Implied Probability Calculator
Convert decimal or American betting odds into implied probabilities and calculate the bookmaker's total margin (overround). Use it to identify which outcomes are overpriced and assess the book's built-in edge.
About this calculator
Implied probability is the likelihood of an outcome as priced into betting odds. For decimal odds, the formula is: Implied Probability = 1 / decimalOdds × 100%. For a two-outcome market (home and away), the total implied probability is: Total = (1/homeOdds) + (1/awayOdds). For three outcomes including a draw: Total = (1/homeOdds) + (1/awayOdds) + (1/drawOdds). In a fair market, the total would equal exactly 100%. Any excess above 100% is the bookmaker's margin (overround), representing their built-in profit. For example, a total of 107% means the book holds a 7% margin. The calculator outputs each outcome's implied probability and the aggregate total, so you can compare bookmaker pricing with your own probability estimates to identify value bets.
How to use
A soccer match has Home odds = 2.10, Draw odds = 3.40, Away odds = 3.60 (decimal format). Step 1 — Enter all three odds and select 'decimal' format. Step 2 — Home: 1/2.10 = 47.62%. Step 3 — Draw: 1/3.40 = 29.41%. Step 4 — Away: 1/3.60 = 27.78%. Step 5 — Total implied probability = 47.62 + 29.41 + 27.78 = 104.81%. The bookmaker's margin is 4.81% — meaning the true fair odds are slightly longer than listed.
Frequently asked questions
How do I calculate implied probability from decimal betting odds?
To calculate implied probability from decimal odds, divide 1 by the decimal odds and multiply by 100. For example, decimal odds of 2.50 give an implied probability of (1/2.50) × 100 = 40%. This means the bookmaker is pricing the outcome as if it has a 40% chance of occurring. If you believe the true probability is higher than 40%, the bet has positive expected value relative to those odds.
What is bookmaker margin and how does it affect my bets?
Bookmaker margin (also called overround or vig) is the extra probability built into odds that ensures the book profits regardless of outcome. It is calculated as the total implied probability across all outcomes minus 100%. A 5% margin on a two-outcome market means that for every $100 in bets, the book expects to keep $5. This directly reduces your expected return — the higher the margin, the worse the expected value for the bettor. Comparing margins across bookmakers helps you find the most favorable prices.
When should I use implied probability to find value bets?
Implied probability is most useful when you have an independent estimate of an outcome's true likelihood. If you assess the true probability of a team winning at 55% but the bookmaker's implied probability is only 45%, there is a perceived edge of 10 percentage points. Over a large number of bets where your assessments are accurate, backing outcomes where your estimated probability exceeds the implied probability produces a positive expected return. Tracking your predictions against actual results over time is critical to validating whether your estimates are genuinely better than the market.