Kalshi Hits $15.66B as Combination Bets Lift Weekly Trading

Kalshi, Polymarket US and Polymarket International combined for approximately $19.46 billion in trading volume from Sept. 21-27, up 3.9% from $18.72 billion the week before, according to a DeFi Rate analysis of the three venues. Polymarket US supplied most of the incremental growth, pushing its share of the combined total from 12.5% to 14.6%.

Kalshi still ran away with the week in absolute terms. Its volume rose 2.6% to a record $15.66 billion, good for 80.5% of the three-platform total, and Sunday alone produced a fresh daily high of $3.24 billion just a week after Kalshi’s first $3 billion day.

Combination bets did nearly all the work

Polymarket US volume jumped 21% to $2.83 billion, adding $491.6 million in new trading compared with Kalshi’s $395.4 million gain, per the DeFi Rate figures. That’s a notable swing given Kalshi’s much larger base, and it built on Kalshi’s continued lead in prediction-market volume even as smaller rivals close the gap.

Nearly all of that growth traced to one product. Combination contracts on Polymarket US rose 44.4%, from $1.06 billion to $1.53 billion, and their share of the platform’s volume climbed from 45.4% to 54.1%. DeFi Rate’s breakdown shows combinations accounted for 95.9% of Polymarket US’s week-over-week increase, meaning everything else on the platform grew by roughly $20 million.

Football topped the leaderboard, but not the ledger

All 10 of Polymarket US’s largest individual markets were football, led by Colts-Chiefs at $27.67 million and Giants-Rams at $23.23 million. Even so, those 10 markets accounted for just 4.4% of total platform volume, underscoring how much trading has moved into the combination format that prediction markets’ NFL-driven download and engagement gains have helped normalize this season.

NFL volume reached $267.0 million and tennis was close behind at $263.1 million, with college football at $225.6 million and MLB at $201.8 million. Bitcoin markets, meanwhile, went from roughly $453,000 the prior week to $50.7 million, almost entirely through 15-minute and hourly contracts.

A split market, still tilted toward Kalshi

Polymarket International moved the opposite direction, falling 13.5% from about $1.11 billion to $964.1 million and slipping to a 5.0% share. Kalshi and Polymarket US together now account for just over 95% of volume across the three venues DeFi Rate tracks, with Polymarket US responsible for roughly two-thirds of the week’s net increase.

That divergence between Polymarket’s two products comes as Polymarket’s US prediction market expansion continues to draw a larger slice of trading away from its offshore sibling. Whether combinations hold above half of Polymarket US volume next week, rather than whether the market clears $20 billion, is the number DeFi Rate says is worth watching.

The post Kalshi Hits $15.66B as Combination Bets Lift Weekly Trading appeared first on ReadWrite.