How to Read Betting Odds: American, Decimal & Implied Probability
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Odds tell you two things at once: how much a bet pays, and how likely the book thinks the outcome is. Once you can read them fluently, line shopping — taking the best available price on each bet — becomes second nature.
This guide covers the three formats you will see, how to turn any price into an implied probability, and why a half-point of price improvement matters more than most bettors realise.
American odds
American odds are quoted with a plus or minus sign. A negative number is the amount you must stake to win $100; a positive number is the amount you win on a $100 stake.
So -160 means risk $160 to win $100, and +135 means risk $100 to win $135. The favourite carries the minus sign, the underdog the plus.
Decimal odds
Decimal odds express your total return per $1 staked, including your stake back. Decimal 2.35 returns $2.35 for every $1 — a $1.35 profit.
To convert American to decimal: for positive odds, divide by 100 and add 1; for negative odds, divide 100 by the absolute value and add 1.
Implied probability
Every price implies a probability. Convert it and you can compare two books — or a sportsbook against a prediction market — on the same scale.
For negative American odds, implied probability = odds / (odds + 100). For positive odds, it = 100 / (odds + 100). A -160 favourite implies about 61.5%; a +135 underdog implies about 42.6%.
The vig, and why shopping matters
Add up the implied probabilities on both sides of a market and you get more than 100%. That overage is the hold — the book’s built-in margin, also called the vig or juice.
Because every book sets its own prices, the best available number on a given side moves around. Taking the best price on each bet shrinks the vig you pay and, over a season, is the single biggest edge most bettors can control.
Frequently asked questions
- What do + and − mean in betting odds?
- A minus sign marks the favourite and shows how much you must stake to win $100 (e.g. -160 = risk $160 to win $100). A plus sign marks the underdog and shows the profit on a $100 stake (e.g. +135 = win $135 on $100).
- How do I convert odds to a probability?
- For negative American odds, divide the odds by (odds + 100). For positive odds, divide 100 by (odds + 100). The result is the implied probability the price represents.
- Why are the best odds different at each sportsbook?
- Each book prices independently and shades lines toward its own customers’ betting patterns. That is why the best number on a side varies book to book, and why OddsGrab lines them up so you can take the top price.
- What are fractional odds?
- Fractional odds (e.g. 7/2) are common in the UK and horse racing. The number on the left is the profit, the number on the right is the stake: 7/2 returns $7 profit for every $2 staked. Divide and add 1 to convert to decimal — 7/2 is decimal 4.5.
- How much does a better price actually matter?
- A lot, over time. Moving from -115 to -105 on a bet you make often turns a long-term loss into a near break-even. Because the gain compounds across every wager, consistently taking the best price is the highest-leverage habit a bettor has.
- What is a “fair” price with no vig?
- De-vigging removes the book’s margin so both sides of a market sum to 100%. Compare the de-vigged number to the price you can actually get: if a book offers better than fair, that is positive expected value.
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Educational content for informational purposes only. Not betting or financial advice. Please gamble responsibly. 21+ where applicable.