Definition
Expected value (EV) is the average profit or loss per bet if the same bet were placed infinite times. EV = (probability of win × profit) − (probability of loss × stake). Positive EV means the bet earns money long-run. Negative EV means it loses long-run. EV ignores short-run outcomes — a positive-EV bet can lose; a negative-EV bet can win. Every rational betting decision is based solely on whether EV is positive, regardless of recent results.
Worked Example
Bet: Team A moneyline +200 (risk $100 to win $200). Your model: Team A wins 40% of the time. EV = (0.40 × $200) − (0.60 × $100) = $80 − $60 = +$20 per bet. Over 50 identical bets: expected profit = 50 × $20 = $1,000. Same bet if true probability were 30%: EV = (0.30 × $200) − (0.70 × $100) = $60 − $70 = −$10 per bet.
Why It Matters
EV is the only number that matters for long-run profitability. Every other metric (win rate, streaks, record) is downstream of EV — maximize it on every single bet.