Expected value is the long-run average outcome of a bet if you placed it infinite times. Positive EV means the bet makes money over time; negative EV means it loses. Enter your stake, the offered odds, and your honest win probability. Last updated: May 2026.
Expected value weighs what you win against what you lose, each scaled by how often it happens. The formula is EV = (p × profit) − (q × stake), where p is your win probability, q is 1 − p, profit is your winnings if the bet hits, and stake is what you risk. The calculator first converts your American odds to decimal (positive: (odds ÷ 100) + 1; negative: (100 ÷ |odds|) + 1), then derives profit as stake × (decimal − 1).
From there it reports EV in dollars, EV as a percentage of stake (EV ÷ stake × 100), and the break-even probability, which is 1 ÷ decimal odds — the win rate at which EV is exactly zero. If your entered probability beats break-even, EV is positive and the verdict reads +EV; if it's lower, EV is negative. That comparison, your honest probability versus the price's implied probability, is the entire game.
Default inputs: a $100 stake at +150 with a 45% win estimate. Convert the odds: (150 ÷ 100) + 1 = 2.50 decimal, so profit if you win = $100 × 1.50 = $150. With p = 0.45 and q = 0.55, EV = (0.45 × $150) − (0.55 × $100) = $67.50 − $55.00 = +$12.50.
That's an EV of +12.50% of stake — a strong positive-value spot. The break-even probability is 1 ÷ 2.50 = 40.00%, so your 45% estimate clears the bar by five points, which is what drives the edge. But sensitivity cuts both ways: drop your estimate to 40% and EV falls to exactly $0; to 38% and it turns negative at −$5.00. The calculator flags +EV here, yet note you'd still lose this individual bet 55% of the time — the value only shows up over a large sample.
In my own work, the hard part is never the arithmetic — it's earning an honest probability. I'd rather understate my edge and pass on a marginal +EV bet than talk myself into a number I can't defend. Never wager money you can't afford to lose chasing a thin edge.
Expected value (EV) is the average outcome per bet if you could replay the exact wager forever. A +$5 EV bet earns about $5 per attempt on average, even though each individual bet wins or loses fully.
EV = (win probability × profit if won) − (loss probability × stake). If your stake is $100 at +150 odds and you estimate a 45% win chance: EV = (0.45 × $150) − (0.55 × $100) = $67.50 − $55 = +$12.50.
The win rate you'd need to exactly break even at the given odds. It equals 1 ÷ decimal odds. If your true probability is higher than break-even, the bet is +EV. If lower, it's -EV.
It's worth betting in the long run if your probability estimate is accurate. In the short run, variance dominates — even a 60% +EV bet loses 40% of the time. Size your stakes using the Kelly Criterion to survive variance.
Compare your model's probability (or a sharp book's no-vig probability) against the offered odds. If your estimate is meaningfully higher than the implied probability, you've found a +EV bet.