The hold calculator measures the sportsbook's built-in margin on a market by combining the implied probabilities from the listed odds. To use it, choose the odds format and enter the prices for each side of the market, such as both sides of a spread or moneyline, and the calculator will return the hold percentage. For example, if both sides of a two-way market are priced at -110, the calculator will show a hold of about 4.76%, which reflects the bookmaker's margin. It is a simple way to compare market quality and see when pricing is tighter or more expensive across books.