What is the Fractional Odds Calculator?
Fractional odds are the traditional format used in UK and Irish betting, written as a fraction such as 5/2 ("five to two"). This calculator converts any fractional odds plus your stake into the total payout, your profit, the implied probability, and the equivalent decimal odds. It is a universal betting maths tool, though the fractional format itself is most common in the UK and Ireland (currency shown in £).
How to use it
Enter the numerator (A) and denominator (B) of the odds — for 5/2, A is 5 and B is 2. Enter the amount you want to stake. The calculator returns your total return (stake plus winnings), the profit on its own, the implied win probability, and the decimal-odds equivalent.
The formula explained
Profit equals stake × (A ÷ B). Your total payout adds the stake back: $$\text{Payout} = \text{Stake} \times \frac{A}{B} + \text{Stake}$$ The implied probability is \(B \div (A + B)\), expressed as a percentage. Decimal odds equal \((A \div B) + 1\), so a payout can also be found as Stake × decimal odds.
Worked example
For odds of 5/2 with a £10 stake: profit = 10 × (5 ÷ 2) = £25. Total payout = 25 + 10 = £35. Implied probability = 2 ÷ (5 + 2) = 0.2857 ≈ 28.57%. Decimal odds = (5 ÷ 2) + 1 = 3.5.
$$\text{profit} = 10 \times \left(\frac{5}{2}\right) = £25$$ $$\text{Total payout} = 25 + 10 = £35$$ $$\text{Implied probability} = \frac{2}{5 + 2} = 0.2857 \approx 28.57\%$$ $$\text{Decimal odds} = \left(\frac{5}{2}\right) + 1 = 3.5$$
FAQ
What does 5/2 mean? You win £5 profit for every £2 staked, in addition to getting your stake back.
How do I convert to decimal odds? Divide A by B and add 1. So \(5/2 = 2.5 + 1 = 3.5\).
Does implied probability include the bookmaker margin? Yes — the implied probabilities across all outcomes usually sum to more than 100%, reflecting the bookmaker's overround.
