Plug in the market price, your view of the true probability, and your stake. This Polymarket profit calculator returns expected value (EV), upside if YES wins, downside if YES loses, and EV as a percentage of the bet. Green means the numbers are +EV, red means the price is too expensive for your estimate.
The formula:
EV = ( p × (1 − price) − (1 − p) × price ) × bet
Where p is your true probability (as a decimal). The first term is the win-case profit (you paid price, the share resolves to $1, you net 1 − price), the second is the lose-case loss (the share resolves to $0 and you lose price). EV is just the probability-weighted average.
Positive EV (green) means the market is offering worse odds than your true-probability estimate — these are the trades worth taking. Negative EV (red) means you'd be paying more than the share is worth on your view. The bigger the gap between your probability and the market's, the bigger the edge.
EV doesn't tell you how much to bet — for that, see our Kelly Criterion calculator. And remember: a +EV trade is only as good as your probability estimate. For more on building accurate views, read our Polymarket strategy guide.
A YES share pays $1 if the event resolves YES and $0 if it resolves NO. If the market price is 0.60 and you stake $100, the winning-case profit is $66.67 before fees or slippage because your $100 buys about 166.67 shares and each share nets 40¢. The losing-case downside is the full $100 stake. Expected profit weights those two outcomes by your probability estimate.
Use this as a pre-trade math check, not as a signal by itself. The calculator does not place orders, connect a wallet, or claim the estimate is correct.