Implied probability is the percentage chance that a betting price says an outcome has. For American odds, divide 100 by (odds + 100) when the odds are positive. When they are negative, divide the odds (without the minus sign) by (odds + 100). So +110 implies 47.6%, and -110 implies 52.4%. Below you get the formulas for all three odds formats, a quick-reference chart, the step most guides skip (removing the sportsbook’s margin), and how to use the result to judge value.
TL;DR
- Positive American odds: 100 ÷ (odds + 100). Negative: odds ÷ (odds + 100). Decimal: 1 ÷ odds. Fractional: denominator ÷ (numerator + denominator).
- +110 is 47.62%. -110 is 52.38%. Both sides of a -110/-110 market add up to 104.76%, and that extra 4.76% is the sportsbook’s margin.
- Raw implied probability includes the vig. Divide each side by the total to get a no-vig (fair) probability.
- A number is useful only when you compare it with your own estimate or with the market’s other prices.
- If you need this for hundreds of games, an odds API can return the numbers for you.
Table of Contents
- What implied probability tells you
- How to calculate implied probability from American odds
- Decimal and fractional odds
- Quick-reference chart
- Why both sides add up to more than 100%
- How to remove the vig and get a no-vig probability
- Turning a percentage back into odds
- Using implied probability to find value
- Doing it at scale
- Promo: no-vig probabilities in one request
- Perspective
- FAQ
- Sources
What implied probability tells you
Every price on a betting board carries a built-in claim about how likely the outcome is. Sporting News describes implied probability as the percentage chance the sportsbook believes the outcome needs to have, based on the price. Another way to read it: it is the break-even win rate. If you bet at +150 and the true chance is exactly 40%, you neither gain nor lose over time.
That is why converting odds into percentages puts a market in perspective. You can see how likely the book thinks one outcome is relative to the others, instead of trying to compare -135 with +120 by feel.
One caution before the math: the percentage is “implied” by the price, not guaranteed by anything. It blends the book’s opinion, the money it has taken and its own margin.
How to calculate implied probability from American odds
American odds are the format on most US sportsbooks, and they come in two flavors.
Positive odds (underdogs)
The number tells you the profit on a $100 stake. The formula is:
Implied probability = 100 ÷ (odds + 100)
The Smarkets help centre shows +450 as 100 ÷ (450 + 100) = 18.1%. The same logic gives:
- +110: 100 ÷ 210 = 0.4762, or 47.62%
- +180: 100 ÷ 280 = 0.357, or 35.7%
- +800: 100 ÷ 900 = 11.1%
Negative odds (favorites)
The number tells you how much you must stake to win $100. The formula is:
Implied probability = odds ÷ (odds + 100), using the odds without the minus sign
Smarkets uses -500 as 500 ÷ 600 = 83.3%. Others:
The +110 question
A +110 price means you win $110 on a $100 bet. Plug it in: 100 ÷ (110 + 100) = 47.62%. You need to win about 47.6% of the time to break even. A -110 price is the mirror image at 52.38%, which is why standard point spreads and totals priced at -110 on both sides are the baseline most bettors know.
Decimal and fractional odds
If you read international markets or compare across formats, these two are short.
Decimal odds: Implied probability = 1 ÷ decimal odds. Boss of Betting gives 1.50 as 66.67% and 3.00 as 33.33%. Odds of 4.00 imply 25%, and 2.50 implies 40%.
Fractional odds: Implied probability = denominator ÷ (numerator + denominator). Fractional 5/2 gives 2 ÷ 7 = 28.57%, and 1/4 gives 4 ÷ 5 = 80%, per the same Boss of Betting guide. A 7/5 price is 5 ÷ 12 = 41.7%, which matches decimal 2.40 and American +140. A +300 price equals 3/1 and implies 25%.
Quick-reference chart
You can memorize a handful of these and estimate the rest.
| American odds | Decimal | Fractional | Implied probability |
|---|---|---|---|
| -300 | 1.33 | 1/3 | 75.00% |
| -200 | 1.50 | 1/2 | 66.67% |
| -150 | 1.67 | 2/3 | 60.00% |
| -110 | 1.91 | 10/11 | 52.38% |
| +100 | 2.00 | 1/1 | 50.00% |
| +110 | 2.10 | 11/10 | 47.62% |
| +150 | 2.50 | 3/2 | 40.00% |
| +200 | 3.00 | 2/1 | 33.33% |
| +300 | 4.00 | 3/1 | 25.00% |
| +500 | 6.00 | 5/1 | 16.67% |
Why both sides add up to more than 100%
In a fair two-way market, the two implied probabilities would sum to exactly 100%. Sportsbooks price them so the sum is higher. The excess is the vig, also called juice or margin.
Take the standard -110/-110 market: 52.38% + 52.38% = 104.76%. The extra 4.76% is the book’s built-in edge.
Legal Sports Report offers an NBA example: Celtics -310 is 75.6% and Heat +245 is 28.9%, a total of 104.5%. Neither team has a 104.5% chance of winning, so the raw numbers overstate both sides.
How to remove the vig and get a no-vig probability
The simplest method is proportional: divide each side’s implied probability by the total.
- Convert both prices to implied probability.
- Add them together.
- Divide each one by that sum.
Worked example with the Celtics -310 and Heat +245:
- Celtics: 75.6% ÷ 104.5% = 72.3%
- Heat: 28.9% ÷ 104.5% = 27.7%
Those two add to 100%, and they are a better estimate of the market’s real view. With -110/-110, each side becomes 52.38 ÷ 104.76 = 50%.
This proportional approach is the simplest, not the only one. Some bettors weight the margin more heavily onto longshots, so treat the no-vig figure as a close estimate rather than an exact truth. For a market with three outcomes, such as soccer 1X2, the steps are the same: add all three, then divide each one.
Turning a percentage back into odds
Going the other way is handy when you build your own fair price.
- If your probability p is 50% or higher, American odds = -(p ÷ (1 - p)) × 100. At 60%: -(0.6 ÷ 0.4) × 100 = -150.
- If p is below 50%, American odds = ((1 - p) ÷ p) × 100. At 40%: (0.6 ÷ 0.4) × 100 = +150.
- Decimal odds = 1 ÷ p. At 40%, that is 2.50.
Using implied probability to find value
Investopedia notes that comparing the bookmaker’s implied probability with your own estimate shows whether a wager offers value. It also reminds you that odds include a margin and do not reflect true chances. So the process looks like this:
- Estimate the true chance from a model, power ratings or a no-vig market consensus.
- Convert the book’s price to implied probability.
- If your number is higher than the price implies, the bet has positive expected value on paper.
Example: you rate a team at 45%. A book offers +140, which implies 100 ÷ 240 = 41.7%. The 3.3-point gap is your estimated edge. At +110 (47.6%), you would pass, because the price needs more than you believe the team has.
The same idea works from the other side: if you find a team with a low implied probability that you think is primed for an upset, that is how value bettors find their spots.
What makes a percentage worth acting on
A gap is only meaningful if your estimate is good. Three checks help:
- Compare to the no-vig market, not the raw price. A 2-point edge against the vigged number can vanish once you remove the margin.
- Shop several books. The same game can be +105 at one book and +120 at another. That is 48.8% versus 45.5% implied, a real difference on the same outcome.
- Track the close. If the price you took tends to be better than the final price, your estimates are probably sound. Our guide on closing line value walks through how to measure it.
For building a repeatable process, see how to build your own +EV tool.
Doing it at scale
A calculator is fine for one bet. It breaks down when you want to compare a dozen books on every game, every night. You can do the same arithmetic in a spreadsheet, and our walkthrough on a sports betting model in Excel with live odds shows how. If you would rather skip the formulas, an API can return the numbers already calculated.
Promo: no-vig probabilities in one request
PingOdds aggregates odds from 14 US and Ontario sportsbooks into a single JSON API, with current prices, historical price changes and no-vig probabilities. You get the best available price across books without writing a scraper for each one. The Free plan costs $0 per month, Starter is $19 per month and Pro is $99 per month. Paid plans add higher request limits, live streaming, advanced betting signals, webhooks and AI agent integrations. Our data is timestamped and our data quality is the same on every tier. See the Free, Starter and Pro plans or start from the PingOdds odds API.
If you are comparing tools first, our guide to choosing an odds comparison site covers what matters.
Perspective
Most implied probability mistakes come from one habit: treating the raw percentage as the truth. It is the price with the margin still inside it. The moment you compare two books, or compare a book with your own model, that margin changes the answer.
We built PingOdds around that idea. When 14 sportsbooks sit in one response, with timestamps showing how fresh each price is, you can see the spread of implied probabilities for the same outcome and compute a no-vig number from the whole market. Price history adds the part a calculator cannot: how a probability moved, and when.
We keep data quality the same on every tier, because a clean implied probability is only useful if the price under it is current. The percentage is the start of the analysis, and the market around it is where the value shows up.
Cameron
FAQ
What is a good implied probability percentage?
There is no universally good number. It is good when it is lower than your honest estimate of the outcome’s chance, because that means the price pays more than the risk requires. A 40% implied probability is a bargain on a team you rate at 45% and a poor price on one you rate at 35%.
What is the implied probability of -110 odds?
It is 110 ÷ 210 = 52.38%. You need to win just over 52.4% of your bets at -110 to break even. The same price on both sides of a market totals 104.76%, which is the vig.
How do I calculate implied probability from moneyline odds?
For a favorite (negative odds), divide the odds without the minus sign by that number plus 100. For an underdog (positive odds), divide 100 by the odds plus 100. So -150 gives 60%, and +150 gives 40%.
Is implied probability the same as true probability?
No. The raw figure includes the sportsbook’s margin, so two sides of a market add up to more than 100%. Dividing each side by the total gives a no-vig estimate that is closer to the market’s view, though still only an estimate.
Sources
- Sporting News: how to read betting odds
- Legal Sports Report: what is implied probability
- Smarkets Help Centre: how to calculate implied probability
- Boss of Betting: implied probability guide
- bettingexpert Academy: how to convert odds
- BetMGM blog: what is implied probability
- SBO.net: what is implied probability
- Investopedia: understanding betting odds