Why Are Odds Relevant in Different Casino Games?

Why Are Odds Relevant in Different Casino Games?

Published Date · March 30, 2021 · Last Updated · June 23, 2023 ·Read Time · 5 mins

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Whilst the concept of betting and gambling has been around for centuries, the invention of the internet and the accompanying acceleration of its capabilities has allowed online casinos and betting establishments to reach a much wider audience. As a result, the necessity to interpret and understand how betting odds work in order to maximise your chance of winning has become even more prevalent in modern society for those looking to increase their gaming experience. Whilst you might find yourself with a casual understanding of some of the simpler odds formats available, you will be forgiven for thinking that casting your eyes over various betting sites can appear quite intimidating when faced with a plethora of fractional and decimal odds. In short, betting odds represent a visualisation of the probability that an event will occur. For example, at a roulette table, if you are betting that the ball will land in the number 17, you are betting on the likelihood of that happening. Needless to say that this has the potential to be relatively confusing.

As a result, we have compiled an overview of the most relevant and important aspects of understanding odds and their relevance within different casino games to help you understand your chance of winning.

How Odds Can Be Displayed

The primary notion when understanding how betting odds work is to note that there are fundamentally three main methods of displaying them;

Fractional Odds – Fractional odds are presented as two numbers, separated by a / i.e. 1/2. If the first number (numerator) is larger than the second number then the event is considered to be odds against (more likely not to happen). If the first number (numerator) is smaller than the second number, it means the event is more likely to happen than not. This is otherwise known as ‘odds on’.

Decimal Odds – Decimal odds are presented as a decimal (a percentage divided by 100). You can convert your odds to a decimal from a fraction by adding the fraction together. For instance, odds of 20/1 can be converted by adding 20+1 = 21.00. To work out the implied probability, you can take (1/decimal odds) x 100.

American Odds – American odds are portrayed as a number with a plus or minus in front. In its’ simplest form, an event being listed as +500 means that you will receive £600 from a £100 stake (£500 winnings plus your original stake). A plus sign indicates that this is more likely not to happen than would. A negative sign in front of the number such as -300 means that the event is more likely to happen than not and that you would need to stake £300 in order to win £100 (£400 in total).

Odds Will Often Remain the Same for Most Casino Games

It is important to remember that whilst odds will remain the same for most casino games that you will find yourself playing online. Whilst most people will have experience of seeing odds in relation to a sports betting fixture that can subsequently fluctuate whilst that very match is being played, most casino games are bound by a uniform structure of probability.

As a result, the odds will not change during casino games such as blackjack or roulette. As you are betting on the likelihood of an event occurring, the boundaries of the game such as a limited number of cards to be drawn or numbers to land on, restrict the realm of possibilities that may occur.

In blackjack, whilst there are a limited number of cards to be drawn, the starting odds will remain the same however the probabilities fluctuate as the deck changes with every card that is removed from play.

For roulette, there are a limited amount of numbers on which the ball can land (37 on the European version) which gives you a 1 in 37 chance (2.70%) of selecting the correct number on which that ball will land. Some systems of betting allow you to bet on more than a single number, giving you a greater chance of selecting a correct number however decreasing the amount of money that you will win as a result.

Slot games, ever popular within online casinos, are a lot more unpredictable and vary considerably from game to game. Each are dependent on their own Random Number Generator and the Return to Player Percentage. As a result, they can be a lot harder to win money on over a longer time and have far greater variance in their probability of paying out.

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House Edge

Whilst the relative simplicity with which the probability can be factored into account when wagering a bet, it is important to remember that, at the end of the day, a casino in any format is a business and thus needs to operate with a profit margin. To this end, a ‘House Edge’ is incorporated into the probability. If we return to our roulette example, on the European version, the House Edge is 2.70%. On the American version, there are two zero pockets, increasing the wheel to 38 numbers and increasing the house edge to 5.26 percent (2 in 38 chance).

Bigger Odds Mean Something is Less Likely

Whilst calculating the probability of an event occurring, the simple rule is that the bigger the odds, the less likely it is to happen. Casino odds are calculated as a result of understanding a rough likelihood that an event will happen. In sports, this can be articulated as simply as a team winning a particular game. In order to identify the odds of this occurring before the event, experts will look at a number of factors such a the teams’ form, potential injuries and overall quality.

In relation to a specific casino game, this can be a considered as a ‘long-shot’ and more often than not, will result in no return. Identifying your 1-in-37 chance of winning at roulette would sufficiently fall into the category of a long-shot however this can be extended even further in certain games. Whilst this would not be advisable for a sustainable method of gambling, winning a bet from long-shot can be an exhilarating feeling.


Whilst online casino sites display their odds as fractions, many provide the opportunity to display them as decimals to save you completing multiple calculations every time you wish to place a bet. You certainly don’t need to become a mathematical genius to work out odds, the importance of understanding that you are simply identifying the probability of an event occurring is crucial to identifying the most important aspect of all; what are your potential winnings and what is the likelihood of you winning it!


Phoebe Greenwood

Content Writer