Glossary
Expected value
Expected value, or EV, is the average result you would expect from a bet if you could place it many times. It weighs each outcome by its probability and its payoff. A positive EV bet gains on average over the long run, a negative EV bet loses on average.
Expected value is a long-run average, not a prediction about the next bet. You take each possible outcome, multiply what it pays by how likely it is, and add those pieces together. The result tells you what a bet is worth on average if it could be repeated endlessly.
Say a wager risks 100 to win 100, and you judge the true chance of winning at 55 percent. Over many identical tries you would gain on some and lose on others, and the weighted average would tilt slightly positive. That tilt is the EV.
Why the vig matters here
Because the vig is baked into every price, a bet that looks even money is usually slightly negative EV once the margin is included. Finding genuinely positive EV means estimating the true probability more accurately than the price implies, which is hard and never certain.
Average, not outcome
Positive EV does not mean a bet will win. It means that if the estimate is right, the average over a large number of similar bets leans in your favor. Any single result can still go either way, and estimates can be wrong.
EV is a way to think clearly about price, not a shortcut to profit.