Polymarket US gains ground as weekly prediction trading reaches $19.46 billion

Weekly trading across Kalshi, Polymarket US and Polymarket International rose 3.9% to $19.46 billion in the Sept. 21-27 period, keeping activity close to the $20 billion mark. Kalshi remained by far the largest venue, but Polymarket US supplied roughly two-thirds of the aggregate weekly increase as its share of tracked volume rose sharply.

DeFi Rate’s three-platform tally put the previous week’s total at $18.72 billion. Kalshi accounted for $15.66 billion, or 80.5% of the total, after a 2.6% increase that set a weekly record for the exchange. Kalshi and Polymarket US together represented just over 95% of the tracked trading.

Polymarket US volume climbed 21% to $2.83 billion, adding about $492 million during the week, compared with Kalshi’s roughly $395 million gain. Its portion of the combined total increased from 12.5% to 14.6%, while Polymarket International fell 13.5% to $964.1 million and its share slipped to 5%.

Combination contracts accounted for virtually all of Polymarket US’s growth. Their weekly volume rose 44.4% to $1.53 billion, from $1.06 billion, and represented 54.1% of platform trading, up from 45.4% a week earlier. About $471 million of the platform’s $492 million weekly expansion came from those contracts, or 95.9% of the increase.

The shift was especially pronounced on Sunday, Sept. 27, when Polymarket US processed nearly $760 million, up from about $592 million on the previous Sunday. Combination-contract volume rose to nearly $469 million, and made up 61.7% of the day’s activity, compared with 50.4% a week earlier.

Football still dominated the largest individual Polymarket US markets. All 10 of the week’s biggest markets were football contracts, led by Colts-Chiefs at about $27.7 million, Giants-Rams at $23.2 million and Falcons-Packers at $16 million. Yet those 10 markets collectively represented only 4.4% of total platform volume.

By identifiable sports category, NFL contracts generated $267 million on Polymarket US, narrowly ahead of tennis at $263.1 million. College football accounted for $225.6 million and Major League Baseball for $201.8 million.

Bitcoin contracts also rose sharply, from roughly $453,000 in the previous week to $50.7 million. Fifteen-minute contracts produced about $45.7 million of that total, or 90%, though Bitcoin still made up only 1.8% of Polymarket US trading for the week.

Kalshi’s activity was concentrated late in the week. It handled about $8.6 billion from Friday through Sunday, equal to 54.9% of its weekly volume, with Saturday reaching $2.9 billion before Sunday set a daily record of $3.24 billion. Its trade count rose from 85.3 million to 88.1 million.

The figures extend a broader expansion in prediction-market activity. CNBC reported earlier this month that daily notional volume across the sector had become consistently measured in billions during the 2026 fall season, following a surge that began with the NFL season in September 2025. Robinhood’s JB Mackenzie described the period as a prediction-market “supercycle.”