Expected value (EV) is the average outcome of a bet if you placed it thousands of times. A positive EV bet (+EV) wins money over time. A negative EV bet (-EV) loses money over time — regardless of short-term results.
The formula: EV = (Win probability × Profit) − (Loss probability × Stake)
A coin flip bet at -110 odds on heads: you win $90.91 on a $100 bet (at -110), with a 50% true probability.
Same coin flip but the book offers +100 odds (even money):
Now suppose you have a model that says team A wins 60% of the time, but the book offers +120 (implied: 45.5%):
BetIQ's model outputs a win probability for every team. Edge % = (Model probability − Market implied probability) × 100. Picks with positive edge are surfaced to you. The higher the edge, the stronger the bet — and the more units Kelly sizing recommends.
Even strong +EV bets lose frequently. A 70% favorite loses 30% of the time. You need a large enough sample (100+ bets) for your edge to show up consistently. This is why bankroll management matters — you must survive variance to realize your edge.