Kalshi and Polymarket Face Their Biggest Midterm Test as Election Bets Top $1.4 Billion

Prediction markets are having their biggest midterm election ever. On Election Day, Tuesday, Nov. 3, Kalshi said its midterm-related trading volume had passed $1.4 billion, according to data supplied to Fortune. The Washington Post, in its own analysis, found Americans had wagered nearly $1.9 billion on the midterms as of late Monday, across more than 7,000 different outcomes.

Important: market odds are not election results. Most polls were still open as of Tuesday evening, and no outcome should be read from trading prices. For actual results, check your state’s official election website.

What are Kalshi’s midterm odds?

As of Tuesday afternoon, traders on Kalshi were leaning toward Democrats. Fortune reported that Kalshi gave Democrats a 93% chance of winning control of the House and a 73% chance of taking the Senate.

Reuters reported that on Monday, prediction market prices aggregated by analytics firm BetInt implied a 95% chance of Democrats taking the House and a 76% chance for the Senate. Odds move constantly as money comes in, so these numbers are snapshots, not forecasts locked in place.

Some of the most-traded markets on Kalshi, per Fortune:

In Texas, Fortune said traders gave Democrat James Talarico a 71% chance against Republican Ken Paxton in the Senate race, and gave Republican Gov. Greg Abbott a 65% chance against Democrat Gina Hinojosa. Those are trader prices, not polls or results.

Kalshi vs. Polymarket

Kalshi and Polymarket are the two biggest platforms. Both let users buy “yes” or “no” contracts on outcomes. Reuters reported that Kalshi listed $1.33 billion in trading volume across all midterm bets on Monday, while about $145 million had been wagered on Polymarket’s congressional markets, according to the Anti-Corruption Data Collective (ACDC).

ACDC said more than 28,000 midterm markets had been opened. A handful of contests, including Senate races in Texas, Michigan, Maine and South Carolina, account for most of the trading volume.

Why this election is a test for prediction markets

The platforms rose to prominence in 2024, when traders favored Donald Trump while polls largely showed a toss-up. But Reuters and Fortune both pointed to recent misses:

• Brazil. Kalshi and Polymarket prices implied only about a 20% chance that President Luiz Inácio Lula da Silva would beat Flávio Bolsonaro in last month’s runoff, which Lula won, Reuters reported.
• Wisconsin. In the August Democratic primary for governor, traders gave Francesca Hong about a 95% chance, but David Crowley edged her out by less than half a percentage point, Fortune reported.

“Tuesday does, in fact, represent a real test for the new wave of prediction markets,” Vanderbilt Law School associate dean Yesha Yadav told Reuters.

There are also misconduct concerns. Reuters reported that several candidates bet on their own races, and ACDC research found political markets can be moved with relatively small bets. Kalshi and Polymarket say they have stepped up controls. Kalshi blocks politicians and campaign workers from political wagers, according to Reuters.

Are election predictions accurate?

Academic research, including a 2025 Vanderbilt study of nearly 2,500 markets on the 2024 election, has generally found prediction markets well calibrated at scale, Reuters reported. That means contracts priced at a given probability tend to come true about that often. But Vanderbilt professor Joshua Clinton cautioned that “how accurate the price is for any specific market is impossible to know.”

FAQ