Open data
The numbers behind this site, free to download. The files refresh each time the forecast does (several times a day); this copy is from Oct 18, 9:14 PM ET. Each race also has its own file at /data/race/<race id>.json with polls, candidates, fundraising and odds over time.
| File | What’s in it |
|---|---|
| races.csv | One row per race: odds for each side, rating, projected margin, polling average, who holds the seat now and whether it is likely to flip. |
| chambers.csv | Chance each party controls the Senate and House, for all three model versions. |
| forecast.json | Everything on the home page: national mood, chamber odds and seat distributions, markets, sources. |
| races.json | Every race in one file, with all three model versions. |
| history.json | Odds over time for both chambers and every race (before Sept. 28, 2026 a backcast; see the methodology). |
| generic.json | Generic-ballot average, trend and the polls in it. |
| approval.json | Presidential approval average, trend and the polls in it. |
| pollsters.json | Pollster ratings used to weight polls. |
Reading the columns
- chance_*_out_of_100: the share of the model’s 40,000 simulations that side won. It is the same “X in 100” shown on the site, not a poll result and not a certainty.
- dem_side / rep_side: the Democratic-side and Republican-side finalists. When an independent or a second candidate of the same party is the main alternative, that candidate sits on the non-Republican (or non-Democratic) side and the party column says so.
- projected_margin_dem_minus_rep: points; positive means the Democratic side leads. polling_avg_margin_… is the adjusted poll average before blending with the other inputs.
- flip:
likely(50 in 100 or better that the seat changes parties),could(25–49), orno. In the ten states with new House maps, the “current holder” is the sitting member’s party on the old lines. - forecast_version: polls, fundamentals, experts. The default shown on the site is
fundamentals. 506 races are in the file.
Using it
Please credit Bellwether and link to this site when you use these numbers, and say which date they are from. The forecast figures are ours; the polls inside the polling files belong to their pollsters and come through VoteHub and the pollsters’ own releases, and the candidate lists come from Wikipedia (CC BY-SA 4.0). See the methodology for every source. Want to show a live card on your own site? Use the embed buttons on any race, or the chamber cards on the Senate and House pages. A feed of the biggest changes is at /feed.xml.