Stake, odds and your estimate of the true chance to the average value of the bet.

Expected value is what a bet is worth on average, if you could make it many times over. It is the chance of winning times the payout, minus the chance of losing times the stake. Positive means the price is in your favor. Negative means it is against you.

The hard part is the true chance. This tool uses your own estimate, so the answer is only as good as that number. The honest way to estimate the true chance is to de-vig the market's two sides, which is what the no-vig calculator does. Guessing high is the most common way bettors talk themselves into a bad price.

A bet can win and still have been negative expected value, and a bet can lose and still have been positive. One result tells you almost nothing. The price, against a fair estimate of the chance, tells you the rest.