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Odds & Probability

Expected Value

Also known as: EV

The average amount a bettor can expect to win or lose per bet if the same bet were placed many times. Formula: EV = (Probability of Winning x Profit) - (Probability of Losing x Stake). A positive EV (+EV) indicates a profitable bet over the long term. EV is the single most important concept in professional betting.

Related Odds & Probability Terms

American Odds (Moneyline Odds)
Odds format used primarily in the United States, expressed as positive or negative numbers. Positive odds (+150) show how much profit you win on a $100 bet. Negative odds (-200) show how much you need to bet to win $100 profit. +150 means a $100 bet wins $150 profit; -200 means you must bet $200 to win $100.
Overround (Book %)
The sum of the implied probabilities of all outcomes in a betting market, expressed as a percentage. A fair market totals exactly 100%, but bookmakers add an overround (e.g., 105%) to guarantee a profit margin. Formula: Overround = (1/Odds1 + 1/Odds2 + ... + 1/OddsN) x 100. Lower overrounds indicate better value for bettors.
Negative Expected Value (-EV)
A bet where the expected return is negative, meaning it will lose money in the long run if placed repeatedly. Most bets offered by bookmakers are -EV due to the built-in margin. A -EV bet occurs when the odds offered are lower than the true probability warrants. Recreational bettors predominantly place -EV bets.
No-Vig Odds (No-Juice)
Odds that have been adjusted to remove the bookmaker's margin (vig/juice), representing a fairer assessment of the true probabilities. To calculate no-vig odds, divide each outcome's implied probability by the total overround. No-vig lines are useful for identifying which side of a market has more value.
Probability Distribution
A mathematical function that describes the likelihood of all possible outcomes in a betting event. Common distributions used in sports betting include the Poisson distribution for goals/points, the normal distribution for point spreads, and the binomial distribution for win/loss sequences. Understanding distributions helps bettors build predictive models.
Fair Odds
The odds that would be offered if the bookmaker had zero margin, reflecting the true probability of an outcome. Fair odds are calculated by removing the overround from the market. If the implied probability is 40% with margin, the fair odds are 1/0.40 = 2.50. Comparing market odds to fair odds helps identify value.
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