What Is Implied Probability? Bookmaker Margin Explained
Understand implied probability and how bookmakers build their margin into odds. Learn to calculate the overround and find value bets.
What Is Implied Probability?
Every set of betting odds contains an implied probability — the bookmaker's mathematical estimate of how likely an outcome is.
The Formula
Implied Probability = 1 ÷ Decimal Odds × 100%
Example: Premier League Match
OutcomeOddsImplied Probability |---------|------|---------------------| Home Win2.1047.6% Draw3.4029.4% Away Win3.8026.3% Total103.3%
The total exceeds 100% by 3.3 percentage points — this is the bookmaker's margin, also called the overround.
Why the Total Exceeds 100%
In a fair market, all implied probabilities would sum to exactly 100%. The excess above 100% represents the bookmaker's built-in profit margin. A 103.3% overround means the bookmaker expects to keep approximately 3.2% of all stakes placed on this market.
Finding Value
A bet has positive expected value when you believe the true probability of an outcome is higher than the bookmaker's implied probability. For example, if you believe the home team has a 55% chance of winning but the bookmaker's implied probability is only 47.6%, that represents potential value.
Use our Odds Calculator to calculate implied probability and overround for any set of odds.
Responsible Gambling: Betting carries financial risk. If you or someone you know needs help, contact Befrienders Kenya: +254 722 178 177. This content is for educational purposes only. You must be 18+ to bet.