Key Takeaways
- American odds show how much you win on a $100 bet (positive) or how much you must bet to win $100 (negative)
- Decimal odds represent total return per $1 wagered, including your stake
- Implied probability converts odds into a percentage, representing the market's estimated chance of an outcome
- The gap between implied probability and true probability is where edges live
- Sportsbooks build in a margin (vig/juice), so implied probabilities on both sides add up to more than 100%
American Odds Explained
American odds are the standard format at US sportsbooks. They come in two forms:
Positive Odds (+150, +200, etc.)
Positive odds tell you how much you'd profit on a $100 bet.
+150 means a $100 bet returns $150 in profit (plus your $100 stake back) for a total payout of $250.
The formula: Profit = Stake × (Odds / 100)
Negative Odds (-110, -150, etc.)
Negative odds tell you how much you need to bet to profit $100.
-110 means you must wager $110 to profit $100 (total payout: $210).
The formula: Profit = Stake × (100 / |Odds|)
Quick Reference
| Odds | $100 Bet Profit | Total Payout | |------|-----------------|--------------| | +200 | $200 | $300 | | +150 | $150 | $250 | | +100 | $100 | $200 | | -110 | $90.91 | $190.91 | | -150 | $66.67 | $166.67 | | -200 | $50 | $150 |
Decimal Odds
Decimal odds (common in Europe and Australia) are simpler: they represent total return per unit wagered, including your original stake.
Decimal 2.50 means a $1 bet returns $2.50 total ($1.50 profit + $1 stake).
Converting between formats:
- American to Decimal: If positive: (Odds / 100) + 1. If negative: (100 / |Odds|) + 1
- +150 → (150/100) + 1 = 2.50
- -110 → (100/110) + 1 = 1.909
Implied Probability
This is the most important concept for serious bettors. Implied probability converts odds into a percentage, representing the market's estimated likelihood of that outcome.
Conversion Formulas
From American odds:
- Positive: 100 / (Odds + 100)
- Negative: |Odds| / (|Odds| + 100)
From decimal odds:
- 1 / Decimal Odds
Examples
| American | Decimal | Implied Prob | |----------|---------|-------------| | +200 | 3.00 | 33.3% | | +150 | 2.50 | 40.0% | | -110 | 1.909 | 52.4% | | -150 | 1.667 | 60.0% | | -200 | 1.500 | 66.7% |
The Vig (Juice)
Sportsbooks don't offer fair odds. They build in a margin called the "vig" or "juice." This is how they make money regardless of the outcome.
A standard player prop might be priced at -110 / -110 on Over and Under. Each side implies 52.4% probability, but 52.4% + 52.4% = 104.8%, not 100%.
That extra 4.8% is the vig. To find "true" implied probability, you need to remove the vig:
No-vig probability = Side implied prob / Sum of all implied probs
For -110 / -110: Each side's no-vig probability is 52.4 / 104.8 = 50.0%, a fair coin flip.
Why This Matters for Player Props
When you see a player prop at -110 / -110, the market is saying it's roughly 50/50. But if your model gives the Over a 58% chance, the implied probability (52.4%) is significantly lower than your estimate.
That gap (58% vs 52.4%) represents positive expected value. Over hundreds of bets, consistently finding these gaps is how informed bettors gain an edge.
Comparing Odds Across Books
Different sportsbooks often price the same prop differently. One book might have Over 24.5 at -115 while another has it at -105. The -105 price implies 51.2% vs 53.5%, a meaningful difference.
Line shopping (comparing odds across books) is one of the simplest ways to improve your results. Propboard compares odds across 10 sportsbooks in real time to help you find the best available price.
Putting It All Together
Understanding odds isn't just about knowing what you'll win. It's about understanding what the market believes and where it might be wrong. Every betting decision should start with the question: "Is the true probability higher than the implied probability?"
Try Propboard free to see calibrated probabilities compared against real-time odds from 10 sportsbooks.
Related Reading
- What Is Expected Value? for how to use implied probability to find profitable bets
- Why Line Shopping Matters for how small odds differences compound over hundreds of bets
Frequently Asked Questions
What do negative odds mean?
Negative odds (like -110) tell you how much you need to bet to win $100. At -110, you'd risk $110 to profit $100. The larger the negative number, the heavier the favorite.
What do positive odds mean?
Positive odds (like +150) tell you how much you'd profit on a $100 bet. At +150, a $100 bet profits $150. Positive odds indicate an underdog.
What is the vig (juice)?
The vig is the sportsbook's built-in margin. On a standard -110/-110 line, both sides imply 52.4%, but 52.4% + 52.4% = 104.8%. That extra 4.8% is the vig, which is how sportsbooks guarantee profit regardless of the outcome.
Why does implied probability matter?
Implied probability tells you what the market believes about an outcome. If your model estimates a higher probability than the odds imply, you've found a positive expected value bet. This gap is where informed bettors gain their edge.
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