The overround is the bookmaker's guaranteed profit margin, hidden inside the odds. Every market has one — the question is how big.

To calculate it, convert each outcome's odds to implied probability and sum them. A two-way market at 1.91/1.91 has a 104.7% overround — the book keeps 4.7%.

Sharp bettors shop for the lowest overround because it directly determines long-term profitability. A 2% margin versus 5% is the difference between winning and losing over a season.

Enter any market's odds below to reveal the true margin instantly.