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Foundation

Odds formats: American, decimal, and fractional

Three notations for the same underlying quantity. Learn to convert between them and to see the implied probability behind each.

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How this lesson runs

  1. 01

    American odds

  2. 02

    Decimal odds

  3. 03

    Fractional odds

Want this applied to a specific price? The Sports.co Analyst walks through the arithmetic. It explains method only — never picks.

Video walkthrough: Odds formats: American, decimal, and fractional

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American odds

A negative number is the stake required to win 100 units. A positive number is the profit on a 100-unit stake. -150 and +150 are not mirror images: the first implies 60% and the second 40%.

Decimal odds

Decimal odds express total return per unit staked, including the stake. 2.50 returns 2.50 for every 1 risked, implying 40%. Implied probability is simply 1 divided by the decimal price.

Fractional odds

Fractional odds express profit relative to stake: 3/2 pays 3 profit for 2 risked. Convert to decimal by dividing and adding one, then invert for probability.

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