Odds and Percentages

Understanding how odds work is the first step you should take in educating yourself about the betting game. There are three types of odds that you may come across:

Chance odds – This type of odds expression is also used to indicate the likelihood of a certain event or occurrence, but is more commonly found in probability calculations than in a betting shop. This type of odds expression is best explained by looking at the probability involved in a standard dice roll. There is 5/1 chance of rolling a 1 on your first throw (five chances against, with only one potential successful outcome). Meanwhile the odds of throwing a 1,2 or 3 are 3/3 (three chances against, with three potential successful outcomes). This can be factored down to become 1/1 or evens.

Payout odds – In most sports, true chance odds are unknown, as there are usually far too many factors and variables to be able to accurately calculate the real chance. However, there are a great many organisations that are highly skilled in assessing sporting competitions, who are adept at assigning estimates of the chance odds. These estimates are then used by bookmakers, who offer different odds that are based on the estimates of the chance odds, but which are slightly inferior, so as to allow them to make a profit.

Payout odds can themselves be shown in one of three different ways:

• Fractional odds - The odds are expressed in a way that shows the potential winnings for any given stake. For instance, odds of 3/1 meant that you would win 3 units for every 1 unit staked. Sometimes the odds take a slightly different form, to ensure that only whole numbers get used. For instance odds of 3/2 mean that you will win 3 units for every two units staked, which is actually the same as winning 1.5 units for every unit staked. Calculations using fractional odds give you your profit (i.e. your winnings excluding your stake), so your stake needs to be added back in to calculate your total return.
  
• Decimal prices - Some bookmakers use decimal odds, where the odds are simply expressed as the winnings from one unit. Where this is the case, there is no restriction on the use of whole numbers, so you might see the odds expressed simply as 2.33 or 5.50, which equate to 7/3 and 11/2 respectively. Decimal odds provide the simplest way of calculating your total return, i.e. your winnings including your stake.
  
• US Prices – These are commonly used in North America and Canada when betting on US sports. To calculate the Payoff on US Prices, convert the US Prices to decimal prices as follows:
  - for a favourite, for example -1.25, divide 100 by 125 and add 1 = 1.80
  - for an underdog, for example +1.25, divide 125 by 100 and add 1 = 2.25

Percentages - Unless decimal payout odds are being used, comparing the returns from different odds in not necessarily that easy. For instance, how many people would be quickly able to tell the difference between 9/5 and 13/8? Probably not that many, since the odds are on different incremental scales. For this reason, percentages can be used as a common scale in order to assist the visualisation of chance and to ease any arithmetical calculations you need to make.

The percentage scale is quite easy to use, as it is fairly familiar – most people know that 100% chance equals certainty, while 0% chance equals no possibility. The scale of possibilities in between are known as percentage probabilities or percentages. Odds can be converted to percentages by dividing the right number by the sum of the left and right numbers, for example, 3/3 or 1/1 equate to a percentage of 50% (3 divided by 6 or 1 divided by two). To calculate the odds from a percentage, you need to divide 1 by the decimal fraction and then deduct 1. So 25%, which is the same as the decimal fraction 0.25 would be come 3/1 (1 divided by 0.25 equals four, minus one equals three).

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