For fractional format, enter it with a slash, like "5/1" or "3/2". For American format, the "+" sign before a positive number is optional.
Result
This page has no server side at all. The table you paste is parsed by JavaScript inside your own browser, the chart is drawn on a canvas element on your machine, and the export file is assembled locally. Nothing is uploaded, stored or written to any log. You can disconnect from the network after the page has loaded and everything will still work — which is the simplest way to verify the claim yourself.
Facts and limits of this method
| Decimal formula | probability = (1 / odds) × 100% |
|---|---|
| Fractional a/b formula | probability = (b / (a + b)) × 100% |
| American (+) formula | probability = (100 / (odds + 100)) × 100% |
| American (−) formula | probability = (|odds| / (|odds| + 100)) × 100% |
When it misleads you
- The result is the "implied" probability baked into the odds, not the objective probability of the event — bookmaker odds include a margin (overround), so the implied probabilities of all outcomes of an event usually add up to more than 100%.
- Decimal odds must be greater than 1 — odds equal to or below 1 don't make sense (they would mean a guaranteed loss with no possible win).
- For the fractional format, the first number is the net profit per unit staked, the second is the stake itself; for example, 5/1 means winning 5 units for every 1 unit staked.
- Rounding is applied only to the displayed result — internal calculations use the full precision of JavaScript floating-point numbers.
How it is calculated
For decimal odds, probability is computed as 100% divided by the odds themselves — the higher the odds, the lower the implied probability.
For fractional odds a/b (such as 5/1), probability is computed as b / (a + b), multiplied by 100%.
For positive American odds (such as +150, an underdog bet), probability is computed as 100 / (odds + 100), multiplied by 100%.
For negative American odds (such as −200, a favorite bet), probability is computed as the absolute value of the odds divided by (absolute value of the odds + 100), multiplied by 100%.
Questions and answers
Why do the probabilities of all outcomes usually add up to more than 100%?
Because odds include the bookmaker's margin (overround) — their built-in profit; this causes the implied probabilities of all possible outcomes to sum to more than 100%, rather than exactly 100%.
What do positive and negative American odds mean?
Positive odds (such as +150) show how much you'd win on a 100-unit stake — used for less likely outcomes; negative odds (such as −200) show how much you'd need to stake to win 100 units — used for more likely outcomes (favorites).
How do I enter fractional "evens" odds (1/1)?
Enter it as "1/1" — this corresponds to an implied probability of 50%.
Is my data sent anywhere?
No, the whole calculation runs in your browser.