Odds calculator
Convert between fractional, decimal, and American odds. Calculate potential returns, profit, and implied probability from any bet.
Returns
£60.00
Profit
£50.00
Implied probability
16.67%
Fractional
5/1
Decimal
6.00
American
+500
Quick odds
How odds work
Betting odds represent the probability of an outcome happening — and the payout you'll receive if it does.
Fractional odds (e.g. 5/1) are the UK standard. The first number is what you win, the second is what you stake. At 5/1, you win £5 for every £1 staked.
Decimal odds (e.g. 6.00) show your total return including stake. Multiply your stake by the decimal to get total returns.
American odds use + for underdogs and − for favourites. +500 means £500 profit on a £100 stake. −200 means you stake £200 to profit £100.
What is implied probability?
Implied probability converts odds into a percentage chance of winning. At 5/1, the implied probability is 16.67% — meaning the bookmaker prices that outcome as having roughly a 1-in-6 chance.
This is useful because it lets you compare the bookmaker's assessment with your own. If you think an outcome has a 25% chance but the implied probability is only 16.67%, that's potentially a value bet.
Why odds don't add up to 100%
If you add up the implied probabilities of all outcomes in an event, they'll total more than 100%. The excess is the bookmaker's margin (or overround). For example, a coin flip should be 50/50, but a bookmaker might offer 10/11 on both sides — giving each outcome a 52.4% implied probability, totalling 104.8%.
That 4.8% is the bookmaker's built-in profit. Our house edge calculator lets you compare margins across games.
Understanding betting odds
How to read fractional odds
Fractional odds like 5/1 (spoken as 'five to one') tell you the profit relative to your stake. The number on the left is your potential profit, and the number on the right is the amount you need to stake. At 5/1, a £10 bet returns £60 — that's £50 profit plus your £10 stake back.
Odds-on prices like 1/2 mean the outcome is more likely than not. At 1/2, you stake £2 to win £1, giving total returns of £3.
How to read decimal odds
Decimal odds show your total return for every £1 staked. Odds of 6.00 mean a £1 bet returns £6 (£5 profit + £1 stake). Decimal odds of 1.50 mean a £1 bet returns £1.50 (50p profit + £1 stake).
The key advantage of decimal odds is simplicity — multiply stake by odds to get returns. No mental arithmetic needed.
How to read American odds
American odds use positive and negative numbers. Positive odds (+500) show how much profit you make on a £100 stake. Negative odds (−200) show how much you need to stake to make £100 profit.
Most UK punters won't encounter American odds often, but they're standard in the US and appear on some international betting exchanges.
Converting between formats
All three formats express the same thing — just differently. Our calculator converts between them automatically, but here's the quick maths:
To go from fractional to decimal: divide the first number by the second, then add 1. So 5/1 = (5 ÷ 1) + 1 = 6.00.
To go from decimal to implied probability: divide 1 by the decimal odds and multiply by 100. So 6.00 = (1 ÷ 6) × 100 = 16.67%.