Polymarket expected value calculator
Expected value per YES share = your probability − price − fee. If it is positive, the market price is lower than your estimate of the true chance.
Why EV matters
A single trade either wins or loses, but over many trades your results converge on the expected value. Traders who only take positive-EV positions, size them sensibly and keep fees low tend to come out ahead; everyone else pays the spread.
The calculator assumes the NO price is 1 − YES price; in practice the spread makes the other side slightly more expensive. The weak point is the probability you type in. Be honest, compare with other sources and use our Kelly calculator to size positions conservatively.
Ready to try it? Check it is available where you live, then open Polymarket.
Open PolymarketFrequently asked questions
What is a good edge on Polymarket?
Anything clearly positive after fees and spread, but small edges are easily wiped out by estimation errors. Many traders look for several percentage points.