Convert betting odds between decimal, fractional, American (moneyline) and implied probability. Type into any field and the rest update instantly — everything runs in your browser.
Tip: a stake of 100 units at these odds returns — (including stake).
All odds formats describe the same thing — the payout relative to the stake, and the probability the price implies. The cleanest way to convert is to route everything through decimal odds, then translate out to the other formats.
Decimal odds of 2.50 imply 100 / 2.50 = 40%.
2.50 → 1.50 → 3/2. Fractional odds show profit only, which is why you subtract the stake (the “− 1”).
2.50 → +150. A price of 1.50 → −200.
| From | Formula → decimal |
|---|---|
| American (+) | (American / 100) + 1 |
| American (−) | (100 / |American|) + 1 |
| Fractional a/b | (a / b) + 1 |
| Implied p% | 100 / p |
Implied probability is the chance of an outcome suggested by its odds. It is useful because it lets you compare a price against your own estimate: if you think an outcome is more likely than the implied probability, the bet has positive expected value.
One caveat: bookmaker odds include a margin (the “overround”), so the implied probabilities of all outcomes in a market add up to more than 100%. To get the “fair” probability you would need to remove that margin — a separate calculation.
Subtract 1 from the decimal odds and express the result as a fraction. For example, 3.50 becomes 2.50, which is 5/2.
If the decimal odds are 2.00 or higher, multiply (decimal − 1) by 100. If they are below 2.00, divide −100 by (decimal − 1).
Because bookmaker prices include a built-in margin. The extra percentage above 100% across all outcomes is the overround, which is roughly the bookmaker's edge on the market.
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