Expected Value (EV) Calculator

Is your bet +EV?

Every profitable trader is really doing one thing: betting when their estimate of the true probability beats the market's price. Expected value puts a number on it. Enter what you think the chance is, and the price the market is offering, and this calculator tells you whether the bet makes money in the long run — and by how much.

The formula

EV = (p × win profit) − ((1 − p) × stake), where p is your estimated win probability. Your edge is simply your probability minus the market's implied probability (its price). Positive edge, positive EV.

Worked example

You think an outcome is 60% to happen. Polymarket prices it at 50¢ (50% implied). On a $100 stake your EV is +$20 — a 20% expected ROI and a +10-point edge. That's a clear +EV bet.

From EV to bet size

Once a bet is +EV, the next question is how much to stake. Feed the same numbers into the Kelly criterion calculator for the optimal size, and use the no-vig calculator to sanity-check the market's fair price. Sharper probability estimates come from the analytics tools in the directory.