2026 midterm odds: split Congress now 26.5 percent on Polymarket

Polymarket's midterm markets spent the weekend repricing the shape of Congress, and the move has pushed the split-outcome arm to its most expensive level of the week. As of 08:00 UTC Monday, October 26, the event contract for a Democratic sweep of both chambers sits at 64.5 percent, down from 66.5 percent in our October 22 piece, while the outright split of a Republican Senate and a Democratic House has climbed to 26.5 percent, per the platform's Gamma API.

The numbers that matter sit in the balance-of-power distribution, not the headline margin. Four days ago the Democratic sweep arm was the story at 66.5 percent. Today it trades near 64.5 cents, a drift of roughly two points that has not come from the Republican sweep, which stays pinned near 7.5 percent. Instead the probability has leaked into the one outcome pollsters and risk desks have flagged all cycle: divided government, with Democrats holding the lower chamber and Republicans taking the Senate.

Related reading: 2026 midterm election odds: Polymarket prices a Democratic Congress sweep at 66.5 percent.

For the broader framework, see our prediction markets coverage.

That split arm, listed on Polymarket as Republican Senate with Democratic House, is the event's highest conviction addition of the last several days at 26.5 percent. The inverse split, a Democratic Senate with a Republican House, is effectively off the board at under one percent. The market is not pricing both chambers as coin flips; it is pricing a specific, asymmetric division of power.

The structure is worth a close read because the volume is not where the probability is. The House control event is the day's heaviest traded politics market on the platform, moving about 2.13 million dollars in 24 hours, more than any single Fed or election contract at this timestamp. Within it, the question of whether Democrats control the House holds 91.5 percent on roughly 981,000 dollars of 24 hour volume, while the Republican arm, at 8.5 percent, has drawn even more trading at about 1.15 million dollars. The Senate market is thinner, around 209,000 dollars of 24 hour volume, with Democrats at 64.5 percent and Republicans at 35.5 percent.

Related reading: Fed December 2026 hike odds: Polymarket prices 74.5% for a 25 bps move after jobless claims print at 194,000.

That pattern, heavy flow into the long-shot arm while the favorite holds its price, is the classic signature of active hedging or positioning rather than a genuine shift in expected outcome. A market that suddenly believed the Republican sweep was coming would reprice the sweep contracts themselves; instead the money is concentrating in the arms nobody expects to win, which is what markets look like when participants are buying downside protection into an event with under a week to go.

The calibration check comes from the individual chamber contracts. Polymarket prices Democrats to keep the House at 91.5 percent and to retake or hold the Senate at 64.5 percent. Multiplying those two levels gives roughly a 59 percent joint probability, which is below the 64.5 percent the explicit sweep contract carries, a gap that is normal because the two chamber races are correlated through national conditions and because the categorical event imposes mutually exclusive outcomes that sum to a partition. The residual goes to the split-Republican-Senate arm and a small other bucket.

Related reading: Prediction markets show Democratic advantage in 2026 House race while Senate remains a tossup.

All four cited markets share the same resolution schedule: each is scheduled to close November 4 at 04:59 UTC, after the polls close on November 3, and settlement follows the certified outcome per the venue's rules. That makes the entire public beta of the race a discrete, dated contract with a hard resolution date, which is what separates these event markets from a perpetual poll average.

Resolutions

No covered market from prior weeks settled in this window. The ledger shows no due rows as of this run, so this piece files four live markets rather than closing any of last week's.

Related reading: Fed rate hike odds: 86.5% hold vs 54% hike; who's right.

What to watch

The split-Congress arm at 26.5 percent is the number to track into election day. If Democrats hold the House at a steady 91 to 92 percent while the Senate leg wobbles, expect the divide to keep widening in the balance-of-power event, and volume to keep concentrating in the Republican-Senate arms. The other dated resolution on the calendar is the Federal Reserve's October 28 decision, where Polymarket prices a hold near 94.5 percent and Kalshi's hike line hovers near 93.5 percent, both firm into Wednesday's announcement. Prediction markets are pricing outcomes as probabilities and movements as information; neither line is a recommendation.

Data as of 08:00 UTC, October 26, 2026. Sources: Polymarket Gamma API market and event endpoints (outcomePrices, volume24hr, endDate) accessed October 26, 2026; prior-week comparative read from our October 22 midterm odds piece. This content is for informational purposes only and does not constitute financial advice. Past performance is not indicative of future results. Consult a qualified financial advisor before making investment decisions.