Prediction markets achieved a historic milestone during the final week of September 2026, with cumulative weekly trading volume reaching $20.4 billion. According to data from Artemis, this marked the first time weekly volume has crossed the $20 billion threshold, surpassing the previous highs set during the FIFA World Cup in June and July 2026 and the $19.8 billion recorded the prior week.
Kalshi captured roughly 77% of all tracked volume, processing about $15.8 billion of the $20.4 billion total. Polymarket finished a distant second with $3.6 billion in weekly transactions. Nadex followed with $481.9 million, Rothera contributed $272.3 million, and Predict.fun and Opinion each handled around $120 million. The gap between Kalshi and Polymarket is now the widest it has been all year, according to Cryptopolitan.
Weekend activity was especially intense. Daily sector volume reached $4 billion on both Saturday and Sunday, with Kalshi routing approximately $3 billion on each day. Polymarket posted $770.4 million on Saturday and $662.4 million on Sunday.
A significant portion of the volume came from multi-leg combo contracts, or parlays, tied to American football. These contracts pay out only if every selection hits, so they often trade at just a few cents. Kalshi records each contract at its $1 face value payout rather than the price the trader actually paid. As a result, a $20 bet on a long-shot parlay priced at 5 cents buys 400 contracts and appears as $400 in volume. This accounting method means headline volume figures can expand much faster than the money actually at risk.
Three catalysts converged during the record week. The NFL and college football seasons began in September, driving substantial weekend sports flow. The Federal Reserve's September interest rate decision also contributed to steady contract activity. Additionally, short-duration crypto markets tracking Bitcoin and Ether turned over repeatedly as prices moved, while traders began early positioning for the November 3 midterm elections, where control of both chambers of Congress is at stake.
Regulatory challenges remain in the background. On September 25, the 6th U.S. Circuit Court of Appeals ruled that Ohio and Tennessee can regulate Kalshi's sports contracts under their gambling laws, joining the 3rd and 9th Circuits. Polymarket operates both a US exchange and an international Polygon-based venue, while Kalshi holds its CFTC-regulated designation for US users. With the NFL regular season running into early January 2027 and midterm elections approaching, prediction market activity could remain elevated through year-end. September monthly volume has already broken past the previous highs set in July.
