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Definition

Implied Probability

Also known as Break-Even Percentage, Implied Odds

By Reviewed Editorial policy

In short

Implied probability is the chance of an outcome suggested by its odds. Divide 1 by decimal odds: a price of 4.00 implies 25%. It always overstates the real probability, because the bookmaker's margin is built in.

Implied probability converts a price into a percentage. It is the most useful single calculation in betting, because it turns “is 3.75 a good price?” into “do I think this is more likely than 26.7%?”, a question you can actually answer.

The calculation

From decimal odds: 1 ÷ odds

  • 2.00 → 50%
  • 3.75 → 26.7%
  • 10.00 → 10%

From American odds:

  • Positive: 100 ÷ (odds + 100)
  • Negative: |odds| ÷ (|odds| + 100)

From fractional odds: denominator ÷ (numerator + denominator)

  • 5/1 → 1 ÷ 6 = 16.7%
  • 5/2 → 2 ÷ 7 = 28.6%

It is always too high

This is the part that matters. Implied probability is not the bookmaker’s estimate, it is the estimate plus margin.

Price a football match 2.10 / 3.40 / 4.00 and the implied probabilities are 47.6%, 29.4% and 25.0%. They sum to 102.0%, which is impossible. The 2% excess is the overround.

Every individual price is therefore inflated. The bookmaker does not think the home side is 47.6%, it thinks something slightly lower, and has shaded the price to build in profit. Recovering the underlying estimate means stripping the margin out proportionally, which is devigging.

Using it

Implied probability gives you a break-even threshold. At 3.75 you need the outcome to happen more than 26.7% of the time to profit.

So the question becomes concrete: do I believe this is more likely than the price implies? If you think a team is a genuine 33% chance and the price implies 26.7%, that is a positive expected value bet, regardless of whether it wins.

Two cautions. First, your own estimate needs to beat the devigged market price, not the raw implied figure, because the raw figure is already padded in your favour as a threshold. Second, the market’s estimate aggregates an enormous amount of information and money. Disagreeing with it is easy; being right to disagree is not.

Common questions

How do I work out implied probability?

Divide 1 by the decimal odds. A price of 4.00 implies 25%. For American odds use 100 divided by the odds plus 100 for positives, or the absolute odds divided by that same total for negatives.

Why do implied probabilities add up to more than 100%?

Because the bookmaker's margin is built into every price. The excess above 100% is the overround, and it means each individual price overstates the real chance. Stripping it out is called devigging.

Is implied probability the bookmaker's real estimate?

No, it is the estimate plus margin. The book thinks the outcome is somewhat less likely than the price suggests. To find the underlying view you have to remove the overround proportionally across all outcomes.

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