How the Odds Converter Works
The Betstamp Odds Converter instantly converts odds between American, Decimal, and Fractional formats. Enter odds in any one format and the calculator returns the equivalents in the other two plus the implied probability.
How to Use the Odds Converter
- Enter odds in any one format:
- Fractional Odds (e.g., 3/2)
- Decimal Odds (e.g., 2.50)
- American Odds (e.g., +150)
- The calculator updates the other two formats automatically
- It also outputs Implied Probability (the break-even win rate at those odds)
Decimal to American Odds Conversion
Decimal odds are standard across Europe, Canada, Australia, and most of the world outside the US. American odds are standard in the United States.
Decimal to American:
- Decimal ≥ 2.00: American = (Decimal – 1) × 100 (e.g., 2.50 → +150)
- Decimal < 2.00: American = –100 / (Decimal – 1) (e.g., 1.50 → –200)
Common conversions: | Decimal | American | Fractional | Implied Probability | |---|---|---|---| | 1.50 | –200 | 1/2 | 66.7% | | 1.91 | –110 | 10/11 | 52.4% | | 2.00 | +100 | 1/1 | 50.0% | | 2.50 | +150 | 3/2 | 40.0% | | 3.00 | +200 | 2/1 | 33.3% | | 4.00 | +300 | 3/1 | 25.0% | | 6.00 | +500 | 5/1 | 16.7% | | 11.00 | +1000 | 10/1 | 9.1% |
American to Decimal Odds Conversion
American to Decimal:
- Positive American odds: Decimal = (American / 100) + 1 (e.g., +150 → 2.50)
- Negative American odds: Decimal = (100 / |American|) + 1 (e.g., –200 → 1.50)
Decimal is easier to work with mathematically. You multiply decimal odds to build parlays (see the [Betstamp Parlay Calculator]) and can flip to implied probability with 1/Decimal.
Fractional Odds
Fractional odds are common in the UK and Ireland and express profit relative to stake. 5/1 means you win $5 profit for every $1 staked. 1/2 means you win $1 profit for every $2 staked. Fractional odds are visually clean but less efficient for parlay and probability math.
Fractional to Decimal: (Numerator / Denominator) + 1. So 5/1 → 6.0, and 1/2 → 1.5.
Implied Probability Explained
Every set of odds implies a probability — the win rate a bet would need to hit to break even.
Implied probability formulas:
- From decimal: 1 / Decimal
- From American positive: 100 / (American + 100)
- From American negative: |American| / (|American| + 100)
Break-even win rates at common odds:
- +300 → 25% (need to win 1 in 4)
- +200 → 33.3% (1 in 3)
- +100 → 50%
- –110 → 52.4% (standard NFL/NBA spread juice)
- –200 → 66.7% (2 in 3)
- –500 → 83.3%
Understanding implied probability is step one toward +EV betting. Compare implied probability to your own estimated true probability (or use the [Betstamp No-Vig Fair Odds Calculator] to devig a sharp-book line) — if your number is higher, it's a +EV bet.
Why Odds Format Matters for Bettors
Decimal is the standard format for sharp math. Parlays multiply cleanly, probability is 1/decimal, and international comparisons are easier. Most serious bettors default to decimal regardless of location.
American odds are still the norm in US sportsbooks, so US bettors need to be fluent in converting. Fractional is mostly a display preference in UK markets.
With Betstamp PRO—the most advanced top-down betting odds screen in the market. Bettors will find hundreds of daily betting edges with ease, allowing you to scale your profits long-term. Click the banner to book a free demo.
