American odds, implied probability, payout calculations — everything you need to understand what those numbers actually mean before you bet a dollar.
If you've ever looked at a sportsbook and seen "-110" or "+250" and felt confused about what those numbers mean and how much you'd actually win — this guide is for you. Understanding odds is the single most important foundational skill in sports betting. Everything else builds on this.
American odds (also called moneyline odds) are expressed as positive or negative numbers, typically in increments from -10000 to +10000. Every number you see on a sportsbook in the US is formatted this way.
The logic is simple once you grasp it:
Important: in all cases, your original bet (the stake) is returned to you along with your winnings when you win. So a $100 bet at +150 that wins returns $250 to your account — $100 stake + $150 in profit.
You don't always bet $100. Here's how to calculate profit on any bet size:
Example: You bet $50 at -200.
Profit = $50 × (100/200) = $50 × 0.5 = $25 profit. You get back $75 total ($50 stake + $25 profit).
Example: You bet $50 at +250.
Profit = $50 × (250/100) = $50 × 2.5 = $125 profit. You get back $175 total ($50 stake + $125 profit).
Implied probability is the win percentage a set of odds represents. It's the most important concept for evaluating whether a bet has value — because "value" means the true win probability exceeds the implied probability baked into the price.
Example: -200 odds → 200/(200+100) = 200/300 = 0.667 = 66.7% implied win probability
Example: +150 odds → 100/(150+100) = 100/250 = 0.40 = 40% implied win probability
If you believe a team has a 50% true chance of winning, but the odds are -120 (implying 54.5%), that bet has negative value. If the odds are +110 (implying 47.6%), that same 50% probability bet has positive value. Finding gaps between true probability and implied probability is the entire game.
Notice that on most standard bets, you see -110 on both sides of a spread or total. That means you bet $110 to win $100 on either team. If you did the math on both sides, the implied probabilities add up to more than 100% — typically around 104-110%.
That "extra" percentage is the vig (vigorish), also called juice or the house edge. It's how sportsbooks make money. Standard -110/-110 lines carry about 4.5% vig. That's the hurdle every bettor needs to overcome.
This means to break even betting at standard -110 lines, you need to win 52.38% of your bets. Most amateur bettors don't hit that threshold consistently. Line shopping (finding the best available odds at multiple books) is the simplest way to reduce the vig you're paying.
Different sportsbooks post slightly different odds on the same game. Getting +105 instead of +100 on a bet you're going to make anyway adds up significantly over hundreds of bets. Here's why it matters:
If you make 500 bets per year at an average of +100 instead of +105, and you win 53% of them, the difference in profit is substantial. The extra 5 cents per bet across 500 wagers represents meaningful real money. Serious bettors maintain accounts at 3-4 books and always check odds before placing.
Before placing any bet, check at least 2-3 books. DraftKings, FanDuel, BetMGM, and Caesars often have 5-10 point differences on the same market. Getting -105 instead of -110 on every spread bet saves you real money over a season.
A parlay combines 2+ bets into one. All legs must win for the parlay to cash. The potential payout is calculated by multiplying the decimal equivalents of each leg's odds together.
Converting American to decimal odds: Negative odds → (100/|odds|)+1. Positive odds → (odds/100)+1.
Example: 2-team parlay, both legs at -110.
-110 in decimal = (100/110)+1 = 1.909
Parlay multiplier = 1.909 × 1.909 = 3.65
Bet $100 on this parlay → Win $265 profit ($365 return - $100 stake)
The key thing to understand: books pay out parlays at odds slightly less than "true" parlay math would suggest. The vig compounds with each leg. A 4-leg parlay at standard odds carries roughly double the vig of a single bet. Parlays are fun, but they're higher-vig products. Use them selectively.
Once you internalize odds as implied probabilities, your betting mindset shifts. You stop asking "will this team win?" and start asking "is the book's implied probability lower than my estimate of their true win probability?" That's how professionals think. That's how you find value.
Every bet is ultimately a statement: "I believe this outcome is more likely than the odds suggest." When that belief is backed by real analysis — not gut feel — you have a foundation for long-term profitability.