Betting odds are at the centre of sports betting. Without odds there is now way of knowing what your return will be on a bet or indeed whether the potential return bears any relation to the (perceived) probability of a particular event occurring.

Betting odds are very much linked to probability, but are not always accurate representations of the actual probability of an event for the simple reason that, in sport, it is almost impossible to ascribe an accurate probability to, say, a correct score in a football match due to so many confounding variables.

Added to that, bookies will always build a “margin” into their odds to give themselves a profit; thus, were they to lay odds on the toss of a coin (as they basically do when taking bets on which side will win the toss in cricket) they don’t offer odds that are representative of the possible outcomes, that is evens (or 1/1 or 2.00); rather they offer something slightly less such as 10/11 or even as low as 5/6 at some of the less scrupulous bookies.

Odds are expressed in a variety of ways including the traditional fractional odds, decimal odds (popular in much of Europe as well as Australia) and American odds used by our cousins across the pond. Read on for the main features of each and the differences between them.

## Fractional Betting Odds

Fractional odds are the primary type used in the UK and were basically the only kind you would find until betting exchanges appeared using decimal odds. Fractional odds are expressed – surprise, surprise – as a fraction, so a horse might be priced at odds of 10/1 (known as “10 to one”) to win the Grand National, which means that you would get a profit of £10 for every £1 you staked if the horse wins, and your stake would be returned with the winnings. Hence if you placed a £5 bet on the horse and it romped home your payout would be £55.

If the odds show a smaller number on the left of the fraction than the right (for example 4/6 or 10/11) you will receive less profit in your winnings than the value of your stake (though profit it will still be given your stake is returned). So if you bet £20 at odds of 4/6 and your selection came in you would receive a total payout of £110.

Odds of this sort are known as “odds-on”, as opposed to the “odds against” odds when the figure on the left is greater than that on the right, so 4/6 can be known as either “four to six” or “six to four on”. When you get a profit equal to your stakes, the odds are said to be “evens” or “even money” but are occasionally written as 1/1.

## Decimal Betting Odds

Next we come to decimal odds which, as mentioned, are favoured in Australia, many European countries and also the betting exchanges such as Betfair. The number which represents the odds is expressed as a decimal (such as 2.00, 1.9!, 3.62) and can be worked out by converting fractional odds to a decimal and adding one.

As such, odds of 4/6 in fractional form work out to be 1.67 (to two decimal places) when represented in decimal odds format. Conversely, to work out the fractional odds from a decimal, minus one and convert to a fraction, so decimal odds of 3.75 would be 11/4.

Evens (or 1/1) works out at 2.00 in decimal format, so any odds less than that value are odds-on and any that are greater are odds against.

## American Betting Odds

American odds are slightly different as they incorporate a “+” or “–” sign to indicate what profit you would win if you either placed a $100 stake (the “+”) or how much you have to stake to win $100 (the “–” ).

As such, using the example odds of 4/6 (or 1.67 in decimal), would give American odds of -150. While 10/1 (11.00) would be +1000, and 10/11 (1.91) would be -110. Evens (2.00) are generally known as “even money” in the US and would be represented by American odds of +100.