EV Calculator — Expected Value & Betting Edge

Enter three inputs: your stake (the amount you plan to bet), your win probability as a percentage (your honest estimate of the chance you win this bet), and the decimal odds offered by the bookmaker. Click "Calculate Expected Value" to see the result instantly.

The primary result is the Expected Value in dollars — shown in green if positive (+EV) and red if negative (−EV). You also see the EV as a percentage of your stake, the break-even probability (the minimum win rate needed to profit at these odds), and the potential profit and loss outcomes.

A single bet result means little on its own — expected value is a long-run concept. A +EV result means that if you placed this exact bet hundreds of times, you would expect to profit on average. A −EV result means the house edge is working against you and you will lose money over time at these odds and probability.

Expected value is calculated as the probability-weighted average of all possible outcomes:

1. Define inputs:
   • p = win probability (decimal, e.g. 0.55)
   • q = loss probability = 1 − p
   • Profit = Stake × (Decimal Odds − 1)
2. Expected Value: EV = (p × Profit) − (q × Stake)
3. EV %: EV% = (EV ÷ Stake) × 100
4. Break-even probability: p_break = 1 ÷ Decimal Odds × 100

The break-even probability is the win rate at which EV equals exactly zero. For 2.0 decimal odds (even money), you must win 50% of the time to break even. For 2.5 odds, you need 40%. Any time your estimated win probability exceeds the break-even threshold, you have a positive expected value bet.

Note that expected value assumes your probability estimate is accurate. The quality of your EV calculation is entirely dependent on the quality of your probability estimate. Overconfident bettors consistently overestimate their win probability and therefore overestimate their EV.

Example 1 — Positive EV Sports Bet

You believe a team has a 55% chance to win a game. The bookmaker prices them at 2.0 decimal odds (even money), implying only a 50% win probability. You bet $100.

• Profit if win: $100 × (2.0 − 1) = $100
• Loss if lose: −$100
• EV = (0.55 × $100) − (0.45 × $100) = $55 − $45 = +$10
• EV% = $10 / $100 = +10%
• Break-even probability: 50%

Your 55% estimate is 5 percentage points above the break-even threshold of 50%. Every $100 you bet at these odds and this probability yields an expected profit of $10. Over 100 such bets, you would expect to profit approximately $1,000 — though individual results will vary significantly due to variance.

Example 2 — Negative EV Parlay Leg

A bookmaker offers +250 decimal odds (3.5) on a longshot. You estimate the team has a 25% chance of winning. Stake: $50.

• Break-even probability: 1 ÷ 3.5 = 28.6%
• Profit if win: $50 × (3.5 − 1) = $125
• EV = (0.25 × $125) − (0.75 × $50) = $31.25 − $37.50 = −$6.25
• EV% = −$6.25 / $50 = −12.5%

Despite the attractive +250 odds, the bet is −EV because your estimated 25% probability falls below the 28.6% break-even threshold. The bookmaker has correctly priced the vig into this line. Placing this bet repeatedly would result in losing 12.5 cents for every dollar wagered on average.

How to Find +EV Bets in Practice

The key skill is developing win probability estimates that are more accurate than the bookmaker's implied probabilities. Professional bettors do this through statistical modeling, tracking line movement, and exploiting situations where sharp money has moved a line but a different book has not updated yet. Line shopping across multiple books is the simplest way to find +EV: if your "true" probability is 52% and one book is offering 2.05 odds (implying 48.8%), that is a mathematically positive EV bet — even without a complex model.