Payout is not probability
A binary options payout is the published return for a successful contract, not its probability of winning. A 90% payout does not mean the contract has a 90% chance of success.
Multiply each possible net payoff by its evidenced probability, include ties and refunds, and sum the branches to reproduce the stated expected value per unit staked.
Under full loss and no fees, EV per unit = p * net payout - (1 - p); at an 80% net payout and p=50%, EV is -0.10 unit.
Model wins, losses, refunds, ties, voids, rejected orders, fees, and early exits separately. Expected value requires a defensible probability for each state; payout alone cannot provide that probability.
Break-even math matters, and so does where the payout was observed. Broker homepages, platform screenshots, help pages, and comparison sites may describe different payout contexts, so the guide separates ordinary payout from selected-contract ceilings.
Ordinary payout shown for common contracts.
Highest published payout, often limited to selected contracts or strike settings.
The win rate needed to break even before costs, friction, and rule mistakes.



