In sports betting, the odds displayed by a bookmaker do not represent the actual chance of an event happening. They represent the Implied Probability plus a hidden fee known as the “vig,” “juice,” or “margin.”
To find value in the market, you must look past the sticker price. Our Gambling Probability Calculator does the math for you. It converts odds into percentages and performs a “Devig” (De-vigorish) calculation to strip away the bookmaker’s margin, revealing the True Probability and the Fair Odds of the event.
Probability & Devig Calc
How to Use the Probability Calculator
This tool is essential for checking if a bet offers positive expected value (+EV). Here is how to interpret the numbers:
- Select Market Type:
- 2-Way: For markets with two outcomes (e.g., Tennis Match Winner, NFL Spreads, Over/Under).
- 3-Way: For markets with a Draw option (e.g., Soccer 1X2, Hockey Regulation Time).
- Enter the Odds: Input the decimal odds for all outcomes. You must enter odds for both (or all three) sides of the bet to calculate the margin accurately.
- Analyze the “True Prob”:
- Implied %: This is what the odds say the probability is (inflated).
- True Prob %: This is the realistic probability after removing the casino’s fee.
- Check the Margin: The tool will display the total “Vig.” If the margin is negative (e.g., -1.5%), the calculator will alert you to a Surebet (Arbitrage) opportunity.
Real-World Examples: Implied vs. True Probability
Why do you need a probability calculator for gambling? Because bookmakers manipulate the numbers. Here is the difference between what you see and what is real.
Example 1: The “Coin Flip” (NBA Spread)
You are betting on an NBA Point Spread. Both teams are listed at odds of 1.91 (-110).
- Implied Probability: 1 ÷ 1.91 = 52.36%.
- The Reality: Mathematically, both teams cannot have a 52% chance of winning; that adds up to 104.7%.
- The Devig Result: The calculator removes the 4.7% margin. The True Probability is 50.00%. This confirms that to be profitable at these odds, you must win more than 52.36% of your bets.
Example 2: The Heavy Favorite (UFC)
A UFC fighter is a favorite at 1.33, and the underdog is 3.40.
- Implied Probabilities: Favorite (75.2%) + Underdog (29.4%) = 104.6% Total.
- Calculator Result:
- True Probability (Favorite): 71.9% (Fair Odds: 1.39)
- True Probability (Underdog): 28.1% (Fair Odds: 3.56)
- Analysis: If you think the favorite actually wins 80% of the time, the bet has value. If you think they win 72% of the time, the bet is a loser, even though they are likely to win.
Frequently Asked Questions (FAQ)
What is the difference between Implied and True Probability?
Implied Probability is the percentage chance suggested by the bookmaker’s odds (1 divided by Decimal Odds). It is always inflated to include the house edge. True Probability is the actual statistical chance of the event occurring, calculated by removing that house edge (devigging).
What is “Devigging”?
Devigging is short for “De-vigorishing.” It is the mathematical process of removing the bookmaker’s fee (vig) from a set of odds to find the “Fair Odds” (the price a sportsbook would offer if they took zero profit).
Why do the probabilities add up to more than 100%?
This is called the Overround or Bookmaker’s Margin. In a fair market, all outcomes would sum to 100%. In betting, they usually sum to 104-108%. The extra percentage is the bookie’s theoretical profit margin if they balance their book perfectly.
What does it mean if the margin is negative?
If the gambling probability calculator shows a negative margin (e.g., Total Probability = 98%), you have found an Arbitrage Bet (Surebet). This means the odds are so high on both sides that you can bet on every outcome and guarantee a profit regardless of who wins.