Prediction markets give Democrats 63% odds to win House and Senate a week out

One week before the Nov. 3 midterm election, online prediction markets see Democrats as two-to-one favorites to win both the House and the Senate, CNBC reported Tuesday ¹. On Kalshi, a trading platform where people bet on events, traders put the chance of a Democratic sweep at 63% ¹.

On a second platform, Polymarket, Democrats have a 65% chance to win both chambers, CNBC said ¹. Kalshi gives Republicans just under a 10% chance of holding both the House and the Senate ¹. It puts the chance of a split Congress at 29%, with Democrats taking the House and Republicans keeping the Senate ¹.

On tapeNBC News · Oct 25

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How the odds have moved

The Kalshi odds have stayed relatively stable since the start of October ¹. Before early September, Democrats had less than a 50% chance of a sweep ¹. Their odds were around 30% earlier in the year, before the start of the U.S.-Iran war and the higher gas prices that have hit consumers, CNBC reported ¹.

The House looks like the safer bet for Democrats. A USA Today Network report updated Oct. 19 said Polymarket gave Democrats a 91% chance of winning the House ². The Senate is tighter. Republicans hold it now, and the same report listed Iowa, Ohio, Maine and Texas as toss-ups in one forecast from Decision Desk HQ, a election-data firm ².

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What the polls say

Polls show Democrats ahead in the national vote for the House and competitive in several Senate races in states that Republicans usually win, CNBC said ¹. The Oct. 19 report listed polling averages with Democrats ahead by roughly 7 to 9 points on the generic ballot, which asks voters which party they plan to back for Congress ². One example was RealClearPolling, which showed Democrats at 50.7% to Republicans at 42.4% ².

House Speaker Mike Johnson, a Louisiana Republican, has cast doubt on those polls ¹. He made the case on Fox News on Monday ¹.

A caution about betting odds

Prediction markets are not polls. CNBC noted that betting platforms do not use the methods that traditional pollsters use, so they are not substitutes for political polls ¹. The odds also have misfired. Markets gave high odds to Flavio Bolsonaro in Brazil's presidential race before polls closed Sunday, yet President Lula da Silva was re-elected ¹.

The platforms say the odds work like any probability. A candidate given a 20% chance should pull off an upset about 20% of the time, according to CNBC ¹. A 63% chance for Democrats also means a 37% chance of some other result ¹.

CNBC disclosed that it has a commercial relationship with Kalshi that includes customer acquisition and a minority investment ¹.

What happens next

Voters decide Tuesday, Nov. 3. The markets will keep moving until then, and they settle using official data from the U.S. Congress ¹.

That matters because Congress writes the laws that set Social Security and Medicare funding. The pattern is that Democrats' odds have climbed as prices rose, but only the votes count. No poll or market can replace turning out to vote.

The Record

1. Sep 16, 2026Before early September, Democrats had less than a 50% chance to sweep both chambers on prediction markets, per CNBC's later account ¹.
2. Oct 19, 2026Polymarket gave Democrats a 91% chance to win the House, per a USA Today Network report ².
3. Oct 26, 2026Brazil re-elected Lula da Silva after markets gave high odds to Flavio Bolsonaro, a reminder of their limits ¹.
4. Oct 27, 2026Kalshi put the chance of a Democratic sweep at 63% and Polymarket at 65% ¹.

Sources

1. CNBC, “One week out, prediction markets see Democrats as favored to sweep Congress” (2026-10-27). cnbc.com/2026/10/27/2026-midterms-prediction-markets-democra
2. NorthJersey.com / USA TODAY Network via Yahoo News, “Latest midterm polls and election odds: Who's winning the House and Senate?” (2026-10-19). yahoo.com/news/politics/articles/latest-midterm-polls-electi

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