Every sports bet starts with the odds. If you don’t understand what -110 or +200 means, you can’t evaluate whether a bet is worth taking. This guide breaks down exactly how American odds work — the math behind the numbers and what they’re really telling you.
What the Numbers Mean
American odds use a base of $100. Every number tells you either how much you need to bet to win $100 (negative odds) or how much you’d win on a $100 bet (positive odds).
Negative Odds (Favorites)
Negative odds tell you how much you bet to win $100 in profit.
| Odds | You Bet | You Win | Total Returned |
|---|---|---|---|
| -110 | $110 | $100 | $210 |
| -150 | $150 | $100 | $250 |
| -200 | $200 | $100 | $300 |
| -300 | $300 | $100 | $400 |
| -500 | $500 | $100 | $600 |
At -110 (the most common odds for spreads and totals), you risk $110 to profit $100. If you win, you get back $210 total — your $110 stake plus $100 profit.
Positive Odds (Underdogs)
Positive odds tell you how much you’d profit on a $100 bet.
| Odds | You Bet | You Win | Total Returned |
|---|---|---|---|
| +100 | $100 | $100 | $200 |
| +150 | $100 | $150 | $250 |
| +200 | $100 | $200 | $300 |
| +300 | $100 | $300 | $400 |
| +500 | $100 | $500 | $600 |
At +200, a $100 bet returns $300 total — your $100 stake plus $200 profit.
The Payout Formula
You don’t have to bet exactly $100. For any bet size:
Negative odds: Profit = Bet Amount / (Odds / 100)
$50 bet at -110: Profit = $50 / 1.10 = $45.45
Positive odds: Profit = Bet Amount × (Odds / 100)
$50 bet at +200: Profit = $50 × 2.00 = $100.00
Implied Probability
Every set of odds implies a probability — what the market thinks the chances are of that outcome happening.
Negative odds: Implied probability = |Odds| / (|Odds| + 100)
-150: 150 / (150 + 100) = 150 / 250 = 60%
Positive odds: Implied probability = 100 / (Odds + 100)
+200: 100 / (200 + 100) = 100 / 300 = 33.3%
| Odds | Implied Probability |
|---|---|
| -500 | 83.3% |
| -300 | 75.0% |
| -200 | 66.7% |
| -150 | 60.0% |
| -110 | 52.4% |
| +100 | 50.0% |
| +150 | 40.0% |
| +200 | 33.3% |
| +300 | 25.0% |
| +500 | 16.7% |
Important: these implied probabilities include the sportsbook’s vig. The true probability is slightly lower than what the odds imply. That’s how the book makes money.
Try the implied-probability-calculator→
Why Both Sides Add Up to More Than 100%
Take a typical spread market:
Team A: -110 (implied 52.4%)
Team B: -110 (implied 52.4%)
Total: 104.8%
That extra 4.8% above 100% is the sportsbook’s vig. In a fair market, both sides would be +100 (50% each, totaling 100%). The vig creates an overround — the implied probabilities add up to more than 100%, guaranteeing the book a margin.
The lower the total overround, the better the odds are for you. A market at -105/-105 (102.4% total) is significantly better than -115/-115 (106.9% total).
Reading Odds in Practice
Spread with Odds
Chiefs -3.5 (-110)
This means: The Chiefs are favored by 3.5 points. If you bet on them, they need to win by 4+ for you to cash. The -110 means you bet $110 to win $100.
Moneyline
Bills +180
The Bills are an underdog. A $100 bet on them to win pays $180 in profit ($280 total returned).
Totals
Over 48.5 (-105)
You’re betting the total combined score will be 49 or more. The -105 means you bet $105 to win $100 — slightly better than the standard -110.
Player Props
Jalen Brunson Over 24.5 Points (-115)
You’re betting Brunson scores 25 or more points. At -115, you bet $115 to win $100. The -115 (instead of -110) means slightly more vig is built into this market.
When Odds Change
Odds aren’t static. They move from the time they’re posted (the “opening line”) until the game starts (the “closing line”). Odds move because of:
Betting volume — money coming in on one side pushes the odds to balance the book’s risk
Sharp action — professional bettors taking a position causes books to adjust
News — injuries, weather, lineup changes all impact the odds
Time — as game time approaches, more information is available and the line becomes sharper
The closing line is generally considered the most accurate set of odds because it incorporates all available information and all betting activity.
Comparing Odds Across Books
Different sportsbooks offer different odds on the same bet. This is normal — each book has its own models, its own customer base, and its own risk position.
| Sportsbook | Bills Moneyline |
|---|---|
| DraftKings | +175 |
| FanDuel | +180 |
| BetMGM | +170 |
| Caesars | +185 |
On a $100 bet, the difference between +170 (BetMGM) and +185 (Caesars) is $15 in potential profit for the exact same outcome. Comparing odds across books before every bet is one of the easiest ways to improve your results over time.
Key Takeaways
Negative odds tell you how much to bet to win $100; positive odds tell you what you’d win on a $100 bet
Every set of odds implies a probability — -110 implies 52.4%, +200 implies 33.3%
Both sides of a market add up to more than 100% because of the sportsbook’s vig
Odds move based on betting action, sharp money, and news
Always compare odds across sportsbooks — price differences on the same bet are free money
