Expected Value (EV)
Calculate expected value from an estimated probability, odds, and stake.
18+ where legal. Educational calculator only. Bet sizing outputs are not financial advice.
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How to Calculate Expected Value in Sports Betting
Expected Value (EV) is the single most important concept in professional sports betting. It answers the question: "If I place this bet 1,000 times, do I make or lose money?" A positive EV bet is one you expect to profit from over time. A negative EV bet loses money over time, regardless of whether it wins today.
The formula: EV = (p × b) − (1 − p), where p is your estimated win probability and b is the net decimal profit (odds − 1). If you estimate 55% probability on odds of 2.00 (evens), EV = (0.55 × 1) − 0.45 = +0.10. You expect to profit $0.10 per $1 bet — a 10% ROI — long term.
The challenge: bookmakers already embed a negative expected value into their odds via the vig. At standard -110 American odds (1.909 decimal), you need to win 52.4% of bets just to break even. Most recreational bettors win far less than 52.4% against the spread, creating a permanent -EV position. Professional bettors find situations where their estimated probability is meaningfully higher than the implied probability.
The break-even probability (shown as "Break-Even %" in our calculator) is the win rate you need to profit at the given odds. If the offered odds imply 52.4% but your model gives the team 57%, you have a genuine +EV edge of approximately 4.4%. This is how professional betting syndicates operate — finding systematic mispricing, not picking winners.
The EV Formula
EV per unit = (p × (Odds − 1)) − (1 − p) ROI % = EV × 100 Break-Even = 100 / Odds (% win rate needed to profit) EV > 0 → Profitable long-term (+EV bet) EV < 0 → Losing long-term (−EV bet) EV = 0 → Break-even (fair odds)
EV Examples
Odds 2.10, your probability estimate 55%. EV = (0.55 × 1.10) − 0.45 = +0.155 (+15.5% ROI). Strong value bet. Break-even was 47.6%; you estimate 55%.
Odds 1.91, your probability estimate 50%. EV = (0.50 × 0.91) − 0.50 = −0.045 (−4.5% ROI). Standard vig situation — you're paying the house 4.5%.
Frequently Asked Questions
What is Expected Value in sports betting?
Expected Value is the average profit or loss per unit bet across a large number of identical wagers. Formula: EV = (p × (odds−1)) − (1−p). Positive EV means you profit long-term; negative EV means you lose. Most recreational bettors bet at −5% to −10% EV without realizing it.
What EV% is considered good for betting?
Professional bettors target 3–8% EV per bet. Even +2% sustained over hundreds of bets produces significant profit. Any consistently positive EV is worth pursuing at appropriate stake sizes via Kelly Criterion.
How is EV different from ROI?
EV is forward-looking and per-unit. ROI is backward-looking and aggregate. Use EV to evaluate future bets; use ROI to assess past performance. Our calculator shows both: EV per unit and ROI% (EV × 100).
Can I consistently find positive EV bets?
Yes, but it requires a probability model better than the market. Approaches: statistical models (Elo, xG-based), line shopping across 5+ bookmakers, early market betting before lines sharpen, and exploiting public bias on high-profile games.