Kalshi prices a 64% chance of Democratic control and Polymarket 66%. Kalshi's contract traded about $35.5 million in a single day, roughly seven times Polymarket's total volume on its version.
With six weeks to go before the midterm elections, the two largest prediction markets agree on the direction of the Senate race and nearly on the size of the lead.
Kalshi's contract on which party will control the Senate after the 2026 elections priced a 64% chance for Democrats and 36% for Republicans on Thursday morning, with the Democratic side up a point on the day. Polymarket's equivalent contract priced Democrats at 66% and Republicans at 35%, unchanged from Wednesday.
The prices reflect where traders are putting money. They are not polls and not forecasts of the result.
The two platforms differ sharply in scale. Kalshi's contract traded $35.5 million in a single day. Polymarket's has drawn about $5.1 million in trading since it opened. On those figures, one day of Kalshi volume is about seven times Polymarket's lifetime total on the same question.
The Democratic lead in these markets comes from behind. Republicans hold the Senate 53 to 47 and are defending 22 of the 35 seats up this year. Democrats would need to gain at least four seats for an outright majority. Kalshi's market commentary describes Democratic candidates as leading or competitive in several Republican-held seats, including Alaska, Iowa, Maine, Ohio and Texas.
The agreement between the platforms carries information of its own. Kalshi and Polymarket draw different users, operate under different regulatory arrangements and differ widely in volume. Prices that land within 2 points of each other suggest the Democratic edge is not an artifact of one platform's trader base.
Both contracts will reprice as individual races firm up before the vote. The five states Kalshi highlights are likely to drive much of that movement, since Democrats' path to a four-seat gain runs through Republican-held seats. The gap between the two platforms is also worth tracking: if it widens, one market is reading the same news differently.