How Odds Work
Odds are the language of sports betting. Learn to read American, fractional, and decimal formats — and calculate exactly what any line is telling you.
What Odds Actually Mean
Odds serve two purposes: they tell you how much you stand to win, and they encode the sportsbook's implied probability that an outcome will occur. Every format — American, fractional, or decimal — expresses the same underlying information in a different way.
The key insight is that odds are not neutral. Sportsbooks build in a margin (called the vig or juice) so that the implied probabilities across both sides of a bet add up to more than 100%. Understanding this is the first step to betting strategically.
The Three Formats
American Odds
The default format in North American sportsbooks. Expressed as a positive or negative number relative to $100.
Bet $100 to win $150 profit. Implied probability: 40%.
Bet $165 to win $100 profit. Implied probability: 62.3%.
Fractional Odds
Common in the UK and Ireland. Written as a fraction — the left number is profit, the right is stake.
Bet $2 to win $3 profit ($5 returned). Implied probability: 40%.
Bet $9 to win $4 profit ($13 returned). Implied probability: 69.2%.
Decimal Odds
Standard in Europe, Australia, and Canada. Represents total return per $1 staked — including your original stake.
Bet $100 to receive $250 total ($150 profit). Implied probability: 40%.
Bet $100 to receive $161 total ($61 profit). Implied probability: 62.1%.
Quick Conversion Reference
The same implied probability expressed in all three formats.
| American | Fractional | Decimal | Implied % |
|---|---|---|---|
| +100 | 1/1 | 2.00 | 50% |
| +150 | 3/2 | 2.50 | 40% |
| -110 | 10/11 | 1.91 | 52.4% |
| -150 | 2/3 | 1.67 | 60% |
| +200 | 2/1 | 3.00 | 33.3% |
| -200 | 1/2 | 1.50 | 66.7% |
The Vig: How Sportsbooks Make Money
On a standard -110 / -110 line (like a point spread), both sides carry an implied probability of 52.4%. Add them together and you get 104.8% — 4.8% over 100%. That excess is the vig, the sportsbook's built-in margin.
To break even against -110 juice, you need to win 52.38% of your bets. Most recreational bettors don't know this number. Strategic bettors do — and they shop for lines to reduce the vig they're paying.
Payout Calculator
Enter your stake and odds to see your potential payout.