This guide is intended for those interested in learning about the mechanics of RNGs in online casinos. It provides a clear explanation of RNGs’ mechanics, the role they play in determining game outcomes of the game, and their limitations. It is based on observations from testing RNGs on both desktop and mobile devices.
Guide Methodology
This guide is based on hands-on testing of online casino games across iOS, Android, and desktop. Observations focus on game mechanics, RNG behaviour, RTP verification, and practical limitations, with attention to responsible gambling and real-world player experience.
About the Author
Scott MacDonald is a casino content specialist who has practical experience playing various games on both desktop and mobile devices. His expertise is based on providing data-driven analysis of the games themselves, odds, and the experience of players, particularly with regard to responsible gambling.
What is a Random Number Generator?
A random number generator (RNG) is a computer-based system that creates random outcomes. RNGs in online casinos control slot machines, video poker, and virtual table and live casino games. The RNG records a number in each round and follows a set of rules to create outcomes.
Pseudo-random vs. true random number generation
The majority of the online casino games make use of pseudo-random number generators. This type of generator uses algorithms to generate a sequence of numbers. Deterministic in theory, unpredictable in practice.
True Random Number Generators make use of physical phenomena. Though they are not commonly used online, some casinos make use of a combination of PRNGs and TRNGs. PRNGs used in certified online casinos are considered to be random and untampered.
How game outcomes are determined
The RNG generates a number, which the software maps to an outcome according to the game rules. This number is what the software uses to determine the outcome. With slots, the outcome is what determines the placement of the symbols on the reels. This outcome is determined the moment the spin is started or the moment the hand is started. The animations are just visual aids.
RNG Certification and Independent Testing
The fairness of RNG cannot be tested over a short period of play. Independent testing labs test the systems using statistical analysis, code review, and extended simulations.
What the Labs Check
- Algorithm: The sequences are fair and random, without bias
- Implementation: The code works correctly without any errors
- Statistical Distribution: Results conform to the theory over millions of rounds
- Unpredictability: Past results do not determine future results
- Resistance to Manipulation: External influences or player actions cannot affect results
Testing Standards and Agencies
Certification bodies like GLI, eCOGRA, iTech Labs, BMM Test Labs, and Gaming Associates certify RNG systems against a set standard (e.g., GLI-19). This is a point-in-time verification; continuous verification requires periodic re-testing, which most reputable operators do.
What RNG certification does and doesn’t guarantee
Does: Verifies that the RNG indeed provides unpredictable and fair results.
Doesn’t: Ensure overall fairness in the casino, a high RTP for the player, timely withdrawals, reasonable terms, or robust regulations.
A casino might have restrictive bonuses or a limited selection of games despite having a fair RNG. RNG fairness is just one aspect that a trustworthy casino must have.
Common Misconceptions About RNG and Randomness
Several persistent myths about RNG operation can lead to misguided play decisions and unrealistic expectations.
Machines are “hot” or “cold”
Each round is independent. The RNG has no memory of previous results, so a game is never “due” to pay out, nor will it continue paying after a win. Past results do not predict future outcomes.
Long losing streaks indicate rigged games
Consecutive losses are normal in high-volatility games. For example, a slot with 96% RTP can produce many losing spins without indicating any tampering. Detecting genuine RNG issues requires large-scale statistical testing.
RTP guarantees session outcomes
RTP is calculated over millions of rounds across all players. Individual sessions can result in total loss or occasional big wins. Short-term results are driven by variance, not RTP.
Bet size or timing influences results
RNG outcomes are independent of bet size, time of play, or betting patterns. Changing bets or playing at different times does not affect probabilities.
Responsible Gambling Considerations
Understanding RNG operation is valuable for informed play, but it’s important to recognize what this knowledge does (and doesn’t) mean for gambling outcomes.
RNG fairness doesn’t change house edge
Despite the use of certified fair RNGs in all casino games that have a house edge, the net result for players is a guaranteed loss in the long run. The randomness only guarantees unpredictability and not profitability. Knowing how RNGs work won’t change the odds, but it can reassure players.
When RNG understanding matters
RNG knowledge is most valuable for:
- Determining the trustworthiness of a casino: The availability of RNG certification from a trustworthy source is one criterion for judging the trustworthiness of a casino
- Preventing superstition-based betting: Knowledge that the outcomes are based on RNG helps prevent superstition-based betting like betting on hot or cold machines, based on due or overdue payouts, etc.
- Forming realistic expectations: Knowledge that outcomes are based on RNG rather than RTP helps prevent a player from chasing losses or expecting a high return on a bet based on normal fluctuations in statistics
FAQ
The RNG makes use of algorithms that produce a sequence of numbers that cannot be predicted. The spin process records the current number and aligns it with the reels based on the programming. The results are determined at the start of the spin and not during the animation process.
Yes, independent testing labs verify RNGs through statistical testing, source code reviews, and millions of simulated game rounds. Players are not able to verify the RNGs on their own. This is because verifying the RNGs requires specialized knowledge and the source code of the game.
The RNG is responsible for unpredictable outcomes of each game round. RTP, or Return to Player, is the theoretical value of wagers paid back over millions of rounds. The RNG ensures randomness in meeting the RTP but is not responsible for determining the RTP value itself.
No. Each game is a random event. The RNG has no memory. The results of previous spins do not affect the outcome of the next spin. Beliefs about “hot” or “cold” machines are cognitive biases.
RNG certification ensures the technical standards are met for the random number generation of a game. It does not guarantee fair bonuses, safe withdrawal systems, or the integrity of the operator.
