Expected Value (EV) in Sports Betting: A Practical Guide
Expected value is the single most important concept in sports betting. Every professional bettor frames decisions around it. Every recreational bettor who loses money consistently is, usually unknowingly, playing negative EV. Here's what it actually means.
What Expected Value Is
EV is the average outcome of a bet placed an infinite number of times. A positive EV bet makes money on average; a negative EV bet loses money on average — regardless of any single outcome.
EV = (probability of winning × amount won) − (probability of losing × amount lost)
Coin flip at fair odds: Bet $100, win $100 at 50% probability. EV = (0.50 × 100) − (0.50 × 100) = $0. Fair bet.
Standard −110 spread bet: Risk $110 to win $100. If the game is a true 50/50: EV = (0.50 × 100) − (0.50 × 110) = −$5. The vig costs you $5 per $110 bet in expectation.
How the Sportsbook Vig Creates Negative EV
The standard −110/−110 line gives the sportsbook a built-in edge:
- Implied probability of both sides at −110: 110/210 = 52.38% each
- Both sides add to 104.76% — the "overround" or "vig"
- To break even at −110, you need to win 52.38% of your bets
Most recreational bettors win 48–50%. The math does the rest.
Finding Positive EV Bets
Positive EV exists when you believe the true probability is higher than the sportsbook's implied probability. Common ways sharps find edges:
- Line shopping: Getting +115 when most books have +105 on the same outcome — the extra 10 cents can flip a break-even bet to positive EV
- Closing line value (CLV): Getting a line before the market sharpens it — a bet at +115 that closes at −105 has clear positive CLV
- Market inefficiencies: Secondary markets (props, alternate lines, smaller leagues) are less sharp than mainstream markets
- Stale lines: Books slow to update to injury news or lineup changes create brief windows of positive EV
Tracking Your EV Over Time
The only way to know if you're a winning bettor is to track expected value on every bet, not just outcomes. A record of 55-45 in a small sample proves nothing. A record of 100 positive EV bets that lost money is consistent with variance, not bad strategy.
Track: bet, line obtained, closing line, implied probability, your estimated probability, EV, outcome. After 200+ bets, your closing line value will tell you whether you have a real edge.
Use our EV calculator to calculate expected value for any bet before you place it.