Overround Calculator
Calculate market overround, market maker margin, and fair odds
Market Odds
Results
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 market. In a perfectly fair market, the overround would be exactly 100%. However, market makers build in a margin, 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 market maker's margin.
Formula: Overround = (1/Odds₁ + 1/Odds₂ + ... + 1/Oddsₙ) × 100
Understanding Market Maker Margins
The market maker margin (Overround - 100%) represents the built-in margin taken by the party on the other side of the market. Different markets and market makers have varying margins based on regulation, competition, and market liquidity.
Excellent (0-5%)
Premium exchanges, sharp market makers, highly liquid markets. Great value for traders.
Good (5-10%)
Competitive market makers, popular markets. Reasonable value, worth considering.
Average (10-15%)
Standard retail market makers, regulated markets. Typical for mainstream trading.
Poor (15%+)
Novelty markets, low liquidity events, or predatory market makers. Avoid if possible.
Why Calculate Overround?
Identify Fair Odds
Lower overround means better value and fairer odds for traders
Compare Market Makers
See which market makers offer the most competitive margins
Calculate Fair Odds
Remove the margin to find the true probability and fair odds
Spot Opportunities
Find markets where market makers have made pricing errors
Overround in Regulated Markets
In highly regulated 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 market maker 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%
Market Maker Margin = 5.29%