How Betting Odds Work
Betting odds tell you two things at once: how much a winning bet pays, and how likely the sportsbook thinks that outcome is. In the United States you'll mostly see American odds — numbers like -110, +150 or -220 next to every NFL spread, NBA moneyline and MLB total. A minus number is the favorite; it shows how much you must stake to win $100. A plus number is the underdog; it shows how much you win on a $100 stake. Below we work through the exact math, convert those prices to implied probability, and show why two sportsbooks can post the same game at different numbers.
Reading American Odds: Plus and Minus
Every US line uses $100 as its reference point.
- A negative price (e.g. -150) is the favorite. -150 means you risk $150 to win $100 profit. Stake $150, get $250 back total.
- A positive price (e.g. +130) is the underdog. +130 means a $100 stake wins $130 profit. Stake $100, get $230 back total.
The closer a number sits to +100 / -100, the closer the matchup is to a coin flip in the book's eyes. A Chiefs moneyline at -350 signals a heavy favorite; a +280 underdog on the other side signals the book expects them to lose most of the time.
Standard point-spread and totals pricing is usually -110 on both sides. That -110 isn't the true 50/50 price — it's the built-in margin, which we break down further down.
Turning Odds Into a Payout
You don't have to bet in round hundreds. Scale the math to any stake.
For a favorite at -150, divide 100 by the odds number and multiply by your stake: - Profit = stake × (100 / 150) - A $60 bet: 60 × (100 / 150) = $40 profit, $100 total return.
For an underdog at +130, divide the odds by 100 and multiply by your stake: - Profit = stake × (130 / 100) - A $60 bet: 60 × (130 / 100) = $78 profit, $138 total return.
Worked parlay example. Say you build a two-leg NBA parlay: Celtics -140 and Nuggets +120, $50 stake. Convert each leg to decimal first (see next section): -140 = 1.714, +120 = 2.20. Multiply the two decimals: 1.714 × 2.20 = 3.771. Multiply by stake: 50 × 3.771 = $188.57 total return, or $138.57 profit. Every added leg multiplies the payout — and multiplies the ways you can lose.
Odds Converter
American, Decimal and Fractional — Same Price, Different Format
Odds formats are just different clothing on the same number. Most US apps let you switch in settings.
- American +150 = Decimal 2.50 = Fractional 3/2
- American -150 = Decimal 1.667 = Fractional 2/3
- American -110 = Decimal 1.909 = Fractional 10/11
Quick conversions: - Positive American to decimal: (odds / 100) + 1. So +150 → 2.50. - Negative American to decimal: (100 / odds) + 1. So -150 → 1.667.
Decimal is the easiest for parlays because you just multiply the legs together, as in the example above. If you follow European soccer — Serie A, Ligue 1, the Champions League — you'll see decimal odds by default on many international feeds, so it's worth knowing both.
Implied Probability: What the Odds Actually Predict
Every price converts to an implied probability — the chance the outcome must have for the bet to break even long term.
- Negative odds: probability = odds / (odds + 100). So -150 → 150 / 250 = 60%.
- Positive odds: probability = 100 / (odds + 100). So +130 → 100 / 230 = 43.5%.
This is the single most useful skill in betting. If you think the Nuggets win closer to 50% of the time but the book prices them at +130 (43.5% implied), the price is in your favor. If your own read is below the implied number, the bet has no edge no matter how much you like the team.
For a standard -110 both ways, each side implies 52.4%. Two sides adding to 104.8% instead of 100% is the tell that the book has baked in its margin.
The Vig: Why Both Sides Aren't Priced Fairly
The extra 4.8% in a -110/-110 market is the vig (also called juice or margin). It's how sportsbooks make money regardless of who wins. Remove it and you get the book's true estimate.
Across the games we sample, average margins differ meaningfully by operator: - FanDuel: ~4.5% average margin (594 markets sampled) - DraftKings: ~4.3% average margin (1,066 markets sampled) - Fanatics Sportsbook: ~4.2% average margin (466 markets sampled) - Caesars Sportsbook: ~5.3% average margin (904 markets sampled) - BetMGM: ~5.2% average margin (436 markets sampled) - BetRivers: ~6.4% average margin (478 markets sampled)
Lower margin means the price is closer to true odds, so more of a winning bet stays in your pocket. A -108 line pays more than a -115 line on the same outcome. Over a season of hundreds of bets, that gap compounds. This is why line shopping across books matters more than any single promo.
These figures reflect sampled market pricing, not a claim about any single game today — always check the live number before you bet.
Best-Price Share: Who Posts the Sharpest Number
Margin tells you the average markup; best-price share tells you how often a book actually posts the top number when you compare the same market side by side.
From our sampled markets: - DraftKings tops the price on about 54% of sampled markets - Fanatics Sportsbook: ~42% - Caesars Sportsbook: ~36% - FanDuel: ~36% - BetRivers: ~28% - BetMGM: ~19%
No book wins every market, which is the whole point of comparing. A number that's best on an NFL spread may lag on an MLB run line or a UFC moneyline. Our odds pages and comparison tools let you line up the same fixture across operators before you commit. On editorial ratings for odds quality, bet365 scores 8.8 and DraftKings 7.9 — the highest two in this group — which broadly tracks the pricing data above.
How Odds Move Before Kickoff
Opening odds aren't final. They shift as money comes in and as news breaks — a starting QB ruled out, an NBA load-management scratch, an MLB pitcher change, weather at an outdoor NFL game.
When a lot of money hits one side, the book shortens that price and lengthens the other to balance its liability. That's a market move, and it often reflects new information. If you took Nuggets +120 in the morning and the number drifts to +105 by tip-off, your earlier price is now better than what's on the board. Tracking these shifts on our market movers page helps you time your bet — sometimes the smart play is to wait, sometimes it's to grab a number before it gets worse.
Live odds work the same way but faster, updating point by point during the game. Cash Out values are derived from those live prices, letting you settle a bet early at the current implied probability rather than waiting for the final whistle.
Odds and Legal Betting in Your State
US sports betting is regulated state by state. An operator licensed in New Jersey by the DGE is not automatically legal in New York, Pennsylvania, Michigan or anywhere else — availability, the minimum age (21 in regulated markets) and even which markets are offered depend on your state regulator.
That matters for odds because not every book operates in every state, so the set of prices you can actually compare depends on where you are. In a mature market with all nine operators live, you have more shots at the best number than in a state with only two or three books. Check our legal betting sites hub for what's available where you are before you start comparing lines.
FAQ
What does -110 mean in betting?
-110 means you risk $110 to win $100 profit. It's the standard price on both sides of a point spread or total. Each -110 side carries an implied probability of 52.4%, and the extra 4.8% above a fair 50/50 is the sportsbook's margin, or vig.
What's the difference between +150 and -150?
+150 is an underdog: a $100 stake wins $150 profit ($250 total return). -150 is a favorite: you must stake $150 to win $100 profit ($250 total return). The plus side is always the less likely outcome and pays more per dollar risked.
How do I convert American odds to probability?
For negative odds, divide the number by itself plus 100: -150 → 150/250 = 60%. For positive odds, divide 100 by the number plus 100: +150 → 100/250 = 40%. That percentage is the implied chance the book assigns to the outcome.
Why do sportsbooks have different odds on the same game?
Each book sets its own margin and reacts to betting money differently. In our sampled markets, average margins range from about 4.2% (Fanatics) to 6.4% (BetRivers), and DraftKings posts the top price on roughly 54% of markets. Comparing books before you bet gets you the sharper number.
Is decimal or American odds better?
Neither is more accurate — they express the same price. Decimal odds are simpler for parlays because you multiply the legs together, while American odds are the default across US sportsbooks. Most apps let you switch formats in settings.
What is the vig and how does it affect my payout?
The vig (or juice) is the sportsbook's built-in margin, visible when a market's two sides add up to more than 100% implied probability. A lower-margin price like -108 returns more than -115 on the same bet, so shopping for the lowest vig increases your long-run payout.