Overround Calculator
Calculate market overround, bookie margin, and fair odds
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Enter odds to calculate overround
What is Overround?
Overround (also called the "book percentage" or "vigorish") is the total implied probability of all outcomes in a betting market. In a perfectly fair market, the overround would be exactly 100%. However, bookmakers build in a margin to guarantee profit, resulting in an overround above 100%.
For example, if a coin flip had odds of 1.90 for both heads and tails, the overround would be 105.26% ((1/1.90 + 1/1.90) × 100). The extra 5.26% is the bookmaker's margin.
Formula: Overround = (1/Odds₁ + 1/Odds₂ + ... + 1/Oddsₙ) × 100
Understanding Bookie Margins
The bookie margin (Overround - 100%) represents the bookmaker's built-in profit. Different markets and bookmakers have varying margins based on regulation, competition, and market liquidity.
Excellent (0-5%)
Premium exchanges, sharp bookmakers, highly liquid markets. Great value for bettors.
Good (5-10%)
Competitive bookmakers, popular markets. Reasonable value, worth considering.
Average (10-15%)
Standard retail bookmakers, regulated markets. Typical for mainstream betting.
Poor (15%+)
Novelty markets, low liquidity events, or predatory bookmakers. Avoid if possible.
Why Calculate Overround?
Identify Value
Lower overround means better value and fairer odds for bettors
Compare Bookmakers
See which bookmakers offer the most competitive margins
Calculate Fair Odds
Remove the margin to find the true probability and fair odds
Spot Opportunities
Find markets where bookmakers have made pricing errors
Overround in Regulated Markets
In highly regulated betting markets, overround typically averages around 10-15% due to licensing requirements, taxes, and operational costs.
Typical Overround by Market:
- •Premier League Football: 105-108% (highly competitive, lots of liquidity)
- •Horse Racing (UK): 110-120% (varies by race quality and field size)
- •Tennis (ATP/WTA): 105-110% (two-outcome markets, efficient pricing)
- •Lower League Football: 110-115% (less liquidity, higher margins)
- •Novelty/Specials: 120-150%+ (low liquidity, high uncertainty)
How to Use This Calculator
Enter the odds for all possible outcomes in a market. The calculator will show you the overround percentage, the bookmaker's margin, and the fair odds (with margin removed) for each selection.
Example: Football Match
Home: 2.10, Draw: 3.40, Away: 3.60
Overround = (1/2.10 + 1/3.40 + 1/3.60) × 100 = 105.29%
Bookie Margin = 5.29%