Every set of betting odds represents a percentage chance of winning. This is called Implied Probability. To be a successful bettor, you must compare this “Implied %” against your own estimation of the outcome.
Use our free tool to instantly convert betting odds into their percentage form. This is the first step in finding “Value Bets.”
How to Calculate Implied Probability
The math changes depending on the odds format used by your bookmaker. Here are the formulas our calculator uses:
1. Decimal Odds (e.g., 2.50)
This is the simplest format used in Europe and Canada.
Formula:
(1 / Decimal Odds) * 100
Example: Odds of 2.00 implies a 50% chance (1 / 2.0 = 0.50).
2. American Odds (e.g., -110 or +150)
Used in the USA. The formula differs for favorites (-) and underdogs (+).
- Negative (-):
Odds / (Odds + 100) * 100 - Positive (+):
100 / (Odds + 100) * 100
Example: -150 implies 60% probability. +150 implies 40% probability.
3. Fractional Odds (e.g., 5/2)
Common in the UK and Horse Racing.
Formula:
Denominator / (Numerator + Denominator) * 100
Example: 3/1 odds implies a 25% chance.
Why Does Implied Probability Matter?
Understanding this number allows you to calculate Expected Value (EV). If you believe a team has a 60% chance to win, but the bookmaker’s odds imply only a 52% chance, you have found a “Value Bet.”
Note on the Vig: If you convert the odds for both sides of a game (e.g., Team A and Team B) and add the percentages together, the total will usually be over 100% (e.g., 104.5%). This extra percentage is the “Vig” or “Juice”—the bookmaker’s fee.