Implied Probability Calculator - Convert Betting Odds
Convert American, Decimal, or Fractional betting odds to implied probability percentage instantly — the essential tool for sports betting value analysis.
Select the odds format, enter the odds, and click Calculate to see the implied probability and equivalent odds in all three formats.
Implied Probability Calculator - Convert Betting Odds
Convert American, Decimal, or Fractional betting odds to implied probability percentage instantly — the essential tool for sports betting value analysis.
Negative odds (e.g. -150) denote the favourite; positive odds (e.g. +250) denote the underdog. Used primarily in North American sports betting.
About the Implied Probability Calculator
Implied probability is the conversion of betting odds into a percentage that represents the bookmaker's assessment of the likelihood of a particular outcome. When a sportsbook sets odds, it is effectively expressing a probability. Understanding how to convert between odds formats and implied probability is the foundational skill of value betting — identifying markets where the true probability of an outcome exceeds the bookmaker's implied probability.
American odds, also called moneyline odds, are the dominant format in North American sports betting. Negative American odds indicate the favourite and show how much you must stake to win $100 profit. For example, odds of −150 mean you risk $150 to win $100, and the implied probability is 150 / (150 + 100) = 60%. Positive American odds indicate the underdog and show how much profit a $100 stake earns. Odds of +250 mean a $100 stake wins $250 profit, and the implied probability is 100 / (250 + 100) = 28.57%. The two sides of a two-outcome market should ideally sum to 100%, but bookmakers build in an overround (or vig) so the sum of implied probabilities typically exceeds 100%, ensuring a margin regardless of the outcome.
Decimal odds, also called European odds, express the total return per unit staked including the original stake. Odds of 1.75 mean that for every $1 bet, you receive $1.75 back (a profit of $0.75). The implied probability is simply 1 / decimal odds = 1 / 1.75 ≈ 57.14%. Decimal odds greater than 2.00 correspond to positive American odds (underdogs), and decimal odds between 1.00 and 2.00 correspond to negative American odds (favourites). Decimal odds below 1.00 are not offered because they imply a guaranteed loss — the sportsbook would be paying you less than your stake.
Fractional odds, the traditional British format, express the ratio of profit to stake. Odds of 5/2 mean you win $5 for every $2 staked, so a $2 bet returns $7 total. The implied probability is denominator / (numerator + denominator) = 2 / (5 + 2) = 28.57%, the same as +250 American or 3.50 decimal. Odds of 1/1 are called 'evens' and imply a 50% probability.
The overround is the sum of all implied probabilities in a market minus 100%. A typical two-outcome market might have implied probabilities of 52% and 52%, summing to 104% — the extra 4% is the bookmaker's built-in edge. Removing the overround (dividing each implied probability by the sum and multiplying by 100%) gives the 'fair' probability the market assigns to each outcome. Value betting means finding outcomes where your estimated true probability exceeds the bookmaker's fair probability — those bets have positive expected value over the long run.
The implied probability calculator converts between all three major formats in both directions, so you can instantly compare odds from different bookmakers expressed in different formats, identify the highest value offer, and track whether a line has moved toward or away from your estimate of the true probability.
Implied Probability Examples
Click an example button to load the values into the calculator.
| Odds | Implied Probability | Context |
|---|---|---|
| American -150 (favourite) | 60.00% | The bookmaker implies a 60% chance of this outcome. You must risk $150 to profit $100. |
| American +250 (underdog) | 28.57% | Only a 28.57% implied chance of winning, but a $100 stake returns $250 profit if correct. |
| Decimal 1.75 | 57.14% | Standard European format. A €1 stake returns €1.75 total. Equivalent to -133 American. |
| Fractional 5/2 | 28.57% | Classic UK horse racing odds. Win $5 for every $2 staked. Equivalent to +250 American or 3.50 decimal. |
| Decimal 2.00 (evens) | 50.00% | Even money — the bookmaker implies a coin-flip chance. Equivalent to +100 American or 1/1 fractional. |
How to Use the Implied Probability Calculator
- Select the Odds Format used by your sportsbook: American (moneyline), Decimal (European), or Fractional (UK).
- Enter the odds value. For American odds, enter a negative number for favourites (e.g. -150) or a positive number for underdogs (e.g. +250). For Decimal, enter the multiplier (e.g. 1.75). For Fractional, enter the numerator and denominator separately (e.g. 5 and 2 for 5/2).
- Click Calculate Probability. The result shows the implied probability as a percentage plus the equivalent odds in all three formats.
- Compare the implied probability to your own estimate of the true probability. If your estimate exceeds the implied probability, the bet has positive expected value.
- Use the example buttons to quickly load common odds scenarios and verify your understanding of the conversion formulas.
Implied Probability FAQ
What is implied probability in betting?
Implied probability is the conversion of the bookmaker's odds into a percentage that represents the likelihood the bookmaker assigns to an outcome. For odds of -150, the implied probability is 60% — meaning the bookmaker's model suggests the outcome will occur 60% of the time. It is called 'implied' because it is derived from (implied by) the odds rather than from a direct probability estimate.
Why do the implied probabilities of all outcomes in a market sum to more than 100%?
Bookmakers build in an 'overround' or 'vig' — a margin that ensures they profit regardless of the result. In a two-outcome market with implied probabilities of 55% and 52%, the sum is 107%; the extra 7% is the bookmaker's edge. Removing the overround by dividing each probability by the total and rescaling to 100% gives the 'no-vig' or 'fair' probability. Finding a bet whose fair probability exceeds the no-vig probability is the definition of a value bet.
How do I convert American odds to decimal odds?
For positive American odds: decimal = (American / 100) + 1. For example, +250 becomes (250/100) + 1 = 3.50. For negative American odds: decimal = (100 / |American|) + 1. For example, -150 becomes (100/150) + 1 ≈ 1.667. The calculator performs these conversions automatically and shows all three formats simultaneously.
What are 'even money' odds?
Even money (also written 'evens') means the profit equals the stake. In American odds that is +100; in decimal odds it is 2.00; in fractional odds it is 1/1. The implied probability of evens is exactly 50%. A fair coin flip would be offered at evens by a bookmaker without a margin.
Is a lower or higher implied probability better for a bettor?
A lower implied probability corresponds to higher odds, meaning a larger potential payout relative to the stake. However, 'better' depends entirely on your assessment of the true probability. A bet at +500 (implied probability ~16.7%) is a good bet if you believe the true probability is, say, 25%. The same bet is poor value if the true probability is only 10%. Comparing your estimated probability to the implied probability is the core of value betting.
Can decimal odds ever be below 1.00?
No. Decimal odds represent total return per unit staked including the stake itself, so odds of 1.00 would return exactly your stake with zero profit — and odds below 1.00 would return less than your stake. In practice, the lowest decimal odds offered are around 1.01, representing an implied probability of about 99% for an overwhelming favourite.