Betting Odds Converter
Convert betting odds instantly between American, Decimal, and Fractional formats, and calculate implied probability. Essential for bettors comparing lines across multiple sportsbooks.
About this calculator
Betting odds represent the same probability in different formats depending on the sportsbook or region. American odds (moneyline) use +/- values: positive odds show profit per $100 staked, negative odds show amount needed to win $100. Decimal odds include the stake return, so Decimal = (American / 100) + 1 for positive lines. Fractional odds express profit relative to stake, e.g. 5/2 means $5 profit per $2 staked. Implied probability converts any format to a percentage: for positive American odds, P = 100 / ((odds / 100) + 1); for decimal, P = (1 / odds) × 100. Understanding these conversions lets you quickly identify value by comparing the bookmaker's implied probability against your own estimate.
How to use
Suppose you see American odds of +200 and want the decimal equivalent and implied probability. Step 1: Enter 200 in Odds Value, select 'American' as Input Format. Step 2: Select 'Decimal' as Convert To — result: (200 / 100) + 1 = 3.00. Step 3: Switch Convert To 'Probability' — result: 100 / ((200 / 100) + 1) = 100 / 3 ≈ 33.3%. Step 4: Enter a $50 stake to see profit: 50 × (200 / 100) = $100 profit.
Frequently asked questions
How do I convert American odds to decimal odds for sports betting?
For positive American odds, divide the odds by 100 and add 1. For example, +150 becomes (150 / 100) + 1 = 2.50 in decimal format. For negative American odds, divide 100 by the absolute value of the odds and add 1. So -200 becomes (100 / 200) + 1 = 1.50. Decimal odds always include your original stake in the return, making them easier to use for quick payout calculations.
What does implied probability mean in betting odds?
Implied probability is the win likelihood that the bookmaker's odds suggest, expressed as a percentage. For decimal odds of 2.50, the implied probability is (1 / 2.50) × 100 = 40%. If you believe the true probability is higher than 40%, the bet has positive expected value. Bookmakers inflate implied probabilities beyond 100% collectively — this margin is called the overround or vig, and it guarantees them profit regardless of outcome.
When should I use fractional odds versus decimal odds when comparing bets?
Fractional odds (e.g. 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 calculating exact returns since return = stake × decimal odds. For arbitrage and expected value calculations, decimals are preferred because the formulas are cleaner. Use this converter whenever you're comparing lines from bookmakers in different regions.