Every card dealt and every spin of the reels in online casinos depends on random numbers. But how are these numbers actually created, and why does it matter for fair play?
This guide explains what a Random Number Generator (RNG) is, the difference between Pseudo-Random and True Random systems, and how outcomes for slots and card games are decided.
You will also find a clear overview of UK regulation, independent testing, practical ways to check a casino’s RNG, and the security measures used to protect these systems so games remain fair.
Read on to learn more.
What Is an RNG and Why Does It Matter?
An RNG, or Random Number Generator, is the engine that produces unpredictable results for online casino games. It ensures that each spin, card, or game round is selected independently, without a pattern or pre-set sequence.
RNGs matter because they preserve fairness. By producing outcomes that cannot be anticipated or influenced, they prevent either the casino or players from steering results. In the UK, licensed operators must use certified and tested RNGs to meet regulatory standards.
It is also worth keeping in mind that RNGs do not increase anyone’s chances of winning. Each outcome is separate from the last, so previous results do not affect what happens next.
Types Of RNGs Used By Online Casinos
Online casinos use two main types of Random Number Generators (RNGs): Pseudo-Random Number Generators (PRNGs) and True Random Number Generators (TRNGs).
A Pseudo-Random Number Generator, or PRNG, is a computer algorithm that quickly produces numbers that behave like random results. PRNGs use a starting value called a seed and follow a set process to generate sequences that are unpredictable in practice. Most online casinos use PRNGs because they are fast, reliable, and do not require extra hardware.
A True Random Number Generator, or TRNG, works differently. It uses physical processes outside the computer, such as electronic noise or atmospheric data, to create numbers. TRNGs can provide additional unpredictability but are less common online because they need specialised equipment.
Both types must be tested to confirm they deliver fair results under UK rules. With the types in mind, it helps to see how the one most sites rely on actually works.
How Do Pseudo-Random Number Generators Work?
Pseudo-Random Number Generators, often called PRNGs, are computer programs used by most online casinos to create outcomes that appear random.
A PRNG starts with a seed number, chosen automatically by the system. This seed acts as the starting point for the algorithm that generates the sequence of numbers. The outcome of each game round is tied to the current value in that sequence at the exact moment it is requested.
Although PRNGs are mathematical rather than physical, they produce results with a high level of unpredictability. The system cycles through enormous sequences many times per second to prevent patterns from forming and to ensure results are not repeatable in a way that can be exploited.
For online casino games, this process runs continuously in the background. Regulators require PRNGs to be independently tested to confirm that the output meets strict standards for randomness and fairness. With that foundation, it is useful to compare PRNGs with systems that draw on physical events.
What Is a True Random Number Generator?
A True Random Number Generator, or TRNG, is a system that creates random numbers using natural or physical events rather than computer instructions.
TRNGs detect unpredictable activity in the physical world, such as electrical noise, and convert it into numbers. Because these inputs cannot be forecast or repeated in the same way, TRNGs provide randomness sourced from outside the software itself.
In online casinos, TRNGs may be used in specialist contexts, but PRNGs remain the standard due to performance and practical demands. Both approaches aim for the same goal: outcomes that cannot be foreseen or influenced.
Knowing how the numbers are produced sets the scene for how they are mapped to reels and decks in real games.
How Do RNGs Determine Slot And Card Outcomes?
Online casinos use RNGs to produce outcomes for both slots and card games in a way that keeps results independent from one round to the next.
For slot games, the RNG continuously generates numbers. When a player presses spin, the software takes the current number from the RNG and maps it to specific symbols on the reels. Each spin is self-contained, so previous outcomes have no influence over the next result.
For card games, the RNG is used to shuffle and deal. The system assigns a random order to a virtual deck before a hand or round begins. That prevents predictable patterns and means no one can know which card will be dealt next.
These methods ensure outcomes are produced fairly without input from players or the casino. The timing of when a request hits the RNG determines the exact result that appears.
How Often Do RNGs Generate Numbers During Play?
Random Number Generators run constantly in the background of online casino systems.
For most games, the RNG cycles through values many times per second, regardless of whether a player is active. When a player acts, such as pressing spin or drawing a card, the game software uses the current RNG output at that moment to determine the result.
No two rounds are connected. Each outcome is generated from a fresh point in the sequence, which supports fairness across every session.
Are RNGs Audited And Regulated In The UK?
In the UK, online casinos must use fair and reliable RNGs for all their games. The UK Gambling Commission sets the requirements and oversees compliance.
Licensed operators have their RNG systems assessed before games go live. Regular audits follow to confirm that the RNG continues to meet technical standards and that game outcomes remain within expected statistical ranges over time.
How Testing Labs Check RNGs
The UKGC recognises independent testing labs to carry out these checks. These specialist organisations review the casino’s software, including the RNG, and verify that it behaves as intended.
Labs run large volumes of simulated rounds, analyse the distribution of outcomes, and check that previous results do not affect future ones. They also confirm that any seeding or reseeding works correctly and that the implementation matches the technical specification.
Only when an RNG passes these tests can it be used in live games, and periodic reviews are performed to ensure standards are maintained. If you want to see this in practice, the next section shows how players can verify a site’s claims.
How Can Players Verify a Casino's RNG Is Fair?
Players can check a casino’s RNG by looking for clear signs of regulation and independent oversight.
Start with licensing. A valid licence from the UK Gambling Commission indicates the operator must use tested RNGs and meet technical standards. Most reputable sites also link to certificates from independent testing agencies such as eCOGRA, iTech Labs, or GLI. These certificates often sit in the website footer or a page dedicated to fairness or security and may include summaries of recent audits.
Some casinos provide clickable audit seals or publish outlines of their testing schedules. If details are not easy to find, customer support should be able to confirm which labs assess the games and when checks were last completed. If a site cannot provide this information, it may be wise to look elsewhere.
With verification covered, a common question follows: could someone interfere with the generator?
Can Online Casinos Manipulate RNGs?
UK-licensed online casinos must keep their RNGs fair and unbiased, and they are subject to strict supervision by the UK Gambling Commission. Independent laboratories regularly test the software to confirm that outcomes remain random and that no hidden patterns appear. Deliberate manipulation would breach licence conditions and could lead to serious sanctions.
By contrast, unlicensed sites may not follow these standards. Checking for a valid licence and recent testing certificates reduces the risk of encountering unfair practices and gives players stronger protections.
With fairness requirements in place, operators also protect the systems themselves from interference.
Security Measures Protecting RNGs
Online casinos use several layers of security to protect their RNGs from tampering or unauthorised access. Secure servers and strong encryption shield the software. Access controls restrict who can view or change code, and any changes are logged and monitored. Technical teams follow change-management procedures so updates are reviewed, tested, and documented before release.
Security audits complement regulatory checks. These reviews assess both the code and the surrounding infrastructure, looking for vulnerabilities and confirming that access rules are followed. Combined with independent randomness testing, these measures help ensure games run as intended.
If gambling no longer feels manageable or begins to affect your well-being or finances, support is available. Services such as GamCare and GambleAware offer free, confidential help. Understanding how RNGs work, and choosing properly regulated sites, helps keep play informed and fair.
**The information provided in this blog is intended for educational purposes and should not be construed as betting advice or a guarantee of success. Always gamble responsibly.