Betting odds communicate two things: the implied probability of an outcome, and how much you'll be paid if you're right. Understanding both — in any format — is the first step to betting smarter.
American Odds (Moneyline)
American odds are the standard format in US sportsbooks. They're expressed as positive or negative numbers.
Negative odds (favorites): The number tells you how much you need to bet to win $100.
- -150 means bet $150 to win $100 (plus your $150 back)
- -300 means bet $300 to win $100
- The implied probability of -150: 150 / (150 + 100) = 60%
Positive odds (underdogs): The number tells you how much you win on a $100 bet.
- +200 means a $100 bet wins $200
- +130 means a $100 bet wins $130
- The implied probability of +200: 100 / (200 + 100) = 33.3%
Decimal Odds
Popular in Europe, Canada, and Australia. The decimal represents total payout per $1 wagered (including your stake).
- 2.00 = even money (you double your money)
- 1.50 = -200 in American odds
- 3.00 = +200 in American odds
Implied probability from decimal odds: 1 / decimal odds
- 2.50 → 1 / 2.50 = 40% implied probability
Fractional Odds
Common in the UK, especially for horse racing. Expressed as profit-to-stake ratios.
- 3/1 (read "three to one") = win $3 for every $1 wagered = +300 American
- 1/2 = win $1 for every $2 wagered = -200 American
- Evens (1/1) = even money = +100 American
Converting Between Formats
American to decimal (favorite): 1 + (100 / |American|) → -200 becomes 1 + 0.5 = 1.5 American to decimal (underdog): 1 + (American / 100) → +150 becomes 1 + 1.5 = 2.5
Why Implied Probability Matters
The sum of implied probabilities across all outcomes in a market is always greater than 100% — that excess is the vig. A -110/-110 market has:
- 52.38% + 52.38% = 104.76% total implied probability
- The 4.76% excess is the book's margin
Understanding implied probability lets you calculate whether a bet has positive expected value — the key question in every betting decision.
[See implied probabilities and fair odds on every bet with Oddible →]
