What each number means
Implied probability translates decimal odds into a percentage: it is the chance associated with that price. Fair odds work in the opposite direction, converting an estimated probability into odds without a bookmaker’s margin. The concepts are related, but they are not interchangeable. The implied probability of an offered price may include the bookmaker’s margin; fair odds based on your own estimate depend on how sound that estimate is.
Understanding fair odds and implied probability helps you compare the price on offer with the chance you assign to an outcome. This is a mathematical comparison, not a guarantee that the outcome will happen or that a bet will be profitable.
Convert odds into implied probability
To calculate raw implied probability, divide 1 by the decimal odds and multiply by 100. For odds of 2.00, the calculation is 1 ÷ 2.00 = 0.50, or 50%. At 1.50, it is 1 ÷ 1.50 ≈ 0.6667, or 66.7%. Odds of 4.00 correspond to 25%.
The calculation gives the percentage associated with a price; it does not establish that this is the event’s true chance. In a market with several possible outcomes, the raw implied probabilities can add up to more than 100%. This excess is called the overround and reflects the margin built into the prices. So each raw percentage should not be treated as a margin-free probability.
Calculate and use fair odds
To convert an estimated probability into fair odds, write the percentage as a decimal and divide 1 by it. If your estimate for an outcome is 40%, use 0.40: 1 ÷ 0.40 = 2.50. With an estimate of 55%, the calculation is 1 ÷ 0.55 ≈ 1.82. These figures are prices corresponding to estimates, not certain predictions.
Then compare the offered odds with your fair odds. If your estimate is 40% and the available price is 2.00, your fair odds are 2.50, so the offered price is lower. Under that estimate, the available price does not reach the fair price. The conclusion depends on the estimate: if it is wrong, the comparison may be wrong too.
In a market with multiple outcomes, removing the margin requires considering the probabilities for all of them, not just the odds for one selection. A total above 100% reveals the raw margin, but does not automatically turn an estimate into the truth. Use the calculations to understand prices and assumptions, remembering that short odds indicate a higher implied probability, never certainty.