Free tool
Odds Converter
Enter odds in any format (decimal, American, or fractional) and see the other two plus the implied probability update instantly.
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How the conversions work
Decimal → American: if decimal ≥ 2, American = (decimal − 1) × 100. If decimal < 2, American = −100 ÷ (decimal − 1). The ± sign flips at exactly 2.00 decimal (evens), which is the break-even point between "risking more than you win" and "winning more than you risk."
Decimal → Fractional: subtract 1 from the decimal odds to get the profit-per-stake ratio, then express it as a fraction (this tool finds the simplest reasonably-sized fraction that matches, since exact fractions can get unwieldy otherwise). 1.95 decimal → 0.95 profit per unit → 19/20.
Implied probability: 1 ÷ decimal odds, regardless of which format you entered. See the fullwalkthroughfor why this always sums to slightly over 100% across both sides of a market, and what to do about it.
Decimal (used across Europe/Australia): total payout per unit staked, including your stake: 1.95 means a €10 bet returns €19.50.American / moneyline: a negative number is how much you must stake to win 100 (e.g. -105); a positive number is how much you win on a 100 stake (e.g. +150).Fractional (traditional in the UK): profit relative to stake: 19/20 means you profit 19 for every 20 staked.
Want to turn that implied probability into an actual edge and stake size? Try the Kelly & Value Calculator.
Worked example: 2.50 and 1.40
- Decimal 2.50 is fractional 3/2 (you win 3 for every 2 staked) and American +150 (you win 150 on a 100 stake).
- Its implied probability is 1 ÷ 2.50 = 40 %.
- Decimal 1.40 is fractional 2/5 and American −250 (you stake 250 to win 100), implied probability 71.43 %.
- Rule of thumb: American odds are positive above decimal 2.00 and negative below it.
Common mistakes
- Reading American −250 as "worse odds" than +150 without converting: they describe a favourite and an underdog, not two prices for the same thing.
- Forgetting that decimal odds include the stake and fractional odds do not (2.50 decimal = 1.50 profit per unit).
- Treating implied probability as the true chance. It still contains the margin; strip it with the no-vig calculator.
In tennis
Most tennis data and exchanges use decimal odds, UK books often show fractions and US books American lines. Converting everything to decimal first makes it easy to compare a price across books, which is the cheapest edge there is.
Read next: No-vig calculator · Tennis betting odds for beginners · Glossary
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