Odds Converter
Decimal, fractional, American and the probability behind all three.
Convert Odds. Decimal, fractional, American and the probability behind all three. Shows the working, not just the answer.
Implied probability
25%
4 decimal · +300 American · 3 : 1 against
Odds and probability are the same information in different clothes. Decimal odds are the total return per unit staked, so 4.0 means a 25% chance. Fractional odds are profit to stake, so 3/1 is the same 25%. American odds show what a 100 stake wins, or what you must stake to win 100. "Implied probability" is the phrase to watch. Bookmakers' quoted odds imply probabilities that sum to more than 100% across all outcomes, and that excess is the margin. Comparing your own estimate against the implied figure is the whole of value betting. This converts between notations exactly. It does not remove the margin, predict anything, or tell you a bet is good.
How the Odds Converter works
Convert between probability and the three odds notations, in any direction. Odds and probability carry the same information — the notations differ only in what they measure against, which is why the same chance looks like 4.0, 3/1 and +300.
Also known as: odds to probability · decimal odds to american · what does plus 300 mean · implied probability from odds
Frequently asked questions
How do I convert odds to probability?
For decimal odds, divide 1 by the odds — 4.0 is a 25% chance. For fractional odds a/b, the probability is b divided by (a+b), so 3/1 is one in four. Both give the same answer for equivalent odds.
What are American odds?
A positive number is the profit on a 100 stake, so +300 means winning 300 from 100. A negative number is the stake needed to win 100, so −200 means staking 200 to win 100. Values between −100 and +100 do not exist.
What is implied probability?
The probability the quoted odds correspond to. Across all outcomes of an event, a bookmaker's implied probabilities sum to more than 100%, and that excess is the margin — the reason odds are not a neutral estimate.
Do better odds mean a better bet?
Only relative to the real probability. Long odds on an outcome less likely than they imply is a bad bet; short odds on something more likely than they imply is a good one. Comparing your own estimate against the implied figure is the entire method.
Why are odds written differently in different places?
Convention. Fractional is traditional in British horse racing, decimal is standard across Europe and in exchanges, and American is used in US sportsbooks. They are the same numbers in different clothes.
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