A data-driven forecast has raised the odds of Democrats taking control of the Senate, with the party now given a 77.6% chance of winning the majority. The estimate covers all 35 Senate seats in play and suggests a potential shift from the Republicans’ current 53-47 advantage to a 52-48 Democratic majority.
The projection was produced by Thomas Miller, a data scientist and professor at Northwestern University, whose latest calculations are being updated through his Virtual Tout website.
Miller’s forecast gives Democrats the lead in 18 of the 35 contests, compared with 17 for Republicans. The Democratic position is described as particularly strong in North Carolina, Ohio, Texas, Alaska and Maine, while the party is also holding its existing seats in Michigan and Georgia.
Republicans were given an almost 36% chance of retaining control when Miller began applying the methodology on September 19. By 11.30pm on October 23, that figure had fallen to 22.5%.
The probability of a Democratic takeover has also risen sharply since October 14, when it stood at 71.5%. Miller has cautioned that the figures are highly volatile and could change substantially before election day.
How the Senate forecast is calculated
Rather than beginning with opinion polls, Miller uses prices from the prediction markets Kalshi and Polymarket, selected because they have the biggest trading volumes. He then makes statistical adjustments to convert those prices into estimated probabilities and account for the markets’ inherent biases.
The adjusted figures are processed through several time-series analyses designed to identify the underlying factors behind changes in the odds. Miller says those factors explain between 80% and 90% of the movement in the probabilities.
His analysis suggests the Senate contests are closely linked rather than moving independently. Miller believes the words and actions of Donald Trump could be influencing Republican prospects across the country, with the party’s odds rising or falling in multiple states at the same time.
“The states don’t move independently of one another,” he said. “If one moves up for Republicans, chances are they all move up for Republicans and vice versa.”
He added: “The entire market’s driven by what Trump does hour by hour. If voters like what Trump says, the Republican odds rise almost everywhere, when they dislike what he says, the Republican odds drop across the board.”
Miller began publishing his current “NowCasts” on October 22, although the underlying methodology has been running since September 19. The forecast does not guarantee that Democrats will win the majority, but it currently indicates stronger momentum for them than the polls suggest.
