Understanding Betting Odds: Decimal, Fractional & Implied Probability

Odds tell you two things: how much a bet pays, and the probability the bookmaker assigns to it.

Decimal vs fractional

• Decimal (2.50): your total return per £1 staked, including the stake. £10 at 2.50 returns £25.
• Fractional (3/2): profit relative to stake. 3/2 = 2.50 in decimal.

Implied probability

Convert decimal odds to a percentage: 1 ÷ odds. Odds of 2.0 imply 1 ÷ 2.0 = 50%. Odds of 4.0 imply 25%.

The margin (overround)

Add up the implied probabilities of every outcome and you'll get more than 100% — that extra is the bookmaker's built-in margin. Shopping for the best price shrinks that margin against you.

Finding value

A bet has value when your estimated probability is higher than the odds imply. That's the whole idea behind value betting and our published value-bet track record.

Bet responsibly — stats describe tendencies, not certainties. See our responsible gambling guidance.