What is vig or juice in sports betting?

The vig (vigorish) or juice is the sportsbook's built-in commission. On a standard -110/-110 market, the book keeps roughly 4.5% of every dollar wagered over time. To break even at -110, you need to win 52.4% of your bets. Books earn profit from the vig regardless of outcomes — which is why consistently winning long-term is genuinely difficult.