Win Probability From Odds Calculator
Convert decimal, American (moneyline) or fractional betting odds into the implied win probability they represent.
How it works
Decimal: p = 1 ÷ odds · American +m: p = 100 ÷ (m + 100) · American −m: p = m ÷ (m + 100) · Fractional a/b: p = b ÷ (a + b)
Every odds format encodes an implied probability — the payout the bookmaker is willing to offer. Decimal odds are the total return per unit staked, so their reciprocal is the probability. American odds pivot on 100: positive numbers show profit on a 100 stake, negative numbers show the stake needed to win 100. Because bookmakers build in a margin, the implied probabilities across all outcomes sum to more than 100%.
Worked example
Decimal odds of 2.50 imply p = 1 ÷ 2.50 = 40%. The same bet in American odds is +150 (win 150 on a 100 stake): p = 100 ÷ (150 + 100) = 40%. As fractional odds 3/2: p = 2 ÷ (3 + 2) = 40%. All three describe the identical 40% break-even line.
Sources: Odds — Wikipedia
Frequently asked questions
Why do the odds imply my break-even win rate?
The implied probability is exactly the fraction of bets you must win to neither gain nor lose over time. Beat it consistently and you profit; win less often and the odds grind you down.
Why do a match's probabilities add up to more than 100%?
The excess over 100% is the bookmaker's margin, or "vig" — it is how they guarantee a profit. Removing it (normalising the probabilities to sum to 100%) gives the "fair" odds, which are always a little longer than the posted ones.
How do I convert between the formats?
Convert everything to decimal odds first: decimal = 1 ÷ p. American positive = (decimal − 1) × 100; American negative = −100 ÷ (decimal − 1). Fractional = (decimal − 1) as a fraction. This calculator does all three at once.
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This calculator is for educational purposes. Double-check important results before acting on them.