Implied Probability

Traditional odds format used primarily in the UK and Ireland, expressed as a fraction (e.g., 5/2). The first number represents potential profit and the second represents the stake required. So 5/2 means you win $5 for every $2 staked. Fractional odds of 1/1 (evens) are equivalent to decimal odds of 2.00.

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.

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.

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.

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.

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.