Combined monthly trading volume for Kalshi and Polymarket fell to $45.33 billion in August, down 14.5% from July and marking the first monthly decline since August 2025, according to The Block data. Trading activity had surged during the June 11 to July 19 World Cup period before easing after the event ended. Kalshi posted $37.17 billion in August volume, down 7.3% month over month, while Polymarket and its U.S. platform recorded a combined $8.16 billion, down 36.7%. Even with the pullback, August volume remained well above May's $25.66 billion.