American odds (also called moneyline odds) are the standard format used in the United States and Canada. Unlike other formats, American odds come in two variants indicated by a plus or minus sign:
- Positive odds (+): Show how much profit you make on a $100 stake. At +300, a $100 bet returns $400 ($300 profit + $100 stake).
- Negative odds (-): Show how much you must stake to profit $100. At -150, you stake $150 to win $100, returning $250 in total.
The plus/minus sign immediately tells you whether a selection is the underdog (positive) or the favourite (negative). When odds are identical on both sides — such as +100/-100 — there is no favourite and no underdog.
Converting to decimal is straightforward with two formulas. For positive odds: (odds/100) + 1. For negative odds: (100/|odds|) + 1. A +250 line becomes 3.50 decimal; a -200 line becomes 1.50 decimal.
The bookmaker margin in American odds is visible through the gap between the positive and negative lines on a two-way market. A typical two-side market might show -110 on both sides. Converting: 100/110 + 1 = 1.909 for both sides. Implied probabilities: 52.4% + 52.4% = 104.8%, confirming a 4.8% margin built in.
American odds are becoming more familiar to international bettors as US sportsbooks expand globally and major US leagues (NBA, NFL, MLB, NHL) attract worldwide betting interest.
Example
Super Bowl: Kansas City Chiefs -140 vs Philadelphia Eagles +120. To win $100 on the Chiefs, you must stake $140 (total return $240). To bet on the Eagles at +120, a $100 stake returns $220 ($120 profit). The Chiefs are the favourite; the Eagles are underdogs.