Betting odds tell you two things: the probability of an outcome and how much you will win relative to your stake. For matched betting, decimal odds are what matter most — they are used by betting exchanges and most UK bookmakers.
Decimal odds (the most important for matched betting)
Decimal odds show your total return per £1 staked — including your original stake. They are the standard format on UK betting exchanges.
- Odds of 2.0 = double your money (£10 stake returns £20 total = £10 profit)
- Odds of 3.0 = triple your money (£10 stake returns £30 total = £20 profit)
- Odds of 1.5 = £10 stake returns £15 total = £5 profit
- Formula: Profit = (Odds − 1) × Stake
Fractional odds (traditional UK format)
Fractional odds show profit relative to stake. They are still common on UK bookmaker websites and in horse racing.
- 2/1 (two-to-one) = £10 stake wins £20 profit
- 1/2 (one-to-two) = £10 stake wins £5 profit
- Evens (1/1) = £10 stake wins £10 profit
- To convert to decimal: divide the fraction and add 1. 2/1 = 2 + 1 = 3.0
American odds (moneyline)
American odds use + and − signs. They are less common in the UK but you may encounter them on US sports or some international bookmakers.
- +200 = £100 wins £200 profit (equivalent to decimal 3.0)
- −150 = you must bet £150 to win £100 profit
- Positive odds: profit per £100 staked
- Negative odds: how much you must stake to win £100
Implied probability
Odds also represent the bookmaker's implied probability of an event. Decimal odds of 2.0 imply a 50% chance (1 ÷ 2.0 = 0.5). Odds of 4.0 imply a 25% chance. The bookmaker builds a margin ("overround") into the odds, which is why the implied probabilities for all outcomes in a market add up to more than 100%.
Why matched betting uses close back/lay odds
When your back odds (at the bookmaker) and lay odds (at the exchange) are close together, the qualifying loss is minimised. The matched betting calculator uses both odds to calculate the optimal lay stake and expected qualifying loss.
See how back and lay odds affect your profit with the free calculator.
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