American Odds: A Complete Guide

You walk into a sportsbook app, look at a game, and see prices like -110, +150, or -1500. The numbers feel arbitrary. They aren’t — they encode probability, payout, and the book’s margin in a single compact value, and once you can read them fluently you can size up any line in your head.

This guide walks through American odds end-to-end: how to read them, what they imply about probability, how to convert them to decimal or fractional odds when the math gets clunky, and the common mistakes retail bettors make when they treat the dollar number as a feeling instead of a math problem.

Why American odds exist

American odds (also called moneyline odds) are the format US sportsbooks default to. Their structure goes back to horse racing — bookmakers needed a way to quote prices around a $100 base, and the +/- format does that compactly.

The rest of the world uses decimal odds (1.91 instead of -110) or fractional odds (10/11 instead of -110). Decimal is the easiest format to do math on and is what every parlay calculator on earth converts to internally. American odds win on compactness — you can fit a hundred lines on a screen — and on tradition.

Most modern US apps let you toggle between formats. Even if you stay in American mode for daily use, learn to convert: the math is faster in decimal.

Negative odds: what -110 means

Negative American odds describe favorites — sides the book thinks are more than 50/50 to win. The number tells you how much you’d risk to win $100.

• -110 — risk $110 to win $100. The standard “vig” coin-flip price. Bet $11 to win $10. Bet $110 to win $100.
• -150 — risk $150 to win $100.
• -200 — risk $200 to win $100. The book thinks this side wins about 67% of the time.
• -500 — heavy favorite. Risk $500 to win $100. Implied probability ~83%.
• -1500 — heavy chalk. Risk $1,500 to win $100. Implied probability ~94%.

The bigger the absolute number on a favorite, the heavier the favorite — and the worse the dollar payout for picking the obvious winner.

Positive odds: what +150 means

Positive American odds describe underdogs — sides priced under 50%. The number tells you how much you’d win on a $100 stake.

• +100 — even money. $100 wins $100.
• +150 — bet $100 to win $150 in profit (total payout $250). Implied probability 40%.
• +300 — bet $100 to win $300. Implied 25%.
• +500 — bet $100 to win $500. Implied ~17%.
• +1500 — bet $100 to win $1,500. Implied ~6%. A real longshot.

Positive odds are where casual bettors over-bet. The dollar payout looks tantalizing — bet $100 to win $1,500 — but the implied probability (6%) is the only number that should drive the decision. You’ll lose 14 of 15 attempts on average.

The vig hidden in -110

Both sides of a coin-flip line are typically priced at -110, not at +100 / -100. That asymmetry is the vig — the book’s margin built into every line.

Implied probability of -110: 52.4%.

Both sides at 52.4% adds up to 104.8%, not 100%. The 4.8% gap is the vig. The book wins it on the average bet over time, regardless of which side cashes individual games.

This is why the “natural” win rate to break even on a -110 spread bet isn’t 50% — it’s 52.4%. Beat that across hundreds of bets and you’re +EV. Hit exactly 50% and you slow-bleed.

For a deeper dive, see the Vig glossary entry. The takeaway: the vig is the reason most retail bettors lose long-term. You’re not just predicting outcomes; you’re predicting outcomes well enough to clear the book’s margin.

Converting American to decimal

Decimal odds are easier to math on, especially for parlays. Two cases:

Positive American → decimal:

decimal = (american / 100) + 1

So +150 → (150/100) + 1 = 2.50.

Negative American → decimal:

decimal = (100 / |american|) + 1

So -110 → (100/110) + 1 = 1.91.

A few common conversions worth memorizing:

American	Decimal	Implied prob
-110	1.91	52.4%
-150	1.67	60.0%
-200	1.50	66.7%
+100	2.00	50.0%
+150	2.50	40.0%
+200	3.00	33.3%
+500	6.00	16.7%

The Implied Probability Calculator does this conversion in either direction for any odds you type in.

Implied probability — the only number that matters

The price is always the probability the book is implying. Implied probability strips the dollars off and gives you a clean percentage to compare against your own estimate.

Negative American shortcut:

probability = |odds| / (|odds| + 100)

So -110 → 110/210 = 52.4%.

Positive American shortcut:

probability = 100 / (odds + 100)

So +150 → 100/250 = 40.0%.

The whole game of finding edges is comparing your true probability estimate to the implied probability. If you think a +150 underdog actually wins 45% of the time (vs the book’s 40%), you have edge. The Kelly Criterion calculator sizes the bet based on that edge.

Parlays multiply decimal odds, not American

This is where most casual bettors trip. American odds don’t multiply. To math out a parlay, every leg has to be converted to decimal first.

Three legs at -110 each:

1.91 × 1.91 × 1.91 ≈ 6.97

That’s the combined decimal. Convert it back to American: (6.97 − 1) × 100 ≈ +597. So a 3-leg -110 parlay pays roughly +597, not “negative something” and not the sum of the legs.

If you’ve ever been confused why parlay calculators ask you to type in odds and spit out a different number, this is why. They’re converting to decimal in the background and multiplying.

For the full math and the trap of stacking parlays anyway, see Parlays Explained.

Common American-odds mistakes

1. Reading -200 as “twice as likely as +100” -200 implies 66.7%, not 50% × 2 = 100%. The relationship between American odds magnitude and probability is non-linear.

2. Stacking favorite parlays because each leg “looks like a lock” Three -200 favorites parlay at 1.50³ ≈ 3.38 (≈ +238 American), but the implied probability is 0.667³ ≈ 30% — the parlay loses 70% of the time.

3. Comparing dollar-payouts across different stakes “I won $300 on a +300 bet, that’s better than a +200 win” — only if you bet the same amount. Always compare in units of stake, not dollars.

4. Ignoring the vig when comparing books Book A posts -108/-112. Book B posts -110/-110. Same juice? No — Book A has lower vig on the favorite side. Sharp bettors line-shop precisely because these small gaps add up over thousands of bets.

5. Thinking +EV = certain win EV is long-run average. Even +5% EV bets lose individual flips routinely. Don’t size up after a few wins thinking you’ve “figured it out.”

Bottom line

• Negative odds = risk N to win 100. Favorites.
• Positive odds = bet 100 to win N. Underdogs.
• Implied probability is what matters, not the dollar number.
• -110 has 4.8% vig built in. Beat 52.4% to win net.
• Parlays multiply decimal odds, not American. Always convert first.
• Compare your probability to the book’s implied probability. That gap is your edge (or your hole).

If you came here for the calculator and stayed for the math, browse the rest of the tools or skim the glossary. The site is built around helping you read prices well enough that the dollar number stops driving the decision.