Free tool

The odds converter (decimal, fractional, American)

Change any of the 4 fields and the rest update instantly. Useful when a bookmaker uses a different format from the one you are used to.

The format used across Latin America, Europe and most online bookmakers.
The traditional British format, written as 5/2 or 11/10.
The US format: +150 for underdogs, −200 for favourites.
What the odds say the chance is, with the bookmaker margin included.

The three formats, and why they coexist

The same price can be written three ways. Decimal odds (2.50) show what you get back per unit staked, stake included. Fractional odds (3/2) show the net profit against the stake. American odds show how much you win on 100 (+150) or how much you have to risk to win 100 (−200).

Implied probability, the number that matters

Whatever the format, the useful conversion is to probability: 1 / decimal odds. It lets you compare a price against your own estimate, and compare bookmakers that quote in different formats.

💡 Add up the implied probabilities of every outcome in a market and you will get more than 100%. That excess is the bookmaker's margin — the overround. The smaller it is, the better the price you are getting.

How to use this converter

  1. Type into whichever field matches the format your bookmaker shows.
  2. The other three update on the spot, including the implied probability.
  3. Compare that probability with your own estimate. If yours is higher, check the bet in the EV calculator.
  4. To size the stake, use the Kelly calculator.

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