Room for ChanceThe science of chance

Free interactive tool

Probability and Odds Converter

Convert a probability percentage into one-in-X chance and formal odds against, with clear denominators.

Inputs and results stay in this page. These tools set no cookies, save no browser preferences and send no input data to our server. A CSV downloads only when you request it. Displayed probabilities are rounded; combination counts use exact integer arithmetic.

Understand the result

Probability vs Odds: What Does “1 in a Million” Mean? explains the derivation and common interpretation errors. Compare it with the published Why any repeat arrives sooner than one chosen repeat.

Exact collision curve for 10,000 equally likely outcomes; points show results from 10,000 independent sequences. This is a reduced model of any repeated outcome, not the return time of one chosen lottery line.
Figure 1. Exact collision curve for 10,000 equally likely outcomes; points show results from 10,000 independent sequences. This is a reduced model of any repeated outcome, not the return time of one chosen lottery line.
Download SVGDownload PNGData CSV

Related game generators

Generate a valid line for a game without treating this calculation as a prediction.

Powerball generatorEuroMillions generator

Explore all ten tools · See reproducible experiments