Convert between American (moneyline), decimal, and fractional odds instantly. Enter a value in any format and see all conversions plus implied probability in real time.
Single Odds Converter
Enter odds in any format — all other formats update instantly.
Multi-Outcome Overround Calculator
Enter odds for each outcome to see total implied probability and the bookmaker's margin (vig).
Understanding Odds Formats
| Format | Example | How It Works | Common Where |
|---|---|---|---|
| American (Moneyline) | +150 / -200 | Positive: profit on $100 bet. Negative: amount to bet to win $100 | U.S. sportsbooks |
| Decimal | 2.50 | Total return per $1 bet (includes stake) | Europe, Australia |
| Fractional | 3/2 | Profit per unit staked (3 profit for every 2 staked) | UK, Ireland |
| Implied Probability | 40% | The probability the odds imply for the outcome | Universal (internal) |
Conversion Formulas
American to Implied Probability:
def american_to_implied(odds):
if odds > 0:
return 100 / (odds + 100)
else:
return abs(odds) / (abs(odds) + 100)
# Examples:
# +150 → 100 / 250 = 0.40 (40%)
# -200 → 200 / 300 = 0.667 (66.7%)
Decimal to Implied Probability:
def decimal_to_implied(odds):
return 1 / odds
# Example: 2.50 → 1 / 2.50 = 0.40 (40%)
Fractional to Implied Probability:
def fractional_to_implied(numerator, denominator):
return denominator / (numerator + denominator)
# Example: 3/2 → 2 / 5 = 0.40 (40%)
What Is Overround (Vig)?
The overround is the bookmaker’s built-in margin. In a fair market, the implied probabilities for all outcomes should sum to exactly 100%. When they sum to more than 100%, the excess is the bookmaker’s edge.
For example, in a two-outcome market where Book A offers -110 on both sides:
- Implied probability for each side: 52.38%
- Total: 104.76%
- Overround: 4.76% — this is the vig the bookmaker collects
When the total implied probability sums to less than 100% across different bookmakers, that’s an arbitrage opportunity. Use the Arbitrage Calculator to find optimal stakes for exploiting these gaps.
Related Resources
- Arbitrage Calculator — Calculate arb percentages and optimal stakes
- Sports Betting Arbitrage Bot Guide — Complete technical guide to building arb bots
- Cross-Market Arbitrage Guide — Arbing between prediction markets and sportsbooks
- Cross-Market Arb Finder — Find arb opportunities across Polymarket, Kalshi, and sportsbooks
For live odds across 10+ sportsbooks in a single API, see TheOddsPulse.