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If polls can be off by about σ points either way (one standard deviation), a candidate leading by m points wins with probability Φ(m / σ), the normal curve. A 3-point lead with polls that can miss by 5 points gives about 73%; the same lead with a 3-point error gives 84%. The calculator also runs backwards: enter a market price and see the lead it implies.
A deliberately simple model: one race, normally distributed polling error, no other information. Real forecasts also weigh fundamentals, correlated errors across states and late news.
Read backwards, the same model turns a market price into the poll lead it matches. With polls that can be off by 5 points:
| Race | Favourite | Polymarket | Matching lead (pts) |
|---|---|---|---|
| Georgia governor | Rick Jackson | 50.5% | +0.1 |
| Nevada governor | Aaron Ford | 55.5% | +0.7 |
| Iowa senate | Ashley Hinson | 57.5% | +0.9 |
| Maine senate | Troy Jackson | 58.5% | +1.1 |
| Ohio senate | Sherrod Brown | 61.5% | +1.5 |
| Texas senate | James Talarico | 64.5% | +1.9 |
| Ohio governor | Amy Acton | 66.5% | +2.1 |
| Kansas senate | Roger Marshall | 67.5% | +2.3 |
Prices from Polymarket via our 2026 midterm forecast, refreshed twice a day. A market price can reflect more than polls: fundamentals, candidate news and money.
Treat the final result as the poll margin plus an error that is normally distributed with standard deviation σ. The leader wins when the error is smaller than the lead, which happens with probability Φ(m / σ). Choosing σ is the whole game: it should cover polling error, turnout surprises and time left before the election, and it is an assumption, not a measured value.
Put real prices into the calculator: every page below shows current odds, 24-hour moves and the market rules.
2026 midterms odds · Senate odds · Governors odds
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Divide the lead by how far off the polls could be (one standard deviation) and read the normal curve: a 3-point lead with a 5-point error is 0.6 standard deviations, about a 73% chance of winning.
It is a judgement call that grows with time before the election and with how unusual the race is; the calculator lets you try several values and see how much the answer moves.
Polymarket prices come from traders, who weigh polls with everything else they know. The table above shows the poll lead each close race's price corresponds to under this model.
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