Odds to Probability Converter

How it is calculated

The tool reads fractional odds a/b ("a to b") as two separate numbers, where a is the profit and b the stake. The implied probability is p = b ÷ (a + b) × 100, and the matching decimal odds are (a + b) ÷ b, both shown to two decimals. Decimal and American odds must be rewritten as a fraction first: decimal odds D become a = D − 1, b = 1; American +N becomes a = N, b = 100; American −N becomes a = 100, b = N (so −110 is 100 and 110, giving 52.38%). Both numbers must be zero or more and b must be above zero, otherwise there is no result; a = 0 gives 100%. The probability is the bookmaker's implied figure: it includes their margin, so the implied probabilities of all outcomes in a market add up to more than 100%.

Common mistakes

• Typing a decimal price such as 3.50 into the first box and leaving the second at 1. That means "3.5 to 1" (decimal 4.50, a probability of 22.22%), a different price from decimal 3.50, which is a = 2.5, b = 1.
• Swapping a and b. 2/5 and 5/2 are opposite prices: one is a favourite (71.43%), the other an outsider (28.57%).
• Entering a negative American price such as −110 in either box. The tool shows no result for negative values; convert it first (−110 becomes a = 100, b = 110).
• Treating the implied probability as the true chance. It includes the bookmaker's margin, so it overstates the real probability.
• Leaving b at 0. A zero stake gives no valid price, so no result appears.