Sports betting odds tell you two things at once: how much you can win on a wager, and the price the sportsbook is charging for that bet. Once you can read odds in any format, you can compare books, estimate payouts quickly, and move on to more advanced ideas like implied probability and expected value.
This guide covers American odds (most common in U.S. sportsbooks), decimal odds (popular globally), and fractional odds (still used in some markets and horse racing).
American Odds: Favorites vs Underdogs
American odds use plus and minus numbers centered around an even-money baseline of +100.
Negative odds (favorites) show how much you must bet to win $100 in profit. For example, -150 means you risk $150 to win $100 profit (total return $250).
Positive odds (underdogs) show how much profit you would make on a $100 bet. For example, +130 means a $100 bet wins $130 profit if it wins (total return $230).
Quick payout formulas (American)
- Underdog (+ odds): Profit = stake × (odds / 100)
- Favorite (− odds): Profit = stake × (100 / absolute odds)
Decimal Odds
Decimal odds represent total return per unit staked, including your original stake. For example, 2.50 means you get back $2.50 for every $1 wagered (profit of $1.50).
To convert American to decimal:
- Positive American +X: Decimal = (X / 100) + 1
- Negative American −Y: Decimal = (100 / Y) + 1
Decimal odds make it easy to compare prices across markets and to multiply odds for parlays (multiply decimals, then subtract 1 for profit-only if needed).
Fractional Odds
Fractional odds (e.g., 5/2, 4/7) express profit relative to stake. 5/2 means you win $5 profit for every $2 risked. Even money is 1/1 or “evens.”
Implied Probability: From Price to Percentage
Every set of odds implies a win probability before accounting for the sportsbook’s margin (vig). Converting odds to implied probability helps you ask: “Does this price match my view of the game?”
For positive American odds +X: implied probability = 100 / (X + 100) × 100%.
For negative American odds −Y: implied probability = Y / (Y + 100) × 100%.
No-vig (“fair”) probabilities require adjusting both sides of a market—covered in depth in our guide on expected value betting. Tools like PropFinder help you compare implied probabilities across books without manual math.
Line Shopping: The Habit Behind Better Prices
Odds are not identical at every sportsbook. Shopping for the best line on the same bet is one of the simplest ways to improve long-term results. Even half a point on a spread or a few cents of juice on a moneyline adds up over hundreds of bets.
Related guides
Frequently Asked Questions
What is the difference between odds and probability?
Odds are a price. Probability is your estimate (or the market’s estimate) of how often an outcome occurs. Sportsbooks embed a margin in their odds so that the implied probabilities sum to more than 100% across all outcomes in a market.
Are positive odds always “better value”?
Not automatically. A +200 underdog is not inherently a good bet—it only becomes valuable if your fair probability of winning is high enough relative to the price. That is the core of +EV thinking.
Why do U.S. books show American odds by default?
It is convention for the domestic market. Most bettors can switch to decimal in account settings if they prefer.
Is sports betting legal everywhere in the U.S.?
Regulation varies by state. Always verify local rules and only use licensed operators where applicable.
Bet responsibly. If you or someone you know needs help, resources are available through the National Council on Problem Gambling.