Odds and Probabilities

gambling mathsCasino and gambling can be a lot of fun, especially when players do not understand the mathematics behind it, but being aware of these matters would offer players more fundamental understanding of the way probabilities and odds work.

Odds and probabilities are some of the most important aspects of gambling mathematics. They could be related even to the pay-off of a certain game. For example, there is an even money situation when it is explained that a bet pays off at the same odds as the probability of winning the bet.


Probabilities are often described as the very backbone of gambling mathematics.

Informally, probability is understood as the chance or the likelihood that a certain event will happen. It is also considered to be an estimate of the corresponding average frequency that is applied for a certain event to occur in a series of independent trials that have been repeated.

The relative frequency of an event is somewhere between the probability of the event never to occur or always to occur, which basically means that it is always between 0% and 100%. Knowing how to use the probability would provide casino players with the opportunity to predict the eventual occurrence of an event. Unfortunately, it would not give them the chance to predict the exact moment when the event is to occur.

In addition, probability in gambling mathematics can be used when determining the conditions for acquiring certain results or even some financial expectations of a game in particular in the long term. Probabilities could also be helpful when determining how favourable a certain game would be and is it worth playing. This aspect of the matter is usually expressed as odds, as well as a fraction or a decimal fraction. Still, casino players should be aware of the fact that odds and probabilities are different things.

The estimate of the likelihood of a player winning divided by the total amount of available chances is called probability. The latter is also an ordinary fraction that can be expressed as a proportion between 0 and 1, or as a percentage.

What casino players should understand first is the formal theory of probability and are recommended to start with the term that is known as the “sample space”. It may sound somehow strange, but as a matter of fact, this is purely a description of all outcomes possible, or other words – of everything that can possibly happen. It is quite normal for sample spaces to be very large when it comes to casino games. As a matter of fact, they simply reflect the idea that too many things could actually happen to count them all.

The sample space is something that may occur in a large number of experiments and can normally be understood easily when considering the nature of the experiment. Still, the sample space does not have to be described in a explicit way.

Players will need be aware of some details in order to calculate the probability of a certain event. First, they will need a full count of the number of individual elements in the sample space. In addition, they will need to know the number of the individual elements related to the event. Once a player knows these values, they will be able to define the probability of the event by using the equation:

P(event) = Size of event / Size of the sample space

As shown in the equation, the letter P is used as a substitute of the word “probability”. What is not so evident by the above-mentioned equation is how the player should count the size of a variety of collections. Unfortunately, the counting problems in the gambling industry can be too complex. Of course, probabilities can be quickly calculated when counting is easy.

player wagering a stack of chips


The most general definition of odds is the probability of a certain event happening in comparison to the probability of the same event not happening.

Odds are considered as ratios of the player’s chances of losing to the likelihood of winning. In other words, they are the average frequency of a player’s eventual loss to the average frequency of a win. As already mentioned above, odds are often mistaken with probabilities, but they are not the same thing.

As a matter of fact, odds almost never mean the actual likelihood of generating a win when it comes to gambling. In most cases, the term is used as a reference to a subjective estimate of the odds, and not as an exact mathematical calculation.

For example, if a player owns 1 of a total of 4 tickets, their probability to win is 1 in 4. Their odds, on the other hand, are 3 to 1. In order for a player to convert odds to probability, they need to take the likelihood for them to win, then use it as the numerator and divide by the total number of chances, including the ones for both winning and losing.

For example, let us take that the odds are 4 to 1. Then, the probability would be found by using the following equation:

1 / (1+4) = 1/5

In other words, the probability in this case would equal to 1/5, or 20%. What players need to know is the fact that the so-called “evens” are odds of 1 to 1. They are always paid even money.

The term “odds” could also be used as a substitute of the true odds that are the actual chances of winning. There are also payout odds, which represent the ratio of payout for each unit bet.

Just like probabilities, odds can also be expressed as a ratio of two numbers. The first number comes to represent the expected frequency of the occurrence of a specific outcome, and this is actually exactly what probabilities are. The second number, however, represents only the number of the rest of the possible outcomes. In comparison to probabilities, which could be expressed as percentages, odds are always displayed as ratios.

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