How to Read Betting Odds: Formats and Probability
Sportsbooks post betting odds as a price tag on an outcome. Learning how to read betting odds comes down to two quick checks: what the odds imply about win chance, and what they pay if the bet wins.
American odds (like -110 or +150) dominate US menus, yet decimal and fractional formats show up in settings and niche markets.
How Betting Odds Work
Odds show the price attached to an outcome and the payout if that outcome happens. Betting sites post that price in a format bettors can read quickly, most often American odds in the US. The number is doing two jobs at once: it states what the book will pay, and it hints at how likely the result is based on the market price.
That likelihood is the implied probability. As a quick reference, a common line like -110 implies about a 52.38% break-even win rate. That percentage is useful because it lets readers compare prices across different markets without getting stuck on bet types.
Odds can include a sportsbook margin, often called the vig. One sign is that the implied probabilities on both sides of a two-way market add up to more than 100%. That extra percentage is part of how a book prices risk across the board.
Implied probability is a pricing tool, not a prediction, because the posted number includes a margin and can move with market demand.
How to Read Betting Odds (American, Decimal, Fractional)
Reading any line gets simpler with a repeatable routine.
- Identify the format. US books default to American (+/−); some menus let users switch to decimal.
- Read the sign first. A plus number signals an underdog price; a minus number signals a favorite price.
- Translate to “risk to win.” American odds are quoted around a $100 reference point.
- Convert when comparing markets. Decimal or implied probability makes cross-sport comparison easier.
American odds: the plus and minus in betting
In this guide, payout on $100 means winnings; total return means stake plus winnings.
American odds use a plus or minus sign to show how much you win relative to $100, or how much you must risk to win $100.
- +150 means a $100 stake returns $150 in winnings (total return $250).
- -200 means you risk $200 to win $100 (total return $300).
Those examples stay consistent across moneylines, spreads, totals, and props; only the underlying market changes.
Decimal odds: one number that bakes in stake
Decimal odds show the total return per $1 staked, including stake. A common US price like -110 converts to about 1.91 in decimal form. A $100 stake at 1.91 returns about $191 total, meaning about $91 in winnings.
Fractional odds: return relative to stake
Fractional odds show winnings relative to stake. 5/2 means $5 won for every $2 risked. That equals +250 in American terms, since a $100 stake would return $250 in winnings. Fractional pricing turns up most often in horse racing menus and some international feeds, even when USA sportsbooks list American odds by default.
Odds Conversion Table (American, Decimal, Fractional)
| American | Decimal | Fractional | Implied Probability |
|---|---|---|---|
| -110 | 1.91 | 10/11 | 52.38% |
| -150 | 1.67 | 2/3 | 60.00% |
| +100 | 2.00 | 1/1 | 50.00% |
| +120 | 2.20 | 6/5 | 45.45% |
| +200 | 3.00 | 2/1 | 33.33% |
How Do Betting Odds Work as Probability Math
Odds can be translated into implied probability, which is the break-even win rate for that price. This is the cleanest way to compare markets when learning how to read odds across different bet types.
Implied probability from American odds uses two formulas:
- Negative odds (favorite): probability = odds / (odds + 100)
- Positive odds (underdog): probability = 100 / (odds + 100)
A common line like -110 implies 110 / (110 + 100) = 110 / 210 = 0.5238, or about 52.38%. A price of +120 implies 100 / (120 + 100) = 100 / 220 = 0.4545, or about 45.45%.
Vig shows up when a two-way market prices both sides above 100% combined. Example: -115 implies 53.49% and -105 implies 51.22%, totaling 104.71%. That extra 4.71% is the built-in margin, which is why spreads and totals often sit near -110.
How to Read Betting Lines
Super Bowl LIX is the reference point for the examples below. The example prices are representative of common listings near kickoff and are included to keep the payout and probability math consistent across bet types.
Use the same routine across bet types: identify the market, then read the odds as price and implied probability.
- Moneyline: This line focuses only on the winner. Ahead of Super Bowl LIX on February 9, 2025, Kansas City was priced as a modest favorite across many books, with Philadelphia listed as the underdog; the figures shown here (KC around -130 and PHI around +110) are example prices used for payout and probability math.
- Point spread: The spread introduces a scoring adjustment. A common listing had Kansas City at -1.5 (-110), meaning the Chiefs needed to win by at least 2 points for the bet to cash. Ticket math example: $100 at -110 pays $90.91 in winnings (total return $190.91). Break-even win rate is 52.38%.
- Total (over/under): Totals focus on combined points. A common listing near 48.5 (-110) meant bettors were pricing the full-game score, not the teams. The payout math stayed consistent on both sides, even though the outcome target changed.
- Price movement vs line movement: If the spread stayed at -1.5 but the odds shifted from -110 to -120, that change reflected price pressure rather than a new expectation on the score margin. “Opening” is the first widely posted number, while the “closing line” is the last consensus price before the game starts.
- Higher payouts: Longer odds, such as +180 instead of +120, signal lower implied probability. The high payouts come because the outcome is priced as less likely, not because the bet carries special status.
Comparison Table: Common Betting Odds Explained
Viewing odds side by side helps translate price into probability and payout. The comparison below uses Super Bowl LIX market conventions to anchor the math in a real setting.
The lines below are example prices used to demonstrate conversion, implied probability, and payout math in a real-event context. ESPN provides the Super Bowl LIX odds context and recap coverage, and the AGA provides US wagering estimates tied to the game.
| Market Type | Example Line | Odds Format | Implied Probability | Payout on $100 |
|---|---|---|---|---|
| Moneyline favorite | KC -130 | American | 56.52% | $76.92 |
| Moneyline underdog | PHI +110 | American | 47.62% | $110 |
| Point spread | KC -1.5 (-110) | American | 52.38% | $90.91 |
| Total points | O/U 48.5 (-110) | American | 52.38% | $90.91 |
| Futures example | KC SB winner +450 | American | 18.18% | $450 |
Across these markets, the same math applies every time. Odds adjust probability and payout, even when the bet type changes. Once the format is familiar, comparing lines becomes a numbers exercise rather than a guessing exercise.
Understanding Betting Odds: Casino vs Sportsbook
Casino odds and sportsbook odds use similar language, yet they measure different things. Sportsbook odds are a posted price on a specific outcome. That price converts into implied probability and a payout, and it can change before an event starts as money comes in.
Casino odds are tied to game rules and built-in math, not a market that moves. Blackjack is a clean example. Changing a natural blackjack payout from 3:2 to 6:5 typically increases the house edge by about 1.4 percentage points under otherwise similar rules, because the payout rule changes expected return.
Casino pricing is generally stable during play, and the “odds” are better understood as return mechanics. Sportsbook pricing is dynamic, and the “odds” are better understood as a tradable price. That distinction holds across mixed gambling menus, including listings for real money betting sites and online casinos.
Common Slip-ups when Reading Lines
Misreading a number is easy when formats change quickly. These are the mistakes that show up most often when people first work through how do odds work in practice:
- Treating a minus sign as a lower payout rather than a higher implied win rate.
- Confusing total return with winnings, especially in American odds.
- Comparing odds across markets without converting to implied probability.
- Assuming longer odds mean better opportunity rather than lower expectation.
- Mixing decimal and American formats on the same bet slip.
- Ignoring price movement and focusing only on the points or total.
- Reading futures prices as short-term probabilities.
Spotting these issues early keeps the math consistent and avoids costly misreads when lines move close to game time.
Reading Betting Odds Without Second-Guessing
Odds reading gets easier once the numbers mean the same thing across markets.
Start with the format, then translate the sign, then convert to implied probability when lines need a clean comparison. That routine works on moneylines, spreads, totals, and futures, even when pricing shifts close to game time.
A final check helps: confirm that the payout shown on the ticket matches the odds format you intended to use, since many menus let users switch formats without warning.
Need help? Call 1-800-GAMBLER.