The average outcome of a bet over a large number of repetitions — positive EV means the bet profits long-term; negative EV means it loses.
Expected Value (EV) is the mathematical average outcome of a bet if it were placed thousands of times. The formula: EV = (probability of winning × profit) − (probability of losing × stake). A positive EV bet will generate profit over a large enough sample, even if individual bets lose.
Example: you believe a team has a 55% win probability. The bookmaker offers 2.10 decimal odds (net profit of 1.10 per unit staked). EV = (0.55 × 1.10) − (0.45 × 1.00) = 0.605 − 0.45 = +0.155, or +15.5% edge per unit staked.
Professional bettors do not try to predict every match correctly — they consistently find and back positive EV opportunities. Over hundreds of bets, the mathematics of positive EV guarantees long-term profit, even with a win rate below 50% (if the odds are high enough).
Negative EV bets lose money over time regardless of short-term luck. The bookmaker's overround ensures that backing random selections at market odds is always a negative EV exercise.
Value Betting
Betting at odds that are higher than the true probability of the outcome — finding bets where the bookmaker has underestimated the chances of an event.
Implied Probability
The probability of an outcome embedded in bookmaker odds — calculated by dividing 1 by the decimal odds.
Kelly Criterion
A mathematical formula that calculates the optimal fraction of your bankroll to stake on a bet, maximising long-term growth given your estimated edge.
Overround (Vig / Juice)
The bookmaker's built-in profit margin — the amount by which the implied probabilities of all outcomes in a market sum to more than 100%.
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