Convert between fractional, decimal and American odds — edit any format and the rest update instantly.
Odds
Type into whichever format you have — the others convert automatically.
Payout
Fractional odds are shown as the closest standard betting fraction, so they can round very slightly against an exact decimal.
About this calculator
The three formats all describe the same thing in different ways. Decimal odds show your total return per unit staked, so 2.50 means a £1 bet returns £2.50 in total. Fractional odds show profit against stake, so 3/2 means £3 profit for every £2 staked. American odds show how much profit a 100 stake makes on a positive line (+150), or how much you must stake to profit 100 on a negative line (−200).
Implied probability is simply 1 ÷ decimal odds, expressed as a percentage — it's the chance of winning that the price corresponds to. Converting to implied probability is the quickest way to compare prices across bookmakers, because it puts every format on the same scale.
Add up the implied probabilities of every outcome in a market and you'll usually get more than 100%. That excess is the bookmaker's margin (the overround or vig) — the built-in edge that means the odds offered are shorter than the true chances.
This is a maths tool for converting prices, not betting advice. Odds reflect a bookmaker's pricing, including their margin, rather than a true probability of any outcome.
Frequently asked questions
How do I convert odds to a probability?
Divide 1 by the decimal odds and multiply by 100. Decimal odds of 2.50 give 1 divided by 2.5, which is 40% implied probability.
What do American odds like +150 and -200 mean?
A positive line is the profit on a 100 stake, so +150 returns 150 profit for 100 staked. A negative line is the stake needed to profit 100, so -200 means risking 200 to make 100.
Why do the probabilities in a market add up to more than 100%?
That excess is the bookmaker's margin, often called the overround or the vig. It means the prices offered are slightly shorter than the true chances, which is where the bookmaker's edge comes from.