How betting markets work
Before you can find good bets, you need the language of betting. This lesson explains the three ideas that appear in every single bet: the odds (the price), the chance they hide (probability) and the fee the book charges (the vig).
Odds are the price of a bet
Odds do two jobs: they say who the book thinks will win, and how much you get paid. American odds use a minus sign for the favorite: -150 means you bet 150 to win 100. They use a plus sign for the underdog: +150 means you bet 100 to win 150. The minus side is the one the book thinks is more likely to win.
Turn odds into a chance (percentage)
Any odds can become a 'how likely is this really' percentage. For a favorite like -150: take the number (150), divide by itself plus 100 → 150 ÷ 250 = 60%. For an underdog like +150: 100 ÷ (100 + 150) = 40%. That 60/40 is the book's opinion of the game in numbers.
The vig is the book's fee
If you add both chances — 60% + 40% — you get 100%. Real books often show a total above 100%, like 104%. The extra 4% is the vig: the fee the house charges for accepting your bet, a bit like a bank's exchange rate. Strip that fee out and you have the 'true' chances, which is what you compare your own opinion against.