Implied Probability Calculator
Every price is a probability in disguise. Converting it back is the first step in working out whether a bet is worth taking — if you think the real chance is better than the price implies, that's an edge.
Calculator
How to use the implied probability calculator
Enter a price in whichever format you have it and the calculator returns the chance it implies, along with the same price in the other two formats and what a stake would return.
The implied probability includes the bookmaker's margin, so it always overstates the true chance. Add up every outcome in a market and you'll get more than 100% — the excess is the vig. To see what the book actually thinks, strip that out with the no-vig fair odds calculator.
The formula
Each format converts to probability differently:
Decimal: probability = 1 ÷ odds
American (positive): 100 ÷ (odds + 100)
American (negative): odds ÷ (odds + 100)
Fractional a/b: b ÷ (a + b)
A worked example
A side is $2.50 to win. Its implied probability is 1 ÷ 2.50 = 40%, and a $50 stake would return $125 for a $75 profit.
The same price is +150 in American odds and 3/2 as a fraction. If your own read is that the side wins closer to 45% of the time, the bet has value — you're being paid as though it happens 40% of the time.
