Divide 1 by the decimal odds and multiply by 100: odds of 2.20 give 45.45%. That percentage comes from the displayed price, so it still contains the bookmaker's margin and says nothing certain about the true probability of the outcome.
What is an implied probability?
Implied probability is the chance of success that a price assumes. Put another way: what probability would make these odds fair? It doesn't answer the question "how likely is this outcome?"
The word "implied" says it all. Nobody measured it or pulled it out of a model. It's tucked inside the price, flaws included. The operator's margin comes first, then any estimation errors it may have made.
What is the implied probability formula?
With decimal odds, divide 1 by the odds, then multiply by 100.
implied probability (%) = (1 ÷ decimal odds) × 100
Odds of 2.00 give 50%. Odds of 1.80 give 55.56%. Odds of 5.00 give 20%. When the odds go up, the implied probability goes down. It's mechanical: one is the inverse of the other.
Convert odds into an implied probability
Enter decimal odds and a stake. Both the comma and the point are accepted.
Comma or dot accepted: 2,20 as well as 2.20.
Only used to illustrate the return. Nothing is stored.
Result
- Implied probability
- 45.45%
- Gross return
- €22.00
- Net profit
- €12.00
Warning:
Implied probability is derived from the displayed odds: it still contains the bookmaker margin. It does not describe the real probability of the outcome.
A table of examples
Common odds, their implied probability and the return on a £10 stake. The gross return includes the stake. The net profit only counts what's added on top of what you staked.
| Odds | Calculation | Implied probability | Gross return | Net profit |
|---|---|---|---|---|
| 1.50 | 1 ÷ 1.50 | 66.67% | £15.00 | £5.00 |
| 1.80 | 1 ÷ 1.80 | 55.56% | £18.00 | £8.00 |
| 2.00 | 1 ÷ 2.00 | 50.00% | £20.00 | £10.00 |
| 2.20 | 1 ÷ 2.20 | 45.45% | £22.00 | £12.00 |
| 3.40 | 1 ÷ 3.40 | 29.41% | £34.00 | £24.00 |
| 5.00 | 1 ÷ 5.00 | 20.00% | £50.00 | £40.00 |
Watch the return. Decimal odds pay out with the stake included. Odds of 2.20 don't "double" your stake: they multiply it by 2.2, and 1 of that is your stake coming back.
In this table, the 2.00 row is my anchor: 50%, and a net profit equal to the stake. The other rows read relative to it.
A real case: Parma v AS Roma (Serie A). In the case table below, the last column converts each margin-free price into a probability using the same formula (1 ÷ odds). When the odds fall, the probability rises. The chart shows how the odds on a Roma win moved over the 7 days before this match, now finished.
From 3 May to the start, the margin-free odds on “AS Roma win” moved from 1.85 to 1.53 (−17.23%), a margin-free probability of 54.02% then 65.27%. Lowest value seen: 1.53; highest: 1.89. This chart describes a past market movement: it says nothing about the match result and is not betting advice.
| Outcome | First tracked odds | Last odds before the start | Change | Margin-free probability (first, then last) |
|---|---|---|---|---|
| Parma win | 4.88 | 7.91 | +62.28% | 20.51% then 12.64% |
| Draw | 3.93 | 4.53 | +15.25% | 25.46% then 22.09% |
| AS Roma win | 1.85 | 1.53 | −17.23% | 54.02% then 65.27% |
Source: OddScore. Margin-free odds computed from the odds of the international reference bookmakers, snapshots from 3 May to 10 May 2026, match already played. Data frozen on 11 October 2026.
How do you do the reverse calculation?
To go from a probability back to odds, divide 1 by that probability written as a fraction. At 50%, 1 ÷ 0.50 = 2.00. At 45.45%, you get 2.20 back.
This reverse calculation has a name when the probability comes from somewhere other than the bookmaker: fair odds, covered in our fair odds guide. The difference matters. Inverting the implied probability of some odds just takes you back to where you started. Inverting an independent estimate gives you new information, which you can compare with the displayed price.
What implied probability does not mean
Three misreadings come up all the time.
First, it isn't the true probability of the outcome. It comes from a commercial price. Nobody observes the real probability of a sporting event, before the match or after it: a game played once doesn't reveal the distribution it came from.
Next, it still contains the margin. Add up the implied probabilities of every outcome in a match and the total goes above 100%. Each probability on its own is therefore a little overstated. To compare two bookmakers on a common basis, take that excess out first. That's what margin-free odds are for.
Finally, it flags no value. An implied probability of 45.45% says nothing about whether a bet is worth taking. To talk about theoretical value you need a second estimate that doesn't come from the odds, explained on value bet.
Why does the total go above 100%?
Because the bookmaker's margin is spread across every price in the market. With odds of 1.80 and 2.00, the implied probabilities add up to 105.56%. The 5.56 points above 100% are the overround.
That excess is why an implied probability always sits a little higher than the estimate behind it. The full calculation, the difference between overround and theoretical margin, and the reasons it varies from one market to another are on bookmaker margin.
The same conversion, margin removed, is also what puts a value on a free bet. The free bet calculator applies it to a bet whose stake isn't returned.
Calculate the margin of a full market →
What OddScore does with this conversion
OddScore continuously converts the odds of several bookmakers, then removes each one's margin before any comparison. Without that, you'd be comparing two prices loaded in different ways. A low-margin operator would always look more "cautious" than a high-margin one, for reasons that have nothing to do with its sporting estimate.
The conversion is the first link in the chain. What matters next is how it moves over time and how consistent it is across operators. The guide on odds movements covers both.
In short. Implied probability shows what a price assumes. It lets you estimate the gap between two prices once the margin is removed. It doesn't let you conclude that an outcome will happen.
Put it into practice
Apply this guide to real odds.
See a market reading
A real match with its odds, movements and 0-100 signal.
Open the demoMargin calculator
Measure a bookmaker's margin on any market.
Calculate the marginDig into the market
Odds movements are only part of the story. Here are the next topics to read.
Odds and probability: the complete guide
The full journey, from the displayed odds to the closing line.
Read the guideBookmaker margin: definition and calculation
Why the implied probabilities add up to more than 100%.
Understand the marginMargin-free odds: the proportional method
Spreading the overround back out so you can compare two operators on a common basis.
Remove the marginFair odds: from an estimated probability to a price
The reverse calculation, applied to an estimate that doesn't come from the bookmaker.
Calculate fair oddsFrequently asked questions
How do you calculate an implied probability?
Divide 1 by the decimal odds, then multiply the result by 100. Odds of 2.50 give an implied probability of 40%.
What is the implied probability of odds of 2.20?
45.45%, which is 1 divided by 2.20. With £10 staked, a winning bet would return £22, including £12 of net profit.
Is the implied probability the true probability of the outcome?
No. It comes from a price that includes a commercial margin. Nobody can observe the true probability of a sporting event, before or after the match.
Why do the implied probabilities of a match add up to more than 100%?
Each one carries a share of the bookmaker's margin. The total, called the book percentage, almost always sits above 100%. The excess is the overround.
How do you get the odds back from a probability?
Divide 1 by the probability written as a fraction. A probability of 50% gives odds of 2.00, and 40% gives odds of 2.50.
Does the odds format change the implied probability?
No. Decimal odds of 2.50 are written 3/2 in fractional format and +150 in American format. All three describe the same price, so the implied probability is 40% either way.
Sources & methodology
This page draws on the standard formula for converting decimal odds, on economic research into the overround and betting-market prices, and on OddScore's own odds-analysis method. The UK Gambling Commission and BeGambleAware are listed as the regulator and the player-support service.
- Convert the decimal odds into an implied probability (1 ÷ odds), without removing the margin first.
- Calculate the gross return of a stake (odds × stake) and the net profit (gross return − stake).
- Point out every time that the probability you get still contains the operator's margin.