Kalshi, Polymarket Starting to Price the Midterms as Blowout

With just over five weeks left before the 2026 midterms, prediction markets have become as much a part of election coverage as polling averages.

Kalshi and Polymarket are increasingly converging on a strong Democratic midterm performance.

Initially, Kalshi and Polymarket agreed on a strong advantage for Democrats in the House but were split on the Senate with Kalshi giving a slight edge 52% to Republicans, but Polymarket, in sharp contrast, gave a 66% edge to Democrats for the Senate.

The difference has now been wiped away and Kalshi and Polymarket are pricing Democrats as a 92% favorite to retake the House and roughly 60% to retake the Senate.

Why does this matter? Six weeks out from the 2024 election, Polymarket priced Harris vs. Trump as essentially a coin flip but things started to move quickly for Trump in the following weeks. By a week before Election Day, Trump was trading around 66% on Polymarket.

The point being that it’s worth taking a closer look at prediction markets over the next few weeks if you’re looking for hints on the upcoming midterms.

Here’s a closer look at what Polymarket and Kalshi are saying about the midterms.

The House: About as Close to Consensus as Markets Get

On Kalshi, the market pricing House control puts Democrats at 91% and Republicans at 9%, with more than $38 million traded on the contract as of late September. The number has ticked even further towards Democrats over the past few days, giving them a commanding lead.

Polymarket’s combination markets have a similar lead. Adding its "Democrats Sweep" and "Republican Senate, Democratic House" outcomes puts the implied probability of Democratic House control well above 90%.

Both platforms are pricing a wave election for the House, driven by the same structural facts: Republicans hold a narrow majority, midterms are historically brutal for the president's party, and Democrats currently enjoy one of their strongest generic ballot leads of the cycle.

The Senate Is No Longer a Coin Flip

Earlier this month, the Senate looked relatively safe for Republicans, but now that is under threat as well.

Around Sept. 12, both Kalshi and Polymarket shifted dramatically towards Democratic control in the Senate. Earlier, the two leading prediction markets diverged significantly, but at the time this article was published, both had stabilized around 62% for Democrats retaking the Senate.

Why the shift? There’s a variety of factors, but recent polling has shown voters getting disgruntled about health care, the cost of living and the war in Iran.

Texas and Iowa have surprisingly become legitimate battlegrounds where Democrats have a chance of flipping the status quo.

A week ago, several of these races were close to coin flips, but there has since been a sharp swing toward Democratic candidates.

Some of the most dramatic include James Talerico in Texas and Sherrod Brown in Ohio where both candidates moved 10 points ahead of their opposition.

Maine and Michigan were already leaning Democrat but moved even further in that direction. Iowa is the one race where Republicans still hold the edge.

Beyond Control: Seat Counts and Wave Scenarios

Kalshi also runs markets on the overall scale of the outcome. Its “blue wave” market is now priced at about 84% Yes, while the more aggressive “blue tsunami” scenario sits near 49%, putting a much larger Democratic gain close to a coin flip. Kalshi defines a blue wave as Democrats finishing with at least 218 House seats and 49 Senate seats, while a blue tsunami requires at least 235 House seats and 51 Senate seats.

The odds that Democrats finish with more than 52 Senate seats sit around 36%, while a 50-50 chamber is priced near 16%, both plausible outcomes rather than fringe bets.

What the Trading Volume Says

Trading volume matters because it's a rough proxy for how much real conviction, and how much scrutiny, sits behind a given price. The House control market alone has drawn more than $38 million on Kalshi, while Polymarket's Senate market and its combined Balance of Power markets have moved at least $18 million. Election officials have taken notice too. PBS News reported that trading volume on Kalshi and Polymarket has been "skyrocketing" this cycle, with officials cautioning that billions of dollars could ultimately be wagered on questions like House and Senate control before November. That's a separate debate from whether the prices are accurate, but it's part of why these markets get more media attention with every cycle.

Markets vs. Polls: Mostly Aligned, Senate Still Lags

On the generic congressional ballot, Nate Silver's Silver Bulletin polling average had Democrats up roughly 7.5 points in mid-September, climbing from a 6.4-point lead at the start of the month, and closer to an 8-point edge once adjusted for likely voters. That lead is large enough, historically, to match the kind of decisive House flip both Kalshi and Polymarket are pricing. On the House, in other words, the markets and the polls are telling the same story. 

It’s roughly the same story for the Senate, although independent race analysis remains more cautious about Senate control.

The Bottom Line

Just over five weeks out, prediction markets are getting more confident about a strong Democratic performance in the midterms.

The House looks heavily tilted toward Democrats in both markets, while the Senate remains considerably more competitive, with several toss-up states, and a national mood that hasn't fully sorted out how it applies to a map this specific. For readers trying to understand how these odds actually get priced, that's the value of watching more than one market at once. Agreement tells you what's settled, while discrepancies tell you where to keep watching.

Figures pulled September 28, 2026.