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.
Common Odds Reference Table
| American | Decimal | Fractional | Implied Prob | Payout per $100 |
|---|---|---|---|---|
| -500 | 1.200 | 1/5 | 83.33% | $120.00 |
| -300 | 1.333 | 1/3 | 75.00% | $133.33 |
| -200 | 1.500 | 1/2 | 66.67% | $150.00 |
| -150 | 1.667 | 2/3 | 60.00% | $166.67 |
| -130 | 1.769 | 10/13 | 56.52% | $176.92 |
| -110 | 1.909 | 10/11 | 52.38% | $190.91 |
| +100 | 2.000 | 1/1 | 50.00% | $200.00 |
| +110 | 2.100 | 11/10 | 47.62% | $210.00 |
| +150 | 2.500 | 3/2 | 40.00% | $250.00 |
| +200 | 3.000 | 2/1 | 33.33% | $300.00 |
| +300 | 4.000 | 3/1 | 25.00% | $400.00 |
| +500 | 6.000 | 5/1 | 16.67% | $600.00 |
| +1000 | 11.000 | 10/1 | 9.09% | $1,100.00 |
Betting Odds Glossary
Overround — The bookmaker’s margin, expressed as the amount by which total implied probabilities for all outcomes in a market exceed 100%. A market with 104.76% total implied probability has a 4.76% overround.
Vig (Vigorish) — Short for vigorish, the commission a bookmaker charges on each bet. Synonymous with juice and overround. In the U.S., the standard vig is -110 on both sides, giving the book a 4.76% edge.
Juice — Slang for the bookmaker’s commission on a wager, used interchangeably with vig and vigorish. A market with more juice has a higher bookmaker margin.
Hold Percentage — The percentage of total money wagered that the sportsbook expects to keep as profit over time. Related to but distinct from vig: hold is calculated on total handle, while vig is built into the odds of a single market.
True Odds (No-Vig Odds) — The odds that would exist if the bookmaker’s margin were removed entirely. Calculated by dividing each outcome’s implied probability by the total, then converting back to odds.
Implied Probability — The probability of an outcome as suggested by the betting odds, before removing the bookmaker’s margin. American odds of -200 imply a 66.7% probability; +150 implies 40%.
Even Money — Odds that pay exactly 1-to-1: +100 American, 2.00 decimal, or 1/1 fractional. A winning even-money bet doubles your stake. Also called pick’em when applied to point-spread markets.
Chalk (Favorite) — The outcome with the lowest payout and highest implied probability. A heavy chalk is a strong favorite, typically at -200 or shorter.
Underdog (Dog) — The outcome with the higher payout and lower implied probability. Shown as positive American odds, decimal odds above 2.00, or fractional odds where the numerator exceeds the denominator.
Moneyline — A bet on which side will win outright, with no point spread. Moneyline odds are expressed in American format: negative for favorites, positive for underdogs.
Edge — The percentage advantage a bettor has over the bookmaker’s implied probability. If your model says 55% but the book implies 50%, your edge is 5 percentage points.
Expected Value (EV) — The average profit or loss per bet over the long run. Positive EV (+EV) bets are profitable long-term; negative EV (-EV) bets favor the book.
Closing Line — The final odds offered just before a market closes. Beating the closing line consistently is the strongest indicator of a skilled bettor.
Line Movement — A change in odds over time, driven by betting volume, sharp action, or new information. Odds moving from -150 to -170 indicate increased market confidence in that outcome.
For a complete guide to sportsbook terminology, see Sportsbook Terminology Guide.
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 The Odds API.