US Senate forecast methodologyBeta

What this is

A 2026 US Senate forecast for the 35 seats on the ballot (33 Class II + the Florida and Ohio specials), combined with the 65 seats not up to give a chamber control probability. Published as a beta. The Senate is materially poll-anchored: every competitive seat is poll-backed, so the documented prior governs mainly the safe and unpolled seats.

How it differs from the global standard

• •Documented per-seat prior: each seat's baseline is a presidential spine — 0.75 × the state's 2024 presidential margin relative to the nation, plus 0.25 × the 2020 equivalent — with explicit, cited adjustments for only two cross-pressured incumbents (Maine and Georgia). No undocumented partisan lean.
• •Safe-seat base: the 65 seats not up in 2026 are counted as 34 Democratic-caucusing and 31 Republican (the two specials, Florida and Ohio, are Republican-held and on the ballot).
• •Control threshold: Democrats need 51 seats for control under a Republican Vice-President (50–50 is Republican control on the tie-break).
• •Poll blending + Monte Carlo: where a seat is polled, polls are blended with the prior; 40,000 simulations per chamber with shared national and region-correlated shocks.

How to read it (beta caveats)

This is a beta forecast: read the control probability with wide uncertainty, the documented priors govern safe and unpolled seats while polls dominate the competitive ones, and the model will be recalibrated as more polling and post-election validation arrive. Current figures are on the live Senate tracker.