The standard odds format in Europe and on exchanges, expressing total return per unit staked — including the return of the stake itself.
Decimal odds represent the total amount returned per £1 staked — including the original stake. A £10 bet at 3.50 returns £35 (£25 profit + £10 stake). This makes profit calculation straightforward: total return = stake × decimal odds; profit = stake × (decimal odds − 1).
Decimal odds are the default format on all major betting exchanges (Betfair, Smarkets) and most European bookmakers. They replaced fractional odds as the standard format in the UK and Ireland during the 2000s due to their simplicity and ease of comparison.
To convert decimal to implied probability: divide 1 by the decimal odds. 2.50 → 1 ÷ 2.50 = 40%. To convert from fractional: decimal = (numerator ÷ denominator) + 1. So 3/2 = 1.50 + 1 = 2.50. To convert from American positive odds: decimal = (American odds ÷ 100) + 1. +150 → 1.5 + 1 = 2.50.
Implied Probability
The probability of an outcome embedded in bookmaker odds — calculated by dividing 1 by the decimal odds.
Fractional Odds
The traditional UK odds format, expressing profit relative to stake as a fraction — 3/1 means £3 profit for every £1 staked.
American Odds (Moneyline)
The US betting format: positive odds show profit on a £100 stake; negative odds show the stake required to profit £100.
Value Bet
A bet where the odds offered by the bookmaker are higher than the true probability of the outcome, giving you a positive expected value over the long run.
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