American Odds

American odds (also called moneyline odds) are the +/- format used by most US sportsbooks. They look like +150 or -200, and the number tells you how the bet sizes around a $100 base.

The two cases

Negative odds (favorites): the number is how much you’d risk to win $100.

• -110 → risk $110 to win $100 (or $11 to win $10)
• -200 → risk $200 to win $100 ($2 risked per $1 won)
• -500 → risk $500 to win $100 (heavy favorite)

Positive odds (underdogs): the number is how much you’d win on a $100 stake.

• +150 → bet $100 to win $150 (total payout $250)
• +300 → bet $100 to win $300 (total payout $400)
• +1000 → bet $100 to win $1,000 (longshot)

The bigger the absolute number on a favorite, the heavier the favorite. The bigger the positive number on an underdog, the longer the longshot.

Converting to decimal odds

Decimal odds are easier to do math on (especially for parlays). To convert:

• Positive American: decimal = (american / 100) + 1. So +150 → 2.50.
• Negative American: decimal = (100 / |american|) + 1. So -110 → 1.91.

Implied probability shortcut

• Negative odds: probability = |odds| / (|odds| + 100). So -110 → 110/210 = 52.4%.
• Positive odds: probability = 100 / (odds + 100). So +150 → 100/250 = 40.0%.

Why books use this format in the US

Tradition mostly. American sportsbooks have used moneyline odds since horse racing established them. Decimal odds are more common everywhere else (UK, Europe, Australia). Most US books now let you toggle between formats in the app, but the default is still American.