The close contest between incumbent Luiz Inácio Lula da Silva and Flávio Bolsonaro, following the October 4 first round that produced no outright winner, has left both campaigns focused on maximizing supporter turnout for the October 25 runoff. Historical patterns show second-round participation typically trails the first round amid voter fatigue, while an expanding electorate with a larger share of optional voters over age 70 contributes to gradual abstention increases. Logistical factors such as registration distance and limited enthusiasm in a polarized environment further shape expectations. Trader consensus centers probabilities in the 76-82% range, reflecting these structural trends and the limited time for major shifts before voting.