Prediction markets had a sports summer.
According to The Block, combined monthly trading volume across Kalshi, Polymarket, and Polymarket US fell 14.5% in August to $45.33 billion, marking the first month-over-month decline in a year.
That decline came after a World Cup-driven surge. The tournament ran from June 11 to July 19, and prediction-market volume rose sharply through the summer. The combined monthly total was $25.66 billion in May, climbed through June, and reached roughly $53.0 billion in July.
The August pullback matters, but so does the level. At $45.33 billion, August volume was still about 77% above May.
For investors, the chart is less about one monthly decline and more about product-market fit. Sports gives prediction markets a repeatable calendar of events, high-frequency outcomes, and mass-market attention. That can make trading volume less dependent on election cycles or one-off news shocks.
The caveat is regulatory risk. Kalshi and Polymarket continue to face scrutiny from state regulators, especially around sports contracts. But the data shows why the fight matters: sports may be the wedge that makes prediction markets mainstream.