What is implied probability?

It is the chance of winning that a price represents: 1 divided by the decimal odds. Odds of 4.00 imply a 25% chance.

Why do the percentages in a market add up to more than 100%?

The extra amount is the bookmaker's margin, or overround. In a two-way market priced 1.91 / 1.91 the implied probabilities total 104.7%, so 4.7 percentage points belong to the bookmaker.

Fair odds are the break-even price for a given probability, with no margin attached: 100 ÷ your percentage. A 40% chance has fair decimal odds of 2.50.

How do I know if a bet has value?

Compare your own probability estimate with the price's implied probability. If you believe the chance is higher than the price implies, the bet has positive expected value — assuming your estimate is right, which is the hard part.

Implied Probability Calculator

Implied probability is what a price says about the chance of an outcome. Convert odds into a percentage below, or go the other way and turn your own estimate into the fair price you would need.

Odds to probability

Odds format

Odds

Implied probability

40.00%

Includes the bookmaker's margin.

Expressed as

1 in 2.5

How often the price says this lands.

Probability to fair odds

Your probability estimate (%)

Fair decimal odds

2.50

Break-even price with no margin.

Fair American

+150

Fair fractional

3/2

The formulas

implied probability = 1 ÷ decimal odds × 100

fair decimal odds = 100 ÷ probability%

market total = sum of every outcome's implied probability

fair probability = outcome probability ÷ market total

Only the last line removes the margin, and it needs every outcome in the market — a single price cannot tell you the bookmaker's true estimate.

Odds and the chance they imply

Implied probability across the range of common prices.
Decimal odds	Implied probability	Roughly
1.10	90.91%	9 times in 10
1.50	66.67%	2 times in 3
2.00	50.00%	a coin flip
3.00	33.33%	1 time in 3
5.00	20.00%	1 time in 5
10.00	10.00%	1 time in 10
21.00	4.76%	1 time in 21
51.00	1.96%	1 time in 51

Common mistakes

Treating implied probability as truth. It is the price's view with margin included, not a measured frequency.
Comparing your estimate against the raw implied figure. Strip the margin out first with the bookmaker margin calculator.
Assuming a small edge is real. A 1–2 percentage-point difference is usually inside the error bars of your own estimate.

Frequently asked questions

Last reviewed: 24 August 2026. Formulas on this page are checked against the unit test suite that powers every bet.ing calculator.