Odds Calculator & Probability Converter
Turn any odds into a clear percentage chance — and back again. Enter decimal, fractional or American (moneyline) odds, or a probability, and see all four formats update together. A clear, no-nonsense converter that runs entirely in your browser.
How to use the Odds Calculator
Enter a probability, or odds in decimal, fractional or American form.
All other formats update instantly from your input.
The summary shows the implied probability percentage.
Use it to line up odds quoted in different styles side by side.
About this tool
Different parts of the world quote odds in different ways. Decimal odds (popular in Europe and Australia) show the total return per unit staked. Fractional odds (traditional in the UK) show profit over stake, like 5/2. American or moneyline odds use a positive number for the profit on a 100 stake and a negative number for the stake needed to win 100.
All of them encode the same thing: an implied probability. Decimal odds d imply a probability of 1 / d. This converter applies the standard formulas used across the industry so you can translate between formats and read the underlying percentage at a glance. For the maths behind these conversions, see explanations from sources such as Wikipedia’s article on odds and Investopedia.
This odds calculator is an educational maths tool for converting between odds formats. It is not betting or financial advice and does not predict results. Please gamble responsibly and only where legal in your jurisdiction.
Frequently asked questions
How do I convert decimal odds to probability?
Implied probability equals 1 divided by the decimal odds. So decimal odds of 2.0 imply 1/2 = 50%, and 4.0 imply 1/4 = 25%.
What do American odds mean?
A positive figure like +150 is the profit on a 100 stake. A negative figure like −200 is the stake needed to win 100. The tool converts both to a percentage automatically.
Why don’t bookmaker odds add up to 100%?
Real-world odds include a margin (the ‘overround’ or vig), so implied probabilities across all outcomes sum to more than 100%. This tool shows the raw implied probability of the odds you enter, before any margin.
Is this gambling advice?
No. It is a maths converter for understanding and comparing odds formats. It does not predict outcomes or recommend any wager.