Bookmakers usually include a margin in their odds, which gives them a long-term mathematical advantage. I first learned about it when comparing odds for a basketball game. Two sites offered slightly different prices for the same outcome, and it helped me understand why those differences matter.

The margin means the implied probabilities across all possible outcomes usually add up to more than 100%. That extra percentage reflects the bookmaker’s built-in margin, although actual results can vary. If you want to explore related betting terms, you could look at bet in exchange with the explanations of probability and odds. Understanding the numbers can help you make sense of a market, but it doesn’t guarantee a winning bet. I think it’s also worth remembering that bookmakers set their prices to manage risk, not simply to predict the result.