Why odds formats matter for crypto sportsbooks
Different odds formats show the same underlying price in different ways. Learning to read and convert them helps you compare lines across books, spot better value, and avoid mistakes when a site defaults to a format you don’t usually use. Education pages from major bookmakers and exchanges stress that odds are just expressions of probability, no matter the display.
Decimal odds explained
Decimal odds show the total return per unit staked, including your stake. If you bet 1 unit at 2.50 and win, your return is 2.50; your profit is 1.50. This “return-including-stake” convention is why decimals are popular across Europe and on many exchanges and crypto sportsbooks. Smarkets’ help center defines decimal odds this way and shows simple return math: odds × stake = total return.
Fractional odds explained
Fractional odds, common in the UK and Ireland and especially in horse racing, quote potential profit relative to stake. At 3/2, a 2-unit stake returns 5 units in total: 3 units profit plus your 2-unit stake back. Leading operator help pages and converters describe fractional odds in these terms.
American (moneyline) odds explained
American odds use a plus/minus system around 100. Positive numbers tell you how much profit you’d make from a 100-unit stake; negative numbers tell you how much you must stake to profit 100 units. For example, +150 means 150 profit on 100 staked; −200 means stake 200 to profit 100. This is the standard used on U.S. books. Guides from trusted outlets lay this out clearly.
Converting between formats
Use these core conversions:
- American → Decimal
For positive odds: Decimal = 1 + (American/100). For negative odds: Decimal = 1 − (100/American). Example: +150 → 2.50; −200 → 1.50. AceOdds lists the full set of conversion formulas and a live converter. - Fractional → Decimal
Decimal = (numerator/denominator) + 1. Example: 3/2 → 2.50. This rule is consistent across reputable calculators and guides. - Fractional ↔ American
Positive American = 100 × (numerator/denominator). Negative American = −100 ÷ (numerator/denominator). Example: 10/11 ↔ −110; 7/4 ↔ +175. See the operator and calculator references.
Implied probability formulas (all three formats)
Implied probability is the probability embedded in the price. Knowing it lets you compare the book’s view against your own model or intuition.
- Decimal odds D: p = 1/D. Example: 1.50 implies 66.67%; 3.50 implies 28.57%.
- Fractional odds n/d: p = d / (n + d). Example: 3/2 implies 40%.
- American odds A:
For positive A: p = 100 / (A + 100). For negative A: p = |A| / (|A| + 100). Example: +200 implies 33.33%; −150 implies 60%. Multiple education pages show the same formulas.
Tip: if all three formats confuse you, a reputable converter shows the equivalent decimal, fractional, American and the implied probability side by side.
Checking “fairness” with a quick margin/overround test
Margins (also called overround, vig, or hold) tell you how much cushion a sportsbook has baked into a market. Lower is generally better for you.
- Two-way example: −110/−110 in American equals about 52.38% + 52.38% = 104.76%. The margin is 4.76%.
- Decimal example: 1.95/1.95 implies 1/1.95 + 1/1.95 ≈ 102.56%, so the margin is 2.56%.
Exchange guides explain how to compute margin: convert each selection to implied probability, add them up, then subtract 100%. Education pieces and calculators from Smarkets and Matchbook demonstrate this and why coin-toss markets should be 100% in theory. Wikipedia’s “Mathematics of bookmaking” page shows how margins compound in parlays/accumulators.
If you want a tool to do the addition, use an overround calculator and input every outcome’s price.
Regional habits and how to change formats in your account
Decimal is common in Europe and on many crypto-first books; fractional is still used in parts of the UK and Ireland; American dominates in the United States. Many operators let you switch formats in settings, and some crypto sportsbooks publish tutorials covering all three. Operator help pages confirm the display options and give examples of equivalent prices such as 10/11 = −110 = 1.91.
FAQs
Which format is best for beginners?
Decimal is often easiest because it shows total return per unit and turns implied probability into a one-step calculation (1 divided by the odds). This is why exchanges and many global books prefer it.
Why do crypto sportsbooks often default to decimal?
Crypto-facing sites serve international audiences and exchanges, where decimal is a common standard. Guides from major crypto sportsbooks cover all three formats, but their examples and UI often default to decimal.
How do I compare lines across books quickly?
Convert each price to implied probability, add margin checks for the market, and then pick the book with the lower margin and better side. You can also use a converter to see American, decimal, and fractional equivalents at a glance.
Do odds equal true probabilities?
No. Odds include margin; they also incorporate a book’s risk management. Regulator guidance for virtual events even states displayed odds should reflect probabilities as closely as possible, but margins and market forces still play a role.
Quick reference: conversions and examples
| Original | Convert to | Result | Notes |
|---|---|---|---|
| +150 (American) | Decimal | 2.50 | 1 + (150/100) |
| −200 (American) | Decimal | 1.50 | 1 − (100/−200) |
| 3/2 (Fractional) | Decimal | 2.50 | (3/2) + 1 |
| 7/4 (Fractional) | American | +175 | 100 × 7/4 |
| 1.91 (Decimal) | American | −110 | 100 ÷ (1.91 − 1) with sign applied |
| 2.75 (Decimal) | Fractional | 7/4 | 2.75 − 1 = 1.75 = 7/4 |
Reference formulas and equivalences are documented by specialist calculators and operator guides.
