Prediction markets closed September 2026 at record volume, powered by the start of the NFL season. For the week ended September 27, trading across Kalshi, Polymarket US and Polymarket International reached approximately $19.46 billion, up 3.9% from the prior week, according to volume tracker DefiRate.
Kalshi drove most of the total. The CFTC-regulated exchange logged a record $15.66 billion in weekly volume for the week ended September 27, a 2.6% gain, per DefiRate, and set a new single-day high of $3.24 billion that Sunday. Friday through Sunday alone generated about $8.60 billion, more than the first four days of the week combined, DefiRate reported.
The opening NFL weekend had already set the pace. Prediction markets had their best two days ever on the first Saturday and Sunday of the NFL season, generating at least $5.83 billion, according to Aldrin Research, as cited by Barron's. Ninety-one percent of that volume was tied to sports and combo trading, and $4.89 billion of it took place on Kalshi, per Barron's. Analysts at Jefferies estimated Polymarket US saw $404 million in Sunday trading, Barron's reported, though the platform's data was not yet available at the time.
Polymarket US grew fastest among the venues. Its weekly volume jumped 21% to $2.83 billion for the week ended September 27, lifting its share of the three-venue total to 14.6% from 12.5%, DefiRate reported. Nearly all of that growth came from combination contracts, which surged 44.4% to $1.53 billion and now account for more than half of all Polymarket US volume, per DefiRate. Meanwhile Polymarket International moved the other way, falling 13.5% to $964.1 million in the September 21-27 week, per DefiRate.
Football dominates the leaderboards even as the volume mix broadens. In NFL Week 1, tracked NFL prediction-market volume topped $1 billion across the major venues, DefiRate reported. For the week ended September 27, all 10 of Polymarket US's largest individual markets were football, led by Colts-Chiefs at $27.67 million, though those 10 markets together accounted for just 4.4% of the platform's volume, per DefiRate. On Polymarket US, the NFL was the largest identifiable sports category at $267 million, with tennis right behind at $263.1 million, DefiRate reported.
Trade counts tell the same story at quarterly scale. Prediction markets logged about 1.1 billion trades in the third quarter of 2026 through September 25, a record, TokenPost reported. That was more than twice the roughly 490 million trades of the first quarter and above the second quarter's 709 million, with Kalshi generating most of the increase, per TokenPost.
The influx of mainstream money is reshaping venue economics. DraftKings more than doubled its weekly prediction-market volume for two weeks in a row heading into the NFL season, Barron's reported, and ran advertising that denigrated the user experience on Kalshi. FanDuel and other sports betting operators are market making on Kalshi, Barron's reported, and FanDuel's parent company Flutter said in its second-quarter earnings report that it expects to generate $50 million in market-making revenue in the second half of this year.