Guide

Implied probability, fair price and value

Updated 12 November 2026 · 3 min read

Implied probability is 1 divided by the decimal odds. Across all the results of a match those chances add up to more than 100 %, and the extra is the bookmaker's margin. Divide each chance by the total and you have the market's fair chances and fair prices. A bet has value when your chance times the price is more than 1.

Implied probability

Every price implies a chance: 1 divided by the decimal odds. A price of 2.00 implies 50 %, a price of 4.00 implies 25 % and a price of 1.25 implies 80 %. Fractional and American prices work the same once they are turned into decimal; the odds converter does that for you.

The bookmaker's margin

Price a coin toss fairly and each side is 2.00. A bookmaker prices both sides lower, say 1.91 each, and keeps the difference. Add up the implied chances of every result in a market and the total is above 100 %. The excess is the margin, also called the overround.

The margin in a football match
Result	Price	Implied chance	Fair chance	Fair price
Home win	2.10	47.6 %	45.4 %	2.20
Draw	3.40	29.4 %	28.1 %	3.56
Away win	3.60	27.8 %	26.5 %	3.77
Total		104.8 %	100 %

Here the implied chances total 104.8 %, so the margin is 4.8 %.

Finding the fair price

To take the margin out, divide each implied chance by the total. For the home win, 47.6 % ÷ 104.8 % = 45.4 %. The fair price is one over that fair chance: 1 ÷ 0.454 = 2.20. These are the market's own estimate of each result with the bookmaker's cut removed. This simple method spreads the margin evenly across the results; sharper methods put more of it on the longer prices, but the idea is the same.

A fair price is the price at which a bet would break even over many bets, if the chance were right.

What value means

A bet has value when its price is higher than the fair price for the true chance. Value is your chance multiplied by the price, less 1.

You make a result 50 % likely and the price is 2.20: 0.50 × 2.20 - 1 = +10 %. Over many such bets you would expect to win 10 % of what you stake.
At 1.90 the same bet is worth 0.50 × 1.90 - 1 = -5 %: a loser, although the result is just as likely.

Value depends on the chance being right, and chances are estimates. A bet with value on paper can still lose, and often does; value is about the long run, not the next match.

Why a likely bet is not always a good bet

A result that is 80 % likely is not a good bet at a price of 1.20, because it breaks even at 1.25. How likely a bet is tells you how often it wins; value tells you whether the price pays enough for it. Our tips need both: a likely market at a price better than its fair price. How it works has the rule in full.

Try it

The odds converter turns any price into a chance, and the value screen sets prices against our chances (the prices open with membership).

Questions

How do you calculate implied probability?

Divide 1 by the decimal odds. For fractional odds, turn them into decimal first (divide the fraction and add 1); for American odds, +150 is 2.50 and -150 is 1.67.

What is the overround?

The total of the implied chances of every result in a market, which is always above 100 %. The amount above 100 % is the bookmaker's margin.

What is a fair price?

One over the true chance of a result. It is the price at which a bet would break even over many bets. When a bookmaker pays more than the fair price, the bet has value.

How do I know whether a bet has value?

Multiply your chance by the decimal price and take away 1. If the answer is above zero, the bet has value, but only if your chance is right.