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MasterMath

Odds Calculator

Convert odds between the three formats and read what they mean: the probability the bookmaker is assigning, and what you would collect if you win.

Implied probability

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Implied probability—
In decimal format—
In fractional format—
In American format—
You would win—
You would collect in total—

How this was worked out

    Indicative result. The implied probability is not the real probability of the event: it has the bookmaker's margin built in, and that margin always works against the bettor. Only stake what you can afford to lose.

    The formula

    implied probability = 1 ÷ decimal odds × 100

    Where it comes from

    Decimal odds are a multiplier on the stake, with the stake itself included in the return: at 2.50, ten pounds return twenty-five. Their inverse is the probability the bookmaker attaches to the event, though inflated, because the commission is folded into it.

    How to work it out by hand

    1. Convert the odds to decimal format if they are in another
    2. Divide 1 by the decimal odds
    3. Multiply by 100 to express it as a percentage

    What is worth knowing

    The three formats say the same thing three ways. Decimal, standard across Europe, includes the return of the stake. Fractional, the British convention, expresses only the profit: 3/2 means three of profit for every two staked. American uses the sign: +150 is what you win staking 100, and −200 is what you must stake to win 100. Worth remembering that in any real market these probabilities add up to more than 100 %, and the excess is the bookmaker's margin.

    Frequently asked questions

    What do odds of 2.50 mean?

    That every unit staked returns 2.50 if you win, the stake included. The bookmaker is assigning it a 40 % chance.

    How do I turn odds into a probability?

    Divide 1 by the decimal odds. Odds of 4.00 come to 25 %.

    What is the difference between decimal and fractional odds?

    Decimal includes the return of the stake and fractional shows only the profit. Odds of 3.00 are 2/1 fractional.

    What do +150 and −200 mean?

    +150 is what you win staking 100. −200 is what you must stake to win 100.