Find out if a bet has positive expected value. Enter the bookmaker odds and your estimated true probability to see if the bet is profitable long-term. Includes Kelly Criterion for optimal stake sizing.
Kelly Criterion
Enter odds and probability to calculate expected value.
Expected Value (EV) measures the average profit or loss per bet over the long run. A positive EV means the bet is profitable over time.
Formula: EV = (Probability × Profit) - ((1 - Probability) × Stake). If you believe a team has a 55% chance to win at odds of 2.00, EV = (0.55 × 1) - (0.45 × 1) = +0.10 per unit.
Kelly Criterion suggests the optimal stake size based on your edge. Full Kelly can be aggressive, so most bettors use Quarter Kelly (25%) for a safer approach.
Kelly Formula: f = (bp - q) / b, where b = decimal odds - 1, p = win probability, q = 1 - p.
Expected Value (EV) is the single most important concept in profitable betting. It answers a simple question: if I placed this bet thousands of times, would I make money or lose money on average?
A bet with positive EV (+EV) is one where the odds offered by the bookmaker are higher than they should be based on the true probability. Over time, consistently betting on +EV opportunities is the only reliable way to profit from sports betting.
A bet with negative EV (-EV) means the bookmaker has priced the odds below fair value. Most casual bets are -EV — that is how bookmakers make money. Understanding this distinction separates informed bettors from recreational ones.
The hardest part of using this calculator is estimating the true probability of an outcome. There is no perfect method, but here are approaches professional bettors use:
The Kelly Criterion is a mathematical formula that tells you the optimal percentage of your bankroll to stake on a bet, based on your edge. It maximises long-term growth while managing risk.
However, Full Kelly staking is aggressive and leads to large bankroll swings. Most professional bettors use Quarter Kelly (25%) or even less. This reduces volatility dramatically while still capturing most of the long-term growth.
If the Kelly Criterion suggests "No bet", it means the odds do not offer enough value to justify a wager at any stake. Listen to the math and skip the bet.
A bookmaker offers 2.40 on Team A to win. You analyse their recent form, home/away record, and goal statistics, and estimate their true win probability at 48%.
Enter 2.40 as odds and 48 as probability. The calculator shows EV = +0.152 per unit — a strongly positive bet. The breakeven probability is 41.7%, so as long as you believe Team A wins more than 41.7% of the time, the bet has value. The Kelly Criterion will suggest an appropriate stake based on your bankroll.