How to Read Betting Odds
What Are Betting Odds?
Betting odds represent two things at once: the probability of an outcome occurring and how much you stand to win if your bet is correct. Understanding how to read odds is the single most important skill for any sports bettor, yet many bettors place wagers without fully grasping what the numbers mean.
American Odds (Moneyline Format)
American odds are the standard format used by U.S. sportsbooks. They come in two flavors:
- Negative odds (-110, -150, -300) tell you how much you need to risk to win $100. At -110, you risk $110 to win $100. At -300, you risk $300 to win $100. The larger the negative number, the heavier the favorite.
- Positive odds (+150, +200, +500) tell you how much you win on a $100 bet. At +150, a $100 bet returns $150 in profit. At +500, a $100 bet returns $500. The larger the positive number, the bigger the underdog.
A common mistake is thinking -110 means you lose $110. You risk $110, but if you win, you get back your $110 stake plus $100 profit — a total return of $210.
Decimal Odds
Popular in Europe and Australia, decimal odds show your total return per $1 wagered, including your stake. Decimal 2.50 means a $100 bet returns $250 total ($150 profit + $100 stake). To convert American to decimal:
- Positive American: (odds / 100) + 1 — so +150 becomes (150/100) + 1 = 2.50
- Negative American: (100 / |odds|) + 1 — so -200 becomes (100/200) + 1 = 1.50
Fractional Odds
Used primarily in the UK, fractional odds like 3/2 mean you win $3 for every $2 risked. A 3/2 fractional line is equivalent to +150 American or 2.50 decimal. You'll rarely encounter fractional odds at American sportsbooks, but they appear frequently in horse racing.
Understanding Juice (Vig)
The vig — short for vigorish, also called juice — is the sportsbook's built-in commission. The standard vig on spread and totals bets is -110 on both sides. If the true probability of each side were exactly 50%, fair odds would be +100 (even money). By charging -110, the sportsbook collects roughly 4.5% margin on every dollar wagered regardless of the outcome.
This is why beating the closing line matters. A bettor who consistently gets +EV odds before the line moves is extracting value despite the vig. Our prediction model specifically looks for edges large enough to overcome the standard juice.
Implied Probability
Every odds line implies a probability of that outcome occurring. This is critical for identifying value bets — situations where you believe the true probability exceeds what the odds suggest.
- Negative American: Implied probability = |odds| / (|odds| + 100) — so -150 implies 150/250 = 60%
- Positive American: Implied probability = 100 / (odds + 100) — so +200 implies 100/300 = 33.3%
- Decimal: Implied probability = 1 / decimal odds — so 2.50 implies 1/2.50 = 40%
Note that the combined implied probability of both sides always exceeds 100% — that gap is the vig. If both sides are -110, the combined implied probability is 52.4% + 52.4% = 104.8%. The 4.8% overround is the sportsbook's edge.
Putting It Together
When you see a line like Duke -6.5 (-110), it means Duke is favored by 6.5 points and you must risk $110 to win $100. The implied probability of Duke covering is 52.4%. If your analysis — or a data-driven model like ours — suggests Duke covers more than 52.4% of the time in this spot, that's a value bet worth considering.
Ready to see odds analysis in action? Check our prediction results to see how our model performs against the market.