Implied Probability Calculator: Odds to Fair Chance (2026)
Turn any price into the real chance behind it. Enter one outcome to read its implied probability and fair odds, or a whole market to expose the bookmaker margin and the vig-free fair prices the book is really working from.
Implied probability calculator
Enter your odds
One price gives you the implied chance. Add every outcome of a market and you also see the margin and the fair odds.
Result
104.71%
4.71%
The booksum is the total implied probability of every outcome. Anything over 100% is the bookmaker margin, also called the overround or vig.
Proportional: each outcome keeps its share of the book. The simple standard, exact for balanced markets.
| Outcome | Odds | Implied | Fair (no-vig) | Fair odds |
|---|---|---|---|---|
| Outcome 1 | 1.91 | 52.36% | 50.00% | 2.00 |
| Outcome 2 | 1.91 | 52.36% | 50.00% | 2.00 |
Implied probability is the chance baked into a price, margin and all. It is not the true chance of the event. Strip the margin and you get closer, but a fair price is still a market opinion, not a certainty.
Odds to implied probability reference table
Common prices converted to their implied probability. Handy for a quick read without opening the tool.
| Decimal | American | Fractional | Implied probability |
|---|---|---|---|
| 1.20 | -500 | 1/5 | 83.33% |
| 1.50 | -200 | 1/2 | 66.67% |
| 1.80 | -125 | 4/5 | 55.56% |
| 1.91 | -110 | 91/100 | 52.36% |
| 2.00 | +100 | 1/1 | 50.00% |
| 2.50 | +150 | 3/2 | 40.00% |
| 3.00 | +200 | 2/1 | 33.33% |
| 4.00 | +300 | 3/1 | 25.00% |
| 5.00 | +400 | 4/1 | 20.00% |
| 8.00 | +700 | 7/1 | 12.50% |
| 11.00 | +1000 | 10/1 | 9.09% |
| 21.00 | +2000 | 20/1 | 4.76% |
| 51.00 | +5000 | 50/1 | 1.96% |
Each figure is a single-price implied probability, so it still includes the bookmaker margin. Add the outcomes of a real market in the tool above to strip the vig and see the fair chance.
How implied probability works and how to strip the bookmaker margin
Every odds price is a probability in disguise. Learn to read it and you stop seeing numbers and start seeing the chance the bookmaker is charging you for. As of 2026 the sharpest edge available to a recreational bettor is simply understanding what a price really means. This guide covers the formula, the margin hidden in every market, and how to find the fair no-vig chance underneath.
What the ToolsGambling implied probability calculator does
Most odds-to-probability tools convert a single price and stop. This one goes two steps further. Type one price in decimal, American or fractional odds and it shows the implied chance and the fair decimal price. Add every outcome of a market and it sums them into the booksum, reports the exact bookmaker margin, and de-vigs the prices into the fair probabilities the book is really working from.
That de-vig is the part that matters. A raw implied probability always overstates the real chance because it carries the margin. Removing that margin, the vig-free number, is how sharp bettors compare a soft book's line to a fair one and spot where the value hides. This calculator does it for a two-way, three-way or any-way market, live as you type.
What you get here that a plain converter skips:
- ·All three odds formats with live conversion, so you never convert a price by hand.
- ·The full market margin (overround) calculated across every outcome you enter.
- ·Four de-vig methods (multiplicative, additive, power and Shin) for vig-free fair probabilities and fair odds.
- ·A single-price value check that flags whether a line beats your own estimate.
- ·A shareable link, an embeddable widget and an indexable reference table.
It is built for the bettor who wants to see behind the price, not just accept it. Whether you are checking a moneyline, comparing two books, or learning how the margin works, the numbers here are exact and the margin has nowhere to hide.
What implied probability means
Implied probability is the chance of an outcome as expressed by its odds. Decimal odds of 2.00 imply a 50 percent chance. Odds of 4.00 imply 25 percent. It is the bookmaker's own estimate of how likely the outcome is, with the margin already folded in, which is why the numbers across a market add up to more than 100 percent.
The formula
For decimal odds, implied probability is 1 divided by the price, times 100. So 1 divided by 2.50 is 0.40, or 40 percent. American odds split in two: a negative price like -200 is the risk over risk plus 100, and a positive price like +150 is 100 over stake plus 100. The calculator handles all of this the moment you type.
Any odds format works
Decimal, American and fractional all describe the same probability in different clothes. Switch the format at the top and every price converts. To convert a single price between formats on its own, use the odds converter.
The bookmaker margin hidden in every price
No bookmaker offers fair odds. Every price is shaded so the implied probabilities of a market add up to more than 100 percent. That extra slice is the margin, and it is how the book makes money whichever side wins. On a single price you cannot see it. Across a whole market it stands out plainly.
Booksum and overround
Add the implied probability of every outcome and you get the booksum. Subtract 100 percent and what is left is the overround, the margin. A tight two-way market runs around 102 to 105 percent; a soft three-way can top 108. The lower the number, the better the price you are getting. Dig into a single market with the margin calculator.
A worked example
Take a two-way market priced at 1.91 on each side. Each implies 52.36 percent, so the booksum is 104.71 percent and the margin is 4.71 percent. Strip that back to 100 and both outcomes come out at a fair 50 percent, or fair odds of 2.00. That gap between 1.91 and 2.00 is exactly what the bookmaker is charging you.
No-vig fair probability, the number that matters
The vig-free or no-vig probability is what you get after removing the margin so the outcomes add back to 100 percent. It is the market's best guess at the true chance, stripped of the book's cut. Sharp bettors treat the no-vig line from a low-margin book as the closest thing to a fair price, then hunt for soft books offering better.
How the de-vig is calculated here
This calculator gives you four de-vig methods, so you are not stuck with one book's opinion. Multiplicative, the proportional default, divides each implied probability by the booksum. Additive strips an equal slice of margin from every outcome. Power raises each probability to a common exponent, and Shin's model assumes a share of insider money. Power and Shin both shade more of the margin onto longshots, correcting the favorite-longshot bias that the simple method ignores. Switch methods in the tool and watch the fair odds move.
Turning implied probability into value
A value bet exists when your own honest estimate of the chance is higher than the implied probability of the price. If a book prices a team at 2.50, that is a 40 percent implied chance. If you genuinely believe the team wins 45 percent of the time, the price is value and, over many such bets, profitable.
The single-price value check in this tool does exactly that comparison: type your estimated chance and it reports the edge and whether the odds beat it. Confirm the edge, then size the bet with the value bet calculator.
How to use the implied probability calculator on ToolsGambling
Enter your odds
Pick your odds format and type a price. For a single outcome you get the implied chance and fair odds straight away. To analyse a full market, add a row per outcome and enter each price. The result updates live.
Read the margin and the fair odds
With two or more outcomes, the tool shows the booksum, the margin, and a table with each outcome's implied and vig-free fair probability plus its fair price. A high margin means a poor price; a low one means the book is competitive.
Check for value
On a single price, type your own estimated chance in the value field. The calculator flags a positive or negative edge. If the edge is real, size the stake sensibly with the Kelly calculator.
Common mistakes with implied probability
Treating implied probability as the true chance
Implied probability includes the margin, so it always overstates the real chance a little. The number you should compare your own estimate against is the no-vig fair probability, not the raw implied figure.
Ignoring the margin when comparing books
Two books can post the same headline odds while one hides a fatter margin in the other side of the market. Always look at the full booksum, not one price, before deciding who offers the better line.
Forgetting that a fair price is still an opinion
De-vigging removes the margin, not the uncertainty. The fair probability is the market's view, and the market is wrong often enough to matter. When two books disagree sharply, that gap can be a real edge, which the sure bet scanner.
Implied probability terms
- Implied probability
- The chance of an outcome as expressed by its odds. For decimal odds it is 1 divided by the price, times 100.
- Margin (vig, overround)
- The extra built into a market so the implied probabilities add up to more than 100 percent. It is how the bookmaker profits regardless of the result.
- Booksum
- The total implied probability of every outcome in a market. A booksum of 104.7 percent means a 4.7 percent margin.
- No-vig / fair probability
- The implied probability after the margin is removed, so the outcomes add back to 100 percent. The closest the market gets to a true chance.
- Fair odds
- The decimal price that matches a probability with no margin. A 50 percent chance has fair odds of 2.00.
- De-vig
- The process of stripping the margin out of a market to recover the fair probabilities. This tool uses the proportional method.
- Value bet
- A bet where your estimated chance is higher than the price implies, giving a positive expected return over the long run.
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A note on responsible betting
Understanding a price is a tool, not a guarantee. Only stake money you can afford to lose, and never chase a loss. If betting stops being fun, take a break and get support at BeGambleAware.org.
Implied probability FAQ
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Evgeniy Volkov
Verified ExpertFullstack developer with a background in mathematics. I build the calculators and game-style tools on ToolsGambling with Pixi.js and modern web tech, and every result uses transparent probability formulas you can verify yourself.