How to Read Moneyline Odds and Implied Probability
Learn to read American moneyline odds in minutes: what + and − mean, how to convert odds into win probability, and how to spot the vig.
Money-line odds are the foundation of sports betting, yet the plus and minus signs confuse almost everyone at first. Once you understand what they represent, you can read any board instantly — and, more importantly, judge whether a price is fair.
What the minus sign (−) means
A negative number is the favorite and tells you how much you must stake to win $100. At -150, you risk $150 to win $100. The bigger the number, the heavier the favorite.
What the plus sign (+) means
A positive number is the underdog and tells you how much you win on a $100 stake. At +150, a $100 bet wins $150. The bigger the number, the bigger the underdog — and the larger the potential payout.
Converting odds to implied probability
Every price maps to an implied probability — the win rate you would need just to break even. The formulas are quick:
- Favorite (−): probability = odds ÷ (odds + 100). Example: 150 ÷ 250 = 60%.
- Underdog (+): probability = 100 ÷ (odds + 100). Example: 100 ÷ 250 = 40%.
If you think a +150 underdog actually wins more than 40% of the time, you have found value — the price is paying you more than the real risk.
Spotting the vig (the sportsbook’s cut)
Add the two implied probabilities on a game and you will usually get more than 100%. That extra slice is the vigorish — the book’s built-in margin. On a -110 / -110 game, each side implies about 52.4%, totaling 104.8%. That 4.8% is the house edge you are fighting, which is why finding value and shopping for the best price matters so much.
Why line shopping pays
Different sportsbooks post slightly different prices on the same game. Consistently taking the best available number — even a few cents better — adds up to a meaningful long-term difference. This is why comparing books before you bet is one of the easiest edges available to any bettor.
Frequently asked questions
- What does +150 mean in betting?
- A +150 money line means the team is an underdog and a $100 bet would win $150 in profit (returning $250 total). It also implies about a 40% chance of winning, calculated as 100 ÷ (150 + 100).
- How do you convert moneyline odds to probability?
- For a favorite (−), divide the odds by the odds plus 100 — so -150 becomes 150 ÷ 250 = 60%. For an underdog (+), divide 100 by the odds plus 100 — so +150 becomes 100 ÷ 250 = 40%.
- What is the vig in sports betting?
- The vig (vigorish) is the sportsbook’s built-in margin. Because the implied probabilities of both sides add up to more than 100%, the extra percentage represents the house edge you must overcome to profit long term.
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