KEY TAKEAWAYS
American odds are the three-digit numbers with a plus or minus sign that U.S. sportsbooks use to price a bet — for example, -150 or +130. The sign tells you which side is favored: a minus sign marks the favorite, and a plus sign marks the underdog. The number itself tells you exactly how much you would win, or need to risk, relative to a $100 stake.
Reading American odds correctly means being able to do three things: identify the favorite and the underdog from the sign alone, convert the number into an implied probability — the market’s built-in estimate of how likely that outcome is — and calculate the actual profit and payout on any stake size. This matters because the price a sportsbook posts is not just a label. It is the mechanism that decides what a winning bet actually returns, and how much confidence the market has priced into that outcome.
This article walks through what the plus/minus format means, the exact formulas for converting odds into probability and payout, a full worked example, and the mistakes bettors most often make when reading these numbers.
What American Odds Actually Represent
American odds — also called moneyline odds — express a price as a number tied to a $100 baseline stake, with the sign showing which side the market favors. A negative number, such as -150, is read as “how much you must stake to profit $100.” A positive number, such as +130, is read as “how much you would profit on a $100 stake.” The sign is a label for favorite or underdog, not a judgment about whether a price is good or bad.
The favorite always carries negative odds because a bettor is risking more to win less — the market considers that outcome more likely, so the price reflects lower risk on paper. The underdog always carries positive odds because a smaller stake can win a larger profit, compensating for the higher chance the bet loses. This relationship is fixed: a true favorite cannot carry positive American odds, and a true underdog cannot carry negative American odds. If a matchup ever appears to show the reverse, the favorite/underdog labeling — not the math — is what’s wrong.
Every American odds number a sportsbook posts already has the vig — the book’s built-in margin — baked into it. That means the number is not a neutral statement of chance; it is a price that already includes the house’s edge. Understanding that distinction is what separates reading odds correctly from just reading them literally.
How to Convert Odds to Probability and Payout
Two things happen the moment a sportsbook posts an American odds number: it implies a probability, and it defines a payout. Both follow fixed formulas, and which version applies depends only on the sign — these are the same two questions every bettor eventually asks: what does this price imply about the chance of winning, and, as it’s often phrased, if I bet $100, how much do I win?
Implied Probability
For a favorite (negative odds), implied probability equals the odds’ absolute value divided by that absolute value plus 100. For an underdog (positive odds), it equals 100 divided by the odds plus 100. Implied probability is also the break-even probability — the win rate a bettor would need at that exact price just to come out even, before accounting for the vig.
Profit and Payout
For a favorite, profit equals the stake multiplied by 100 divided by the odds’ absolute value. For an underdog, profit equals the stake multiplied by the odds divided by 100. In both cases, payout equals the stake plus that profit. Payout always includes the original stake back; profit is only the amount won on top of it.
| Scenario | Implied Probability | Profit on a $100 Stake | Payout on a $100 Stake |
|---|---|---|---|
| Favorite, e.g. -150 | 150 ÷ (150 + 100) = 60% | 100 × (100 ÷ 150) = $66.67 | $100 + $66.67 = $166.67 |
| Underdog, e.g. +130 | 100 ÷ (130 + 100) ≈ 43.48% | 100 × (130 ÷ 100) = $130.00 | $100 + $130.00 = $230.00 |
Notice that the favorite’s 60% and the underdog’s 43.48% add up to 103.48%, not 100%. That extra 3.48% is the vig — the sportsbook builds its margin directly into both prices, so the two implied probabilities in a two-way market will almost always sum to slightly more than 100%.
A Worked Example: Reading a Real Matchup
Suppose a sportsbook lists a hypothetical matchup as Team A at -150 and Team B at +130. Team A is the favorite: implied probability is 150 ÷ (150 + 100) = 60%. A $100 stake on Team A profits $66.67 (100 × 100 ÷ 150), for a total payout of $166.67 if Team A wins. Team B is the underdog: implied probability is 100 ÷ (130 + 100) ≈ 43.48%. A $100 stake on Team B profits $130 (100 × 130 ÷ 100), for a payout of $230 if Team B wins.
Adding both implied probabilities gives 60% + 43.48% = 103.48%, confirming the vig is built into this hypothetical market. No matter which side wins, the total amount a sportsbook collects from losing bettors on that side of the market slightly exceeds what it pays out to winners on the other. These odds are a hypothetical example used only to illustrate the math — not a specific, current sportsbook line.
Common Mistakes When Reading American Odds
The most frequent error is treating payout and profit as the same number — payout is profit plus the original stake, so a $230 payout on a $100 underdog bet is not $230 of winnings. Another common mistake is assuming a -150 favorite is a near-certain winner; a 60% implied probability still means that side loses a meaningful share of the time, before even accounting for the vig. Bettors also sometimes forget that the sign only marks favorite versus underdog, not whether a price is competitive — a -110 line and a -130 line are both favorites, just at different costs. Finally, some readers convert the odds correctly but then forget the vig is already baked in, treating implied probability as a neutral, fair estimate rather than a price that includes the house’s edge.
How This Shows Up at the Sportsbook
On a real bet slip, American odds appear next to every selection, and reading them correctly is the first skill a bettor uses before placing anything. Confirming which side carries the minus sign shows which team the market favors, at a glance, before looking at anything else. Converting the number to implied probability lets a bettor gauge how much confidence the market has priced into an outcome — a reference point, not a prediction of what will actually happen. Calculating profit and payout before confirming a bet is how a bettor knows exactly what a stake returns if it wins, which matters more as odds move away from a simple -110/-110 baseline.
This interpretation skill carries over immediately into other markets. Point spreads, totals, and player props are usually still priced in American odds format, so the same probability and payout formulas apply regardless of what the wager is actually on. Sportsbooks also adjust these numbers frequently as betting activity and information change, so the specific price on a bet slip today is not guaranteed to hold an hour from now. Reading the format itself, however, never changes — the formulas stay identical no matter which sportsbook, sport, or moment a bettor is looking at.
Reading American odds is the foundation for two related skills covered elsewhere on this blog: converting between odds formats (American, decimal, and fractional), and understanding how vig affects the true value of a price across an entire market. Once the plus/minus format and its formulas feel automatic, the natural next step is learning how sportsbooks build that margin into a market, and how bettors evaluate whether a given price actually represents fair value.
