What is +EV in sports betting?

+EV (positive expected value) means a bet pays more than its real chance of winning is worth. A 55% bet at even money is +EV: it loses 45% of the time and still makes money over many bets.

The dollar version

Bet $10 at even money (+100) on something that wins 55% of the time. Over 100 bets you win 55 of them for $550 and lose 45 of them for $450. You lost 45 bets and finished up $100. The gap between what the bet pays and what it is worth is the edge. Here it is 10 cents on every dollar.

Why the win rate alone fools you

Every price has a break-even win rate. Win more often than that and you make money; win less often and you lose, even while hitting more than half your bets.

So a 60% record can lose and a 45% record can win. The price decides, not the pick.

How to find a +EV bet

1. Work out the real chance. A model does this best. Without one, the average price across several books is a fair starting point.
2. Turn the price into a chance. -110 implies 52.4%, +150 implies 40%. (How odds turn into percentages.)
3. Compare. When your chance is higher than the chance the price implies, the bet is +EV. The bigger the gap, the bigger the edge.
4. Shop. The same bet is often priced differently at four books. The best price can turn no edge into a 3% edge.
5. Size it small. A 3% edge is real and it is small. One unit is 1% of your bankroll.

What +EV feels like

Losing often. A 55% bet loses almost every other time, and losing streaks of five or six happen to everyone. The edge shows up over hundreds of bets, which is why the size of each bet matters more than any one result.

How Mammoth Picks uses it

Our model works out each result's chance and compares it with the price at FanDuel, DraftKings, BetMGM and Caesars. When the price pays more than the chance is worth by enough, that is a pick. It posts with its bet size at least 30 minutes before the game and is graded in public after, win or lose.

Questions

Does a +EV bet always win?

No. It wins more often than its price assumes, over many bets. Any single +EV bet can lose, and losing streaks happen even when the math is right.

What win rate do I need at -110?

52.4%. Below that you lose money at -110 even while winning more than half of your bets. The standard price carries the book's cut.

Can a parlay be +EV?

Yes, if every leg is +EV at its price. The edge is small and the swings are large, so a parlay should be sized smaller than a single bet.

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