Positive EV betting, explained

Expected value (EV) is the average profit or loss you'd make on a bet if you could place it thousands of times. Sportsbooks build a margin into every price, so most bets are -EV: you lose a little on average. A +EV bet is one where the odds are generous enough to overcome that margin.

A team is +150 (decimal 2.50) and you believe its true chance of winning is 43%. On a $100 bet:

1. If it wins (43% of the time) you profit $150.
2. If it loses (57% of the time) you lose $100.
3. EV = 0.43 × $150 − 0.57 × $100 = $64.50 − $57.00 = +$7.50, or +7.5% of your stake.

The odds imply only a 40% chance, so at 43% the bet is +EV. Below 40% it would be -EV.

Your EV is only as good as your probability. The most common approach is to take a sharp market — one that is efficient because it accepts big bets from professionals — and strip out its margin.

Take a moneyline of -120 / +100. The implied probabilities are 54.5% and 50.0%, which add up to 104.5%: the extra 4.5% is the vig. Scaling both back to 100% gives fair probabilities of about 52.2% and 47.8% — fair odds of roughly -109 and +109. Any sportsbook offering better than +109 on the underdog is offering a +EV bet. The no-vig calculator above does this for you.

An edge of a few percent is tiny next to the randomness of individual games. After 100 bets at even money, a bettor with a genuine 3% edge is still behind about a third of the time. That's why disciplined +EV bettors:

• keep stakes small and consistent with a fixed unit size;
• judge themselves on closing line value, not short-term results;
• shop several sportsbooks, because half a point or a few cents of price is often the whole edge;
• keep a complete record in a bankroll tracker.