Polymarket traders gave Democrats a 76% chance of winning the Senate and a 94% chance of winning the House on Election Day, Nov. 3, 2026.
Traders see Democrats taking both chambers
Kalshi's traders landed in nearly the same place, at 75% for the Senate and 94% for the House. A Democratic House paired with a Republican Senate sat a distant second on Polymarket at 19%.
The House call is the easier one. All 435 House seats are on the ballot, along with 35 of the 100 Senate seats.
The Senate math is tighter. Republicans hold it 53-47, so Democrats need a net gain of four seats, and the models disagree more there, with some races possibly unsettled on election night.
Money has poured into the question. Polymarket's Balance of Power market drew more than $58M in volume, and a related Kalshi contract topped $100M.
Kalshi's chief executive said more than $1.4B traded on bets tied to the races.
History says the result fades from stocks after about three months
The S&P 500 was higher a year after all 20 midterms since 1946, with an average gain of about 14%, and the weakest showing was a 0.1% rise after the 1946 vote.
A longer look back tells the same story. Across 38 midterms since 1874, the index rose in the 12 months after 32 of them, or 84% of the time.
That same 14% average gain beats the roughly 11% average for any 12-month stretch.
Most of that return shows up after the first month, which averaged a 0.5% gain, with the following three months averaging 6% and six months averaging 10%.
Stock Gains After Midterms Build Over the Following Year
Average S&P 500 gain after Election Day across 38 midterms since 1874, %
Line chart. Average gain, %. 1 month: Average Gain (%) 0.50%. 3 months: Average Gain (%) 6%. 6 months: Average Gain (%) 10%. 12 months: Average Gain (%) 14%.
Source: The Motley Fool
Outcome matters most in the short window. After the seven midterms that left Democrats running Congress, stocks rose an average of 11% over the following three months and were higher every time.
The one Republican hold, in 2002, saw stocks drop 8% as the country moved toward war in Iraq.
The samples are too small to trade on
In five of those seven Democratic-control years, Democrats already ran Congress. Only twice did a Republican president lose both chambers, in 1954 under Eisenhower and 2006 under George W. Bush, and the following year brought gains of about 33% and 7%.
The path between those endpoints can be rough. When Trump lost the House in 2018, the S&P 500 fell nearly 15% by Christmas Eve as the Fed kept hiking and the US-China trade fight escalated, then finished about 12% higher a year after the vote.
For the roughly 150M Americans who own stock, the record argues for sitting still through the noise.
Election bets themselves have shrunk as a share of the action, with politics accounting for only about 1% of October volume on Polymarket and Kalshi, against more than 60% during the 2024 election.
