The odds conversion between fractional, decimal and American betting odds is a fairly simple process once you understand how they are used to display the information you need when making a bet.
Fractional odds are most familiar to punters in the UK when they visit the bookies or bet at an online sportsbook. However, many sites now offer the chance to let you see decimal odds, which are popular across Europe, and some also offer American odds, or moneyline odds as they are also known.
Prices like 4/1 display the bookmaker’s calculated probability of that event happening, as well as the payout you can expect if you back the correct outcome. Essentially it represents that you will win once for every four times you lose at these odds. You can also ascertain that you will receive £4 back in profit for every £1 staked.
By the same token, a less well-fancied horse at 10/1 is considered likely to lose ten times for every race it wins, but your £1 stake will return £10 in profit in recognition of the lower probability of the bet coming off. With fractional odds, you receive your stake back, in addition to the profit shown in the price, if you win.
Sometimes you find a price such as 1/3, which is known as ‘odds-on’. A tennis player at these odds is deemed to be very likely to win because bookies feel they will only lose once for every three games in which they succeed. With an odds-on price, you can see that you have to stake £3 in order to receive £1 in profit. You will also have your £3 stake returned if it is a winning bet.
The decimal equivalent of 4/1 is 5.00, representing the number you multiply your bet by to calculate your winnings, including the return of your initial stake.
To convert fractional odds to decimals, you simply divide the first number by the second and add 1.00. For example, 4/1 = 4, add on the 1.00 and you have 5.00. A less-straightforward set of odds would be 3/2 = 1.5, add on the 1.00 and you have 2.50.
Many people prefer decimal odds because it is easier to tell at a glance that 2.50 is more profitable than 2.40, than it might be by using their fractional equivalents, 3/2 and 7/5.
If you want to convert decimals to fractional odds, you subtract the 1.00 and find the lowest whole numerator for the fraction. For 2.50 you subtract the 1.00 and are left with 1.5/1, or 3/2 expressed in whole numbers.
Some sportsbooks, like William Hill and Paddy Power, give you the option to display their prices as American odds. A number with a + before it shows what you would win if you bet £100 and a number preceded by a - shows how much you have to stake to see a return of £100. This means that 4/1 in fractional odds (5.00 in decimals) works out at +400 in American odds.
To convert American odds to decimals, you divide + numbers by 100 and add 2.00 or divide 100 by a - number (discarding the -) and add 1.00.