TL;DR
- Kalshi, Polymarket and Polymarket US saw combined August volume fall 14.5% to $45.33 billion, ending a year-long streak of monthly growth.
- Kalshi volume declined 7.3% to $37.17 billion, while Polymarket and Polymarket US fell 36.7% to $8.16 billion after the World Cup surge.
- Regulatory pressure around sports contracts is intensifying, while Kalshi continues expanding through a U.S. Open partnership despite the broader slowdown in prediction-market trading activity during August overall.
Kalshi and Polymarket saw combined prediction-market trading volume fall 14.5% in August to $45.33 billion, marking the first month-over-month decline in a year after a World Cup-driven summer surge. Activity had climbed sharply while the tournament ran from June 11 through July 19, leaving August to test whether that pace could persist once the event ended. The key shift is that prediction-market growth finally paused after twelve months of uninterrupted monthly expansion. Even after the pullback, however, August volume remained comfortably above May’s $25.66 billion, showing that activity has not returned to pre-summer levels.
World Cup Momentum Fades As Platform Performance Diverges
Kalshi remained the dominant platform, recording $37.17 billion in August volume, down 7.3% from $40.1 billion in July. Polymarket and Polymarket US experienced a much steeper contraction, with combined volume falling 36.7% to $8.16 billion from $12.89 billion. The divergence suggests the post-World Cup slowdown hit Polymarket’s ecosystem considerably harder than Kalshi’s. The numbers also show that the headline 15% decline masks very different platform-level trends, with Kalshi still accounting for the overwhelming majority of combined activity even as its own monthly trading volume moved lower during a notably active period for event contracts.
The cooling in trading arrives as both major prediction-market operators face increasing regulatory scrutiny in the United States, particularly around sports-related contracts. More than a dozen states have taken enforcement actions or filed lawsuits involving Kalshi and Polymarket, while Connecticut sued Kalshi last week seeking to block sports-event contracts. The market slowdown therefore coincides with a period when legal pressure around sports prediction products is intensifying. That does not establish regulation as the cause of August’s decline, especially after the World Cup boost, but it adds another variable as platforms compete for users and volume.
Kalshi is still expanding its sports presence despite those legal disputes. The company recently reached an agreement with the U.S. Tennis Association to become the exclusive prediction-market partner of the U.S. Open, whose main draw began August 30. It also permanently banned former U.S. Representative George Santos after he violated platform rules by trading a contract tied to whether he would attend the State of the Union. August’s decline now raises the question of whether major sporting events can continue generating durable growth once temporary volume spikes fade. September will offer an early test of that momentum.
