How Online Casinos Ensure Fair Play With Rng

How Online Casinos Ensure Fair Play with Random Number Generators

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Updated on: 5 Apr 2024
Dean McHugh

A random number generator, also known as RNG, is the method by which casino games like slots can ensure that the outcomes of each round are genuinely random. An RNG in modern online games is an algorithm that will constantly generate combinations that relate to possible outcomes in any given casino game. All licensed online casinos must ensure that their complete game library is verifiably fair and random. But how does this relate to your gameplay?

Keep reading our guide on how online casinos ensure fair play with random number generators to understand how they affect you and your favourite games.

How do RNGs work in online casino games?

slot machine with random numbers

Random number generators are essential to ensure that games are random and fair. The RNG algorithm determines whether you win or lose a round. Without an RNG, casino games have the potential to be fixed with predetermined outcomes that can result in biased results against the player. A casino game developer is required to integrate a 3rd party RNG algorithm in order to legally provide any game to casino players.

Slot machines originally used machinery to ensure random outcomes. Now, modern machines and online casino games all use RNG algorithms to determine round outcomes. The only exception to this when it comes to online gameplay is live casino games. These are still determined by decks, dice, or the spin of the roulette wheel, depending on the game in question.

Slots and online casino games all use RNG algorithms that have been created by independent 3rd party developers. The algorithm works similarly to a stopwatch that is constantly creating number combinations. Each tick of the clock generates a new mixture of combinations in a random order. Taking slots as an example, the algorithm’s clock will essentially stop as soon as you hit the “Spin” button, with the outcome of the round being immediately determined. Each number combination within the algorithm relates to specific outcomes possible within the game. The visuals you see of spinning reels are animations that have no impact on the actual results of the round.

Fairness and Randomness with RNGs

Fairness and randomness are vital to any casino game and something that gambling authorities take very seriously. Randomness is provided by the RNG, which is a big part of what makes a game fair. Random number generators are developed to ensure that each game round is independent from the last. This means that any previous rounds will not impact the outcome of your active game round. It may be that you notice certain patterns from round to round, but this is purely coincidental. When dealing with randomness, we instinctively try to find patterns. This could include win and loss streaks. However, it is like flipping a coin. Heads may show up more than tales, but that doesn’t necessarily mean the coin is weighted.

Other elements of fairness include transparency of game rules and game odds. Return to player percentages that are found in virtual casino games are controlled by the RNG. These percentages are an average of payouts from that specific game over an extended period of time. On average, a slot game with an RTP of 96% is expected to return 96 coins for every 100 wagered. Sometimes, you may come away with more and other times less, as the RTP is taken from a global average. The RNG controls the RTP by having certain sequence ratios corresponding to winning and losing rounds. This is how different games are able to offer different RTPs.

RNG Certification and Testing

rng testing checkmark

RNG algorithms are created by 3rd party developers to ensure impartiality. The RNG algorithm provided by these developers has to be certified and regularly tested. There are dedicated organisations set up for the purpose of auditing and certifying RNG algorithms used within casino games. Auditing organisations like eCOGRA and Technical Systems Testing are highly trusted and widely used throughout the industry. These organisations ensure that auditing is done on a regular basis and without bias or favouritism.

One of the ways games are tested is by allowing them to complete potentially millions of game rounds, which are compiled and compared with the information provided by the game developer. RNG auditing is a requirement that must be fulfilled by online casinos to retain their gambling licences. Licensing authorities like the UK Gambling Commission and Malta Gaming Authority have strict requirements regarding fairness and player protection. If a site can’t prove its games are fair, it comes at risk of losing its gambling licence.

Compliance and Oversight

In order to comply with regular auditing, online casinos are required, above all, to be transparent. There is a wide range of tests done to ensure a game is fair and compliant. This includes everything from graphics to RTP to any relationship with previous versions of the game or platform. The code behind the games must also be secure so that it is not vulnerable to hacking or any kind of manipulation. Technical Systems Testing and eCOGRA are purely there to test if a game is compliant with current gambling regulations. This is just one of many different types of audits that an online casino is subject to. Other types of audits include responsible gaming and player protection protection procedures.

Online Casino Game RNG Tips

So far, we have touched on the technical side of RNGs, but how can this affect your gameplay? Is there anything you can do to improve your odds of winning? Take a look at these tips to see how you can leverage your knowledge of RNGs to provide you with the best gaming experience possible.

How to Check if a Casino Game is Verifiably Random

Knowing how to check if a casino game is verifiably random is easy and doesn’t require a lot of time. The first step is to ensure that the online casino you are playing at has a valid gambling licence. This is usually displayed at the bottom of the casino site and can be referenced to the licensing authority. The UKGC and MGA sites have full lists of licensed operators that you can check, along with any previous licence violations that may have been actioned. You cannot guarantee that a site will provide fair games if they are not properly licensed.

When it comes to the games themselves, the online casino will have a separate certification seal from a testing authority such as eCOGRA. This seal should also be presented at the very bottom of the casino site, along with their gambling licence information. All games are tested for fairness when an online casino is audited. This means that the casino must be able to show that all games it hosts on its site are fair or otherwise not receive certification. That is why it is not necessary to provide a certification seal on every individual game.

RTP and Volatility

All virtual casino games, including slots, video poker, and table games, must display their RTP somewhere within the game rules. This RTP is a percentage that shows the average returns that are to be expected over an extended period of play. RTP can vary from game to game, so it’s good to know if a game’s RTP is on the low side. The industry average RTP for slot games sits at around 96% to 97% per cent. You would expect that any slot game with a lower RTP would have some interesting and rewarding bonus mechanics to make up for this. Progressive jackpot slots tend to have a lower-than-average RTP, for example.

Volatility is also another parameter that affects the game outcomes in slots. This determines the frequency and value of payouts. Volatility can either be described as low, medium, or high. A slot game with low volatility will pay out often but in smaller amounts, whereas high-volatility slots pay out larger amounts less frequently. There is not a correct answer for what you should play when it comes to volatility. It is simply a matter of personal preference as to whether you would rather wait for bigger wins or are happier with a more steady flow of smaller wins.

Understanding the Difference between True RNG and Pseudo RNG

Technically speaking, there are two types of random that can be attributed to an RNG algorithm. Online casino games provide randomness via pseudo RNG due to the fact that they are required to handle potentially millions of simultaneous game rounds at any given moment. True RNG is too resource-intensive and slow to provide outcomes on such a large scale. Here are the primary differences in how true RNG and pseudo RNG determine outcomes:

  • True RNG - Typically handled physically by a device, truly random RNG uses external factors to provide random results. These factors are unpredictable and can include environmental noises or changes in the pressure surrounding the device to generate different outcomes.
  • Pseudo RNG - Determined entirely by computer algorithms, all virtual online casino games use pseudo RNG to create outcomes. Random sequences of numbers are constantly being generated, with the player determining what sequence will be applied to their game round when hitting the Spin button in a slot game, for example. The sequence of numbers that are applied to the round will determine a specific winning or losing outcome. The term pseudo RNG doesn’t mean that RNG algorithms are flawed in any way. It is simply a scientific term used to distinguish itself from True RNG devices.

Controlling the RNG

The software and code behind online casino games are heavily secured to protect them from manipulation. This means that players are not able to hack into the game to alter the outcomes of rounds to be more in their favour. Equally, online casinos also have no access to the algorithms controlling the games on their site. Online casino games are created by providers, which online casinos can then host on their sites. Casinos do not usually develop the games themselves and have no access to the behind-the-scenes operations of these games. Essentially, this means that online casinos are not able to manipulate the games or their RNGs, and the same game at a different casino will be using the same RNG algorithm.


While we, as players, cannot affect RNG algorithms, it is still a good idea to get an understanding of how they work. As humans, we often look for patterns where there might not be any. This can, unfortunately, lead to some assumptions that may affect our decision-making. When gambling, we want to play with a clear head and the best way to ensure that is by understanding the game we are playing inside and out. We can then rationalise different outcomes and make more informed betting decisions, hopefully providing a clearer path to more fun and successful gaming sessions.

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