How to Read Odds: 3 Formats, 1 Skill That Changes Everything
How to read odds in 3 formats with 7 worked examples. American, decimal, and fractional odds explained so you never misread a line again.
A -110 line costs you $110 to win $100. A +300 line pays $300 on a $100 stake. Decimal 2.50 means your total return is 2.5x your bet. These are three ways of saying the same thing: price. Learning how to read odds is the single most important skill in sports betting, prediction markets, and event contracts. Every calculation you will ever run (expected value, Kelly sizing, vig extraction) starts with reading the number in front of you correctly.
This guide breaks down three odds formats with worked examples, conversion formulas, and the implied probability math hiding behind every line. If you want the full conversion toolkit, the odds converter guide covers every formula. This article focuses on reading and interpreting what the numbers actually mean.
How to Read American Odds
American odds are the default format on US sportsbooks like DraftKings and FanDuel. They revolve around $100.
Negative odds (-150): The amount you must risk to win $100 profit. Positive odds (+200): The amount you win on a $100 risk.
The minus sign means favorite. The plus sign means underdog. The number tells you the price.
Worked example: -150 favorite
You bet $150 to win $100. If the bet wins, you get back $250 total ($150 stake + $100 profit). Your profit margin on the risk is 66.7%.
Worked example: +200 underdog
You bet $100 to win $200. If the bet wins, you get back $300 total ($100 stake + $200 profit). Your profit margin on the risk is 200%.
The -110 standard
Most point spreads and totals are priced at -110 on both sides. This means you risk $110 to win $100. The extra $10 is the vig (also called juice), which is the sportsbook's built-in fee. At -110/-110, the total vig is about 4.5%. The hold calculator quantifies this for any two-sided market, and the article on what vig actually costs you breaks down why it matters more than most bettors realize.
| American Odds | Stake to Win $100 | Profit on $100 Stake | Implied Probability |
|---|---|---|---|
| -300 | $300 | $33.33 | 75.0% |
| -200 | $200 | $50.00 | 66.7% |
| -150 | $150 | $66.67 | 60.0% |
| -110 | $110 | $90.91 | 52.4% |
| +100 | $100 | $100.00 | 50.0% |
| +150 | $100 | $150.00 | 40.0% |
| +200 | $100 | $200.00 | 33.3% |
| +300 | $100 | $300.00 | 25.0% |
The pattern: as the negative number gets bigger, the favorite gets heavier and the implied probability climbs. As the positive number gets bigger, the underdog gets longer and the implied probability drops.
How to Read Decimal Odds
Decimal odds are the standard in Europe, Australia, and on most prediction market platforms. They represent the total return per $1 wagered, including your stake.
Formula: Total Return = Stake x Decimal Odds
Decimal odds of 2.50 mean a $10 bet returns $25 ($15 profit + $10 stake). Decimal odds of 1.50 mean a $10 bet returns $15 ($5 profit + $10 stake).
The key difference from American: decimal odds always include the stake in the number. Decimal 2.00 is a coin flip (even money). Anything below 2.00 is a favorite. Anything above 2.00 is an underdog.
Worked example: decimal 1.91
This is the decimal equivalent of -110. Bet $100, get back $191. Profit: $91.
Most US bettors see -110 and think "I know what that means." Then they visit Polymarket or a European exchange and freeze at 1.91. It is the same price. The odds converter translates between formats instantly, but understanding the logic means you never need to pause.
Worked example: decimal 3.00
This is +200 in American. Bet $50, get back $150. Profit: $100.
Decimal odds shine in parlay math. To calculate a parlay payout in decimal, just multiply the legs together. A 3-leg parlay at 1.91 x 2.50 x 3.00 = 14.325 total return per dollar. Try doing that in American odds and you will understand why sharp bettors think in decimal.
| Decimal Odds | American Equivalent | Implied Probability | $100 Bet Returns |
|---|---|---|---|
| 1.25 | -400 | 80.0% | $125 |
| 1.50 | -200 | 66.7% | $150 |
| 1.91 | -110 | 52.4% | $191 |
| 2.00 | +100 | 50.0% | $200 |
| 2.50 | +150 | 40.0% | $250 |
| 3.00 | +200 | 33.3% | $300 |
| 5.00 | +400 | 20.0% | $500 |
How to Read Fractional Odds
Fractional odds are the traditional format in the UK and Ireland. Written as 5/1 ("five to one"), they show profit relative to stake.
Formula: Profit = Stake x (Numerator / Denominator)
At 5/1, a $10 bet wins $50 profit. Total return: $60. At 1/5, a $50 bet wins $10 profit. Total return: $60.
The number on the left is your potential profit. The number on the right is your stake. When the left number is bigger (5/1), it is an underdog. When the right number is bigger (1/5), it is a favorite.
Common fractional odds and their equivalents
| Fractional | Decimal | American | Implied Probability |
|---|---|---|---|
| 1/1 (evens) | 2.00 | +100 | 50.0% |
| 2/1 | 3.00 | +200 | 33.3% |
| 5/1 | 6.00 | +500 | 16.7% |
| 1/2 | 1.50 | -200 | 66.7% |
| 1/5 | 1.20 | -500 | 83.3% |
| 10/11 | 1.91 | -110 | 52.4% |
You will encounter fractional odds on UK sportsbooks and in horse racing. For everything else, convert to decimal. The conversion is simple: Decimal = (Numerator / Denominator) + 1. So 5/1 becomes (5/1) + 1 = 6.00. The full conversion reference lives in odds formats explained.
From Odds to Implied Probability: Where the Real Math Starts
Reading odds is step one. The step that actually matters is converting those odds into implied probability, because probability is the language of edge.
The three conversion formulas
American (negative): Implied Probability = |Odds| / (|Odds| + 100) American (positive): Implied Probability = 100 / (Odds + 100) Decimal: Implied Probability = 1 / Decimal Odds Fractional: Implied Probability = Denominator / (Numerator + Denominator)
Worked example: is this bet +EV?
A sportsbook prices the underdog at +180. You estimate the true win probability at 40%.
Step 1: Convert +180 to implied probability. 100 / (180 + 100) = 100 / 280 = 35.7%.
Step 2: Compare. Your estimate (40%) is higher than the implied probability (35.7%). The gap is 4.3 percentage points.
Step 3: This is a +EV bet. The sportsbook is underpricing the underdog relative to your model. Run the exact numbers through the EV calculator to quantify the expected profit, then use the Kelly Criterion calculator to determine optimal bet size. The Kelly Criterion guide explains the full framework.
This three-step process (read, convert, compare) is the core loop of sports betting math. Every professional bettor runs it on every single bet.
Odds on Prediction Markets and Event Contracts
Prediction markets like Kalshi and Polymarket display prices differently from sportsbooks. A contract priced at $0.65 means the market implies a 65% probability. A contract at $0.35 implies 35%. The prices are the implied probabilities.
This makes prediction markets the easiest format to read. A "Yes" contract at $0.72 on Kalshi means you pay $0.72 to win $1.00 if the event happens. Your profit is $0.28 on a $0.72 risk. In American odds, that is roughly -257. In decimal, 1.389.
The catch: prediction markets still have vig. If "Yes" is $0.72 and "No" is $0.32, the total is $1.04. That extra $0.04 is the market's built-in cost. Use the de-vig calculator to strip it and find the true implied probabilities. The article on closing line value explains why tracking these true probabilities over time is the best predictor of long-term profit.
Robinhood event contracts use the same cent-based pricing. The format is intuitive once you recognize that the contract price IS the implied probability expressed as a dollar amount.
Mistakes Beginners Make When Reading Odds
Confusing stake and profit in American odds. At -150, you risk $150 to profit $100. Your total return is $250, not $150. The negative number is your cost, not your payout.
Ignoring the vig. Two sides at -110 each imply a combined 104.8% probability. That is mathematically impossible. The extra 4.8% is the sportsbook's cut. Always de-vig before estimating true probability.
Thinking bigger negative numbers are better bets. A -500 favorite has an 83.3% implied probability. If the true probability is only 78%, that is a -EV bet despite being a heavy favorite. Price matters more than probability.
Not converting before comparing. You cannot compare -150 on DraftKings to $0.58 on Kalshi without converting both to the same scale. Pick one format (decimal or implied probability) and standardize everything.
Frequently asked questions
- What does -110 mean in betting?
- A -110 line means you risk $110 to win $100 profit. It is the standard price for point spreads and totals, and it includes approximately 4.5% vig (the sportsbook's fee). The implied probability is 52.4%.
- How do you convert American odds to probability?
- For negative odds: divide the absolute value by (absolute value + 100). So -200 becomes 200/300 = 66.7%. For positive odds: divide 100 by (odds + 100). So +150 becomes 100/250 = 40%. These are implied probabilities before removing the vig.
- Which odds format is best for calculating payouts?
- Decimal odds. Total return equals stake multiplied by decimal odds. For parlays, multiply the decimal odds of each leg together. American odds require different formulas for positive and negative numbers, making parlay math unnecessarily complex.
- What is the difference between odds and probability?
- Odds express a price you pay or receive on a bet. Probability expresses the likelihood of an outcome as a percentage. Odds include the vig (sportsbook's fee), so implied probability from odds always overstates true probability. Strip the vig with a de-vig calculator to estimate the real number.
- How do prediction market prices relate to betting odds?
- A prediction market contract priced at $0.65 implies a 65% probability, equivalent to -186 American or 1.538 decimal. The contract price is essentially the implied probability expressed as a dollar amount, making prediction markets the most intuitive format for probability-first thinkers.