Plug in the market price, your view of the true probability, and your stake. The calculator returns expected value (EV) in dollars and as a percentage of the bet. Green means take it, red means skip.
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.