This converter is an educational tool for understanding different odds formats and implied probability. It does not provide betting advice, tips, or predictions.
Odds Converter
Enter odds in any format — the others update automatically.
Odds formats
Use this odds converter to flip between exchange-friendly decimal odds, traditional fractional prices and
American moneyline quotes. Implied probability updates instantly so you can spot the market expectation at
a glance.
How the conversion works
Fractional → Decimal:Decimal = 1 + (a ÷ b)
American → Decimal:Decimal = 1 + (value ÷ 100) for positive, 1 + (100 ÷ |value|) for negative.
Probability → Decimal:Decimal = 1 ÷ p where p is the implied probability as a decimal.
Different betting markets use different odds formats. UK bookmakers traditionally use fractional odds (e.g. 5/1), betting exchanges like Betfair use decimal odds (e.g. 6.0), and American sportsbooks use moneyline odds (e.g. +500). This converter lets you switch between all three formats instantly and see the implied probability — the percentage chance the odds suggest.
Understanding implied probability is fundamental to exchange trading. If a selection is priced at 4.0 decimal, the implied probability is 25%. If your own analysis suggests the true probability is 30%, there may be value in backing it. Conversely, if you think the probability is only 20%, you might consider laying. The converter makes these comparisons quick and intuitive.
Detailed conversion examples
Here are five common odds expressed in all three formats with their implied probabilities:
Evens: Fractional 1/1 = Decimal 2.0 = American +100 = 50.0% implied probability
Short price: Fractional 1/4 = Decimal 1.25 = American −400 = 80.0% implied probability
Medium price: Fractional 3/1 = Decimal 4.0 = American +300 = 25.0% implied probability
Long shot: Fractional 10/1 = Decimal 11.0 = American +1000 = 9.1% implied probability
Very short: Fractional 1/10 = Decimal 1.1 = American −1000 = 90.9% implied probability
Notice that American odds work differently depending on whether the selection is favourite or outsider. Negative American odds (e.g. −400) show how much you must stake to win £100. Positive American odds (e.g. +300) show how much you win from a £100 stake.
Common mistakes with odds conversion
Confusing fractional and decimal formats: Fractional 5/1 is decimal 6.0, not 5.0. The decimal format includes your returned stake; fractional does not.
Misreading American odds: −150 does not mean you lose £150. It means you need to stake £150 to win £100. The sign indicates favourite (negative) or underdog (positive).
Assuming implied probability = true probability: Implied probability includes the bookmaker's margin. The sum of all implied probabilities in a market typically exceeds 100% — the excess is the overround or "vig."
Rounding errors in manual conversion: Small rounding differences can affect staking calculations. Use a converter rather than mental arithmetic for precise results.
