Betting Odds Converter
Converts between American, decimal, and fractional betting odds and computes implied probability and potential winnings. Essential for bettors comparing lines across multiple sportsbooks or shopping international markets.
Last updated: May 2026
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About this calculator
Betting odds express the same probability in different formats depending on the sportsbook or region. American odds (moneyline) use ± values: positive odds show profit per $100 staked (+150 = $150 profit on $100), negative odds show stake required to win $100 (−200 = $200 to win $100). Decimal odds include the stake return: payout = stake × decimal_odds, so 2.50 decimal returns $2.50 per $1 staked. Fractional odds (UK style) express profit as a fraction of stake (5/2 means $5 profit per $2 staked). Conversion formulas: American(+) → decimal = (odds/100) + 1; American(−) → decimal = (100/|odds|) + 1; decimal → American(≥2) = (decimal − 1) × 100; decimal → American(<2) = −100 / (decimal − 1); decimal → fractional = decimal − 1 (then express as a fraction); fractional → decimal = (numerator/denominator) + 1. Implied probability = 1/decimal_odds for any format after conversion. Variables: oddsValue (the numeric value), inputFormat (american/decimal/fractional), outputFormat (target format), stake (optional, for payout calculation). Edge cases: even money is +100 American = 2.00 decimal = 1/1 fractional = 50% implied. American odds discontinuously switch sign at decimal 2.00, requiring two separate formulas. Fractional odds with non-integer denominators (like 10/11) are common in UK markets — the calculator handles these as floats. Implied probabilities across all outcomes of an event sum to more than 100% — the excess is the bookmaker's margin (overround/vig), typically 4–8% for major markets.
How to use
Example 1: Convert American +200 to decimal and probability with a $50 stake. Step 1: input 200, format = American. Step 2: decimal = (200/100) + 1 = 3.00. Step 3: probability = 1/3.00 × 100 = 33.3%. Step 4: profit = $50 × (200/100) = $100; total return = $150. Verify: 33.3% implied probability matches even money plus a 2:1 payout, exactly what +200 represents. Example 2: Convert decimal 1.50 to American odds and implied probability. Step 1: input 1.50, format = Decimal. Step 2: since 1.50 < 2, American = −100 / (1.50 − 1) = −100 / 0.50 = −200. Step 3: probability = 1/1.50 × 100 = 66.7%. Verify: at 1.50 decimal, $1 returns $1.50 (50¢ profit on $1 risked), equivalent to $200 risked to win $100 (American −200) — confirmed.
Frequently asked questions
How do I convert American odds to decimal odds for sports betting?
For positive American odds, divide by 100 and add 1: +150 becomes (150/100) + 1 = 2.50 decimal. For negative American odds, divide 100 by the absolute value and add 1: −200 becomes (100/200) + 1 = 1.50 decimal. Decimal odds always include your original stake in the return, making them easier for quick payout calculation — multiply stake × decimal to get total payout. Decimal is the standard in Europe, Australia, and on betting exchanges, while American is standard at U.S. sportsbooks. Converting all lines to a single format makes shopping across multiple books much faster and reduces arithmetic errors.
What does implied probability mean in betting odds?
Implied probability is the win likelihood the bookmaker's odds suggest, expressed as a percentage. For decimal odds, implied probability = (1 / decimal) × 100. For decimal 2.50, that is 40%. If your model estimates the true probability is higher than 40%, the bet has positive expected value. Bookmakers inflate implied probabilities so that the sum across all outcomes exceeds 100% — the excess is called the overround, vig, or juice, and it guarantees the book a long-run profit regardless of which side wins. Typical NFL spreads have ~4% overround per side (total ~108%), while obscure markets can run 15%+ overround.
When should I use fractional odds versus decimal odds?
Fractional odds (5/1, 7/2) are traditional in UK horse racing and show only profit relative to stake, making quick mental math straightforward for round fractions. Decimal odds are standard in Europe, Australia, and on betting exchanges, and are mathematically simpler for exact returns because total return = stake × decimal_odds. For arbitrage and expected-value calculations, decimal is preferred because the formulas are cleaner. Use this converter whenever you're comparing lines from bookmakers in different regions or formats — Asian handicap markets typically use decimal, US bookmakers use American, and UK racing prefers fractional. Some pros use Hong Kong odds (similar to decimal but without the stake) for compactness.
What are common mistakes when converting betting odds?
Confusing American +200 with American −200 — one is a favorite, one is an underdog, and they imply very different probabilities (33% vs 67%). Forgetting that decimal odds include the stake (decimal 2.00 = even money, not 'double your money on top of your stake'). Mistaking fractional 5/4 for the number 1.25 — it actually represents 1.25 + 1 = 2.25 decimal. Ignoring overround when summing implied probabilities — for two-outcome markets, true probability of each side = implied / (sum of implied for all sides), normalizing the overround out. Treating extreme American odds (+5000) as exotic when they simply represent 1.96% implied probability — same math, just very small odds. Forgetting to compare lines after conversion gives an artificial preference to the format you're most familiar with.
When should I NOT rely solely on odds conversion?
Conversion alone does not tell you whether a bet has value — you still need an independent probability estimate to compare against the implied probability. For exchange betting on Betfair or Smarkets, the published odds already exclude commission, so converting them doesn't account for the 2–5% commission deducted on net winnings. Live in-play odds change so quickly that any conversion is stale within seconds — use real-time line monitoring tools instead. Asian handicap markets with partial spreads (e.g., −0.25, −0.75) have split-stake payouts that simple conversion doesn't capture; the result depends on the actual margin of victory. Promotional offers (boosted odds, parlay insurance, profit boosts) add asymmetric value that pure conversion ignores. Finally, for arbitrage and dutching strategies, use specialized arb and dutching calculators instead of comparing converted lines manually.