

Beating every rival separately is different from beating all rivals combined. A candidate might have a substantial advantage over the nearest opponent while the remaining candidates collectively have just as many votes, or more. The gap between first and second place therefore cannot, by itself, establish an outright victory.

Imagine 100 presidential ballots, including 10 blank or null votes, leaving 90 valid votes. A candidate with 46 votes receives 46 ÷ 90 × 100 ≈ 51.1% and clears the threshold; 45 votes are exactly 50% and are insufficient. Divide those same 90 valid votes 45–30–15, and the leader is 15 votes ahead of the nearest rival but has no majority. The candidates with 45 and 30 would advance. These are hypothetical numbers illustrating the rule, not Brazilian election results.

The easily missed detail is what the percentage is a percentage of. In that example, 46 votes represent only 46% of all ballots cast, yet they constitute a majority of valid votes. Excluding blank and null ballots changes the total against which each candidate’s support is measured. It does not give those ballots to a candidate or redistribute them among the contenders.

Registered voters, people who turn out and valid presidential votes are also different quantities. Registration describes the electorate; turnout describes participation. A candidate’s share of valid votes describes how votes credited to candidates were divided. The victory test uses that last total. Winning a majority of valid votes does not, by itself, establish support from a majority of everyone registered to vote.

A runoff gives the two finalists another election to contest. Their first-round totals determine who advances, but cannot establish how voters will choose between them afterward. A first-round lead therefore does not guarantee a second-round win. Reuters identified October 25 as the date for that conditional second round.