Expected Value (EV)

Expected value, usually shortened to EV, is a statistical measure that shows the average result of a bet if you placed it over and over under the same conditions. You work it out by multiplying each possible outcome by its probability, then adding those products together. A positive expected value (+EV) tells you a bet pays off over the long run, while a negative expected value (-EV) means you can expect to lose money on it over time. Both professional and dedicated recreational bettors treat expected value as the single most important number for deciding whether a wager is worth making.

To really get EV, you have to separate the result of any one bet from the mathematical edge behind it. A +EV bet can still lose on any given night, and a -EV bet can still win. What counts is the pattern that shows up across hundreds or thousands of wagers. Bettors who keep finding and placing +EV bets will, given a big enough sample, come out ahead. Those who keep taking -EV bets will watch their bankroll shrink, no matter how many short winning streaks they hit along the way.

Example

Say you figure a team has a 55% chance of winning a game, and the bookmaker offers odds of +110 (decimal 2.10) on that team. The EV calculation for a $100 bet looks like this: (0.55 x $110) - (0.45 x $100) = $60.50 - $45.00 = +$15.50. That means, on average, you’d expect to profit $15.50 for every $100 you wager on this kind of bet over the long run. Even though you’ll lose 45% of the time, the payout when you win more than makes up for those losses.

Key Points

• Foundation of profitable betting: Every winning long-term strategy is built on spotting and taking advantage of positive expected value opportunities.
• Requires accurate probability estimates: An EV calculation is only as good as your estimate of the true probability of each outcome.
• Short-term results may differ: A single bet, or even a run of bets, can land well off the expected value thanks to variance.
• The bookmaker’s edge is built-in: Most bets offered by sportsbooks carry a negative expected value for you, because the odds include a margin (vig) tilted toward the house.
• Comparison tool: EV lets you weigh up different wagers on the same scale, whatever the sport, bet type, or odds format.