Compare your estimated probability against offered odds to see whether the wager has positive or negative expected value.
Method
Expected value compares the probability you assign to an outcome with the return offered by the odds. A positive result means the assumptions produce a theoretical long-run gain per modeled stake; it does not predict whether one event will win.
Educational example
At decimal odds of 2.20 and an estimated win probability of 50%, the EV factor is 1.10.
A $10 modeled stake has an expected value of $1 before fees or taxes. The estimate is useful only if the 50% probability is well calibrated.
Compare two available prices using the same probability estimate.
Measure whether historical probability estimates were calibrated before trusting future EV.
Translate a contract price and fee into a break-even probability.
Expected value is highly sensitive to probability error. It also omits limits, account restrictions, changing prices, taxes, liquidity, and the sequence risk created by a finite bankroll.
It means the price is favorable under the probability assumptions entered into the calculator.
Yes. Expected value describes an average across repeated comparable decisions, not one outcome.
Use a documented model, a no-vig market estimate, or another source you can validate out of sample.