How to use the Probability and Odds Converter
The same chance can be written as a probability or as odds. Enter a win probability p and the tool returns the decimal odds 1/p, the fractional odds (1-p)/p : 1 and the American odds; enter decimal odds d instead and it returns the implied probability 1/d. American odds use -100p/(1-p) when p is 50% or more and 100(1-p)/p when p is below 50%.
One point matters more than the arithmetic. Posted odds already include the seller margin, or overround, so the implied probabilities taken from each price with 1/d add up to more than 100%. Put two or more decimal odds in the list box and the tool reports that sum alongside the margin, the sum of 1/d minus 1. While a margin exists the expected return on a stake stays below the stake itself, and repeated betting makes the expected loss grow.
This page converts figures only. It does not forecast results or win rates, and it quotes no average margin per operator, because such a figure is not confirmed by a public source. Treat the output as a reference. Current as of October 2026.
Frequently asked questions
Because posted odds carry the seller margin, also called the overround. It equals the sum of 1/d minus 1, and the larger it is, the less comes back for the same chance of winning.
A win probability of 50% or more is written as a negative number, below 50% as a positive one. The positive figure is the profit on a 100 stake; the negative figure is the stake needed to win 100.
At a probability of 1 the fractional odds collapse to 0 and the American odds are undefined, so the tool accepts only values above 0% and below 100%.