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Odds
Converter.
Odds Converter: What is this price in decimal, fractional and American odds, and what chance does it imply? Enter two figures and this page returns implied probability of this price, with every line of the arithmetic printed rather than hidden. The worked example below answers 40.00% for the figures it states. Free to embed. Checked 2026-08-23.
Run it on your numbers40.00%
01Run it on
Run it on
your numbers.
The fields open holding the worked example below, and the answer changes as you change them. Every line of the arithmetic is printed under the result, and the formula under that — so the answer can be checked rather than trusted.
Implied probability of this price40.00%The arithmetic,
The arithmetic,
line by line.
| Step | Value |
|---|---|
| Decimal | 2.500 |
| Fractional | 3/2 |
| American | +150 |
| Implied probability | 40.00% |
| Returns per 1 staked, stake included | 2.50 |
decimal = 1 + (fraction as a decimal), or 1 + American ÷ 100, or −100 ÷ American + 1 probability = 100 ÷ decimal fractional = decimal − 1, as the nearest conventional fraction American = (decimal − 1) × 100 when decimal ≥ 2, otherwise −100 ÷ (decimal − 1)
02The worked example,
The worked example,
in plain HTML.
| Input | Value | What it is |
|---|---|---|
| Notation you are entering | American — +150 | Decimal is standard in Europe and on most crypto books; fractional in the UK and Ireland; American on US-facing books. |
| The price | +150 | Type it exactly as the book shows it. A fraction takes a slash; an American price takes its sign. |
| Implied probability of this price | 40.00% | Computed by the same function the calculator above runs. The build refuses to publish this page if the two disagree. |
+150 is 2.50 in decimal, 3/2 in fractional, and says the outcome has a 40.00% chance. That last number is the one to argue with: back it only if you think the real chance is above 40%. Add up the implied probabilities of every outcome in a market and the total will exceed 100% — the excess is the book's margin, and it is what you are paying to be there.
WHAT THIS CANNOT TELL YOUWhere the answer
Where the answer
stops being one.
Every calculator on this site ends here, because the number at the top is only as good as what it leaves out — and what it leaves out is never nothing.
| Limit | What it means |
|---|---|
| What this cannot see | A price is what the book will pay, not what will happen. Implied probability is the chance the price corresponds to before the book's margin is removed, so it always overstates the true chance the book itself believes in. Fractional output is the nearest conventional fraction rather than an exact one, because bookmakers price in a fixed ladder of fractions; the decimal figure beside it is the exact one. |
| What it is not | Arithmetic, not advice. Nothing on this page recommends gambling, gambling more, or taking any particular bet, and no calculator turns a negative expectation into a positive one. |
03Put this on
Put this on
your own site.
Free, no account, no charge and no script of ours on your page. The snippet loads the calculator on its own in an inert frame, and keeps an attribution link outside it in your markup.
05Questions about
Questions about
this calculator.
What is this price in decimal, fractional and American odds, and what chance does it imply?
+150 is 2.50 in decimal, 3/2 in fractional, and says the outcome has a 40.00% chance. That last number is the one to argue with: back it only if you think the real chance is above 40%. Add up the implied probabilities of every outcome in a market and the total will exceed 100% — the excess is the book's margin, and it is what you are paying to be there.
What can the odds converter not tell me?
A price is what the book will pay, not what will happen. Implied probability is the chance the price corresponds to before the book's margin is removed, so it always overstates the true chance the book itself believes in. Fractional output is the nearest conventional fraction rather than an exact one, because bookmakers price in a fixed ladder of fractions; the decimal figure beside it is the exact one.
Is the odds converter free to use and embed?
Yes. There is no account, no sign-up and no charge, the page works with JavaScript switched off, and the embed snippet on this page may be pasted into any site. The only thing asked in return is that the attribution link outside the frame is left in place.
Where this arithmetic comes from, and what it is worth.
The formula is printed in full on this page so it can be checked rather than taken. Solaspins asserts no figure of its own here: every number is either one you typed or one derived from it, and the worked example is generated by the same function the form runs. Last checked 2026-08-23. This is arithmetic — not financial, legal or gambling advice.