How to use the implied probability calculator
- Select the odds format: American, decimal or fractional.
- Type the odds into the first field. You can also type a percentage like
55%to convert a probability back to odds. - Read the implied probability and the equivalent odds in all three formats.
- To find the bookmaker margin, enter the odds for the second (and optionally third) outcome.
- The overround appears below the individual probabilities, showing the bookmaker's built-in edge.
How implied probability is calculated
The implied probability is the break-even win rate that an oddsmaker builds into a line. The formula depends on the format.
For American odds, negative values represent favorites. The formula is -odds / (-odds + 100). For example, -110 gives 110 / (110 + 100) = 110 / 210 = 0.52381, or 52.381%. Positive values represent underdogs: 100 / (odds + 100). So +150 gives 100 / 250 = 0.40, or 40%.
For decimal odds, divide one by the number: 1 / 2.50 = 0.40.
For fractional odds written as A/B, the formula is B / (A + B). Odds of 5/2 give 2 / (5 + 2) = 2/7 = 0.28571, or 28.571%.
Understanding the bookmaker margin (overround)
If you add up the implied probabilities for every outcome in a market, the total exceeds 100%. That excess is the bookmaker margin, also called the overround or vig. It represents the theoretical profit the book holds if action is balanced perfectly.
Consider an NFL point spread where both sides are priced at -110. Each side has an implied probability of 52.381%. Adding them together gives 104.762%. The margin is 104.762% minus 100%, which equals 4.762%. In practice, bettors need to win about 52.38% of their spread bets just to break even because of this margin.
Three-way markets, such as soccer match odds (home win, draw, away win), typically carry a higher overround. If the decimal odds are 2.10, 3.40 and 3.60, the implied probabilities are 47.619%, 29.412% and 27.778%. Their sum is 104.809%, giving a margin of 4.809%.
Converting probability back to odds
This implied probability calculator works in reverse too. If you know a team wins 60% of the time, you can find the fair odds with zero margin.
To get decimal odds from a probability p (expressed as a decimal between 0 and 1): 1 / p. For 60%, that is 1 / 0.60 = 1.667.
To get American odds: if p is greater than 0.50, use -100 * p / (1 - p). For 60%: -100 * 0.60 / 0.40 = -150. If p is 0.50 or less, use 100 * (1 - p) / p. For 40%: 100 * 0.60 / 0.40 = +150.
To get fractional odds: express (1 - p) / p as a fraction. For 60%: 0.40 / 0.60 = 2/3, meaning you risk 3 to win 2.
Common odds conversion reference
The table below shows frequently seen odds across all three formats alongside their implied probabilities. Use it as a quick lookup when evaluating lines.
| American | Decimal | Fractional | Implied probability |
|---|---|---|---|
| -500 | 1.20 | 1/5 | 83.333% |
| -200 | 1.50 | 1/2 | 66.667% |
| -110 | 1.909 | 10/11 | 52.381% |
| +100 | 2.00 | 1/1 | 50% |
| +150 | 2.50 | 3/2 | 40% |
| +200 | 3.00 | 2/1 | 33.333% |
| +300 | 4.00 | 3/1 | 25% |
| +500 | 6.00 | 5/1 | 16.667% |
Removing the margin to find true probability
The implied probability includes the bookmaker's margin, so it overstates the actual chance of an outcome. To estimate the true probability, divide each outcome's implied probability by the total sum of all implied probabilities in the market.
Using the -110 / -110 spread example: each side implies 52.381%. The sum is 104.762%. The true probability for either side is 52.381 / 104.762 = 0.50, or exactly 50%. This makes sense because a standard spread is designed to be a coin flip.
For more complex models that account for rare events or count-based outcomes, analysts sometimes turn to tools like the poisson distribution calculator to model goal or point totals before comparing those estimates against the implied probabilities shown here.
Worked examples
Each result below was produced by the same code the tool runs, so you can check your own numbers against them.
| Example | Input | Result |
|---|---|---|
| NFL spread both sides at -110 | Odds format: american; Odds value: -110; Second outcome odds (for margin): -110 | Implied probability: 52.381%; American odds: -110; Decimal odds: 1.909; Fractional odds: 47619/52381; Outcome 2 probability: 52.381%; Total implied probability: 104.762%; Bookmaker margin: 4.762% |
| Decimal odds single market | Odds format: decimal; Odds value: 2.50 | Implied probability: 40%; American odds: +150; Decimal odds: 2.5; Fractional odds: 3/2 |
| Soccer three-way market | Odds format: decimal; Odds value: 2.10; Second outcome odds (for margin): 3.40; Third outcome odds (optional): 3.60 | Implied probability: 47.619%; American odds: +110; Decimal odds: 2.1; Fractional odds: 52381/47619; Outcome 2 probability: 29.412%; Outcome 3 probability: 27.778%; Total implied probability: 104.809%; Bookmaker margin: 4.809% |
| Fractional odds | Odds format: fractional; Odds value: 5/2 | Implied probability: 28.571%; American odds: +250; Decimal odds: 3.5; Fractional odds: 357143/142857 |
FAQ
What does implied probability mean?
Implied probability is the win percentage that betting odds suggest. It accounts for the bookmaker's margin, so it is slightly higher than the true chance of the event occurring.
Why do the implied probabilities add up to more than 100%?
The amount over 100% is the bookmaker margin, also known as the overround or vig. It guarantees the bookmaker a theoretical profit regardless of which outcome wins, provided the money wagered is distributed proportionally.
How do I convert American odds to a percentage?
For negative odds like -150, divide 150 by (150 + 100) to get 0.60, or 60%. For positive odds like +200, divide 100 by (200 + 100) to get 0.333, or 33.333%.
Can I use this tool to find odds from a probability?
Yes. Enter a number followed by a percent sign, such as 65%, into the odds field. The calculator will return the equivalent American, decimal and fractional odds with zero margin applied.
Is my data sent to a server?
No. This implied probability calculator processes everything locally in your browser. Nothing you type is uploaded or stored.
What is a typical bookmaker margin?
For major sports leagues, margins usually range from 2% to 8%. Two-way markets like point spreads tend to sit around 4.5% to 5%, while three-way soccer markets often run 5% to 8%.