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Odds & Probability

American Odds

Also known as: 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.

Related Odds & Probability Terms

Positive Expected Value (+EV)
A bet where the expected return is positive, meaning it will be profitable in the long run if placed repeatedly. A +EV bet occurs when the odds offered are higher than the true probability warrants. For example, getting odds of 3.00 on an outcome with a 40% chance of occurring. Professional bettors exclusively seek +EV opportunities.
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.
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.
True Probability
The actual likelihood of an outcome occurring, independent of the bookmaker's margin. True probability cannot be known with certainty, but it can be estimated through statistical models, historical data, and analysis. When your estimated true probability exceeds the implied probability, you have found a value bet.
Odds Conversion
The process of converting odds between decimal, fractional, and American formats. Decimal to fractional: subtract 1, then simplify (2.50 = 3/2). Decimal to American: if odds >= 2.00, American = (Decimal - 1) x 100; if odds < 2.00, American = -100 / (Decimal - 1). Conversion is essential for comparing odds across different platforms.
Implied Probability (IP)
The probability of an outcome as suggested by the betting odds, expressed as a percentage. Calculated as: IP = (1 / Decimal Odds) x 100. For example, odds of 4.00 imply a 25% probability. Implied probability includes the bookmaker's margin, so the total of all outcomes in a market exceeds 100%.
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