With just 38 days until the November 3 midterms, political prediction markets are pricing a rare split verdict: Republicans a modest favorite to hold the Senate, Democrats a slight favorite to flip the House. Kalshi and Polymarket, the two largest US-accessible venues for election trading, together showed more than $84 million in weekend volume across congressional contracts — the heaviest 72-hour window of the cycle. Below is the snapshot traders are actually pricing right now, contract by contract, along with what the crowd appears to be missing.
Senate Control: GOP 61%, Democrats 39%
Kalshi’s flagship “Which party will control the Senate after 2026 elections?” contract has drifted steadily upward for Republicans since Labor Day, closing Friday at 61 cents to the “Republican” side. Polymarket’s equivalent market prices the GOP at 60%, well inside a normal cross-venue spread. The move is not driven by any single race so much as by three toss-ups tilting the same way in the last two weeks.
The three seats doing most of the work in the Senate topline:
- Ohio (Moreno vs. Sherrod Brown rematch attempt is not on the ballot — open seat): GOP nominee priced at 67% to hold. Brown declined to run again, and the Democratic nominee has trailed in every non-partisan poll released since August 20.
- Montana: Republican incumbent at 71%. This contract has been the steadiest of the cycle, rarely moving outside a 68–73% band since June.
- Michigan (open seat): The lone bright spot for Democrats among the marquee races. Democratic nominee priced at 58%, up from 51% three weeks ago after a strong second debate.
Two contracts to watch for late movement: Pennsylvania (Democratic incumbent 54%, but the market has traded a full 12-point range in the last 10 days) and Arizona (Democratic incumbent 52%, essentially a coin flip that will likely decide whether the GOP majority is a comfortable 52 or a fragile 51).
House Control: Democrats 56%, GOP 44%
The House side is the mirror image. Kalshi’s “Which party will control the House?” contract closed at 56 cents Democratic on Friday, its highest print since May. Polymarket sits a touch lower at 54%. The bid has come almost entirely from redistricting-driven pickups in New York, California, and North Carolina, plus one late-breaking retirement in a Trump +2 Virginia seat.
The generic ballot contracts also tell the story. Kalshi’s “Democratic margin on the House popular vote” market prices a most-likely outcome of D+2.4, with the tails skewed toward larger Democratic margins than smaller. That is consistent with an expected Democratic seat gain of 8 to 14 — enough to flip a chamber where Republicans currently hold a five-seat working majority.
The most volatile individual-race contracts of the last week:
- NY-17: Democratic challenger jumped from 44% to 57% after the incumbent’s fundraising report showed a $2.1M cash-on-hand deficit.
- CA-27: Republican incumbent slipped to 41% after the LA Times endorsement went the other way.
- PA-08: Toss-up moved to a genuine 50/50 for the first time all cycle; volume tripled Friday.
The Split-Government Contract Is the Biggest Bet on the Board
Perhaps the most interesting single market is Kalshi’s derivative contract, “Will the same party control both chambers after 2026?” It is priced at just 34% Yes — meaning the market is putting a two-in-three probability on a divided Congress starting January 2027. That is the highest split-government probability at any point in the last four cycles at this stage.
Volume on that contract has topped $9.4M in the last week alone, larger than most individual Senate race markets combined. It is where sophisticated traders appear to be expressing the view that the topline contracts on each chamber are correlated more loosely than casual observers assume.
Where the Crowd Might Be Wrong
Two contracts stand out as potentially mispriced, based on our read of the underlying fundamentals against the current market prices.
First, the Senate GOP net gain ladder. The market’s implied distribution centers on a net gain of 1 seat, but assigns only 18% probability to a net gain of 3 or more. Given how tightly Ohio, Montana, and Nevada are correlated with the national environment, that tail feels thin. A 4-point generic-ballot swing between now and Election Day is well inside normal cycle-to-cycle volatility, and would put all three seats and one of Pennsylvania or Michigan in play.
Second, the House GOP hold contract at 44%. That number would be defensible if the redistricting-driven pickups were all in the bag, but three of the newly-drawn Democratic-leaning seats still have Republican incumbents polling within 3 points. The market is treating those as done deals; they are not.
What to Watch This Week
Three catalysts will move these prices between now and next weekend:
- Tuesday’s Q3 fundraising reports, which historically move at least one Senate contract by 5+ points.
- Wednesday night’s Ohio Senate debate — the only debate remaining in a market currently trading 67/33.
- The DOJ’s expected announcement Friday on the ongoing federal probe of a sitting GOP House member. Kalshi opened a specific contract on this Friday morning; it is currently priced at 38% for an indictment before the election.
The through-line of every one of these catalysts is that they can only widen the price of the split-government contract, not narrow it. Which is why that contract, more than any individual race, is the one worth watching in the final month.
Where to Trade These Markets
All contracts referenced above are actively traded on both major US-accessible venues.
- Kalshi — CFTC-regulated, offering the deepest liquidity in individual race contracts and the only venue running the split-government derivative and the DOJ-indictment contract.
- Polymarket — The largest crypto-native venue, with the tightest spreads on chamber-control topline contracts and the biggest position limits for size traders.
For a full breakdown of how these two venues stack up on fees, liquidity, and available contracts, see our 2026 rankings of the top prediction markets.
Prices in this article reflect settlement prints as of Friday, September 25, 2026, from Kalshi and Polymarket. Markets can and do move quickly; check both venues for live prices before trading.