How to Read Sports Betting Odds
Every sportsbook prices its bets in odds. US books default to American odds; international books use decimal or fractional. All three say the same thing in different notation.
American Odds
The format you'll see at every Wisconsin sportsbook. Two flavors:
- Negative number (the favorite): how much you must risk to win $100.
-150= risk $150 to win $100. - Positive number (the underdog): how much you win on a $100 bet.
+200= win $200 on a $100 bet.
+100 (or "even money") means $100 wins $100. Anything between -100 and +100 doesn't exist; books skip that range.
Quick Payout Examples
| Bet | Odds | Payout if Win |
|---|---|---|
| $100 | -110 | $190.91 (profit $90.91) |
| $100 | -200 | $150 (profit $50) |
| $100 | +100 | $200 (profit $100) |
| $100 | +150 | $250 (profit $150) |
| $100 | +300 | $400 (profit $300) |
Decimal Odds
The default in Europe, Canada, Australia. Decimal odds show your total return per $1 staked, including your stake.
1.91= $1 bet returns $1.91 ($0.91 profit + $1 stake). Equivalent to American -110.2.00= $1 returns $2. Equivalent to +100.3.00= $1 returns $3. Equivalent to +200.
To convert American → decimal: positive odds: (odds / 100) + 1. Negative odds: (100 / |odds|) + 1.
Fractional Odds
Standard in the UK and horse racing globally. Shows profit relative to stake.
10/11= stake 11, profit 10. Equivalent to -110 American.1/1("evens") = +100 American.2/1= stake 1, profit 2. Equivalent to +200 American.5/2= stake 2, profit 5. Equivalent to +250 American.
Conversion Table
| American | Decimal | Fractional | Implied Probability |
|---|---|---|---|
| -500 | 1.20 | 1/5 | 83.3% |
| -200 | 1.50 | 1/2 | 66.7% |
| -150 | 1.67 | 2/3 | 60.0% |
| -110 | 1.91 | 10/11 | 52.4% |
| +100 | 2.00 | 1/1 | 50.0% |
| +150 | 2.50 | 3/2 | 40.0% |
| +200 | 3.00 | 2/1 | 33.3% |
| +300 | 4.00 | 3/1 | 25.0% |
| +500 | 6.00 | 5/1 | 16.7% |
Implied Probability
Every odds line implies a probability. It's the math foundation of finding value.
- Negative odds:
|odds| / (|odds| + 100). Example: -150 → 150/250 = 60%. - Positive odds:
100 / (odds + 100). Example: +150 → 100/250 = 40%.
If you think a team's true win probability is higher than the implied number, you've got +EV. That's the entire premise of profitable betting.
Why Both Sides Sum to Over 100%
Both sides of a -110 market imply 52.4% probability. Add them: 104.8%. That extra 4.8% is the book's juice; its structural margin. Sharper books offer -105 (51.2% each side, 102.4% total) which is meaningfully better for high-volume bettors.
Where to Practice
Pull up any current line on a Packers, Bucks, or Brewers game and walk through the math: convert to decimal, compute implied probability, and estimate your edge. After a dozen, the conversions become reflex.