How do Random Number Generators work?

Live dealer has largely removed the need for simulated random outcomes for online casino games. The use of physical gaming equipment – real cards, roulette wheels and dice produce truly random outcomes.

But if you want to know how computer generated outcomes are randomised playing traditional online casino games, you need to understand random number generators.

What’s a Random Number Generator?

Random Number Generators (RNGs) are the digital backbone of online casinos, ensuring games like slots, blackjack, and roulette produce fair and unpredictable outcomes. Because of the crucial role played by RNGs, these games are commonly referred to as ‘RNG games’.

RNGs act like a digital ‘luck machine’, determining game results (e.g., slot symbols, card shuffles, roulette spins) in a way that mimics chance outcomes. Think of an RNG as a digital dice roller with the outcome determined algorithmically rather than physically.

The RNG generates random numbers which are then mapped to game specific outcomes – the symbols on the reels of a slot, the card value and suit for a game of blackjack, or the the number 0 through 36 for a game of roulette.

What are the main types of RNG?

There are two main types of RNGs, each working very differently to achieve randomness – Pseudorandom Number Generators (PRNGs) and True Random Number Generators (TRNGs).

Pseudorandom Number Generators

• How They Work:
  PRNGs use algorithms and a starting point called a “seed” to generate random number sequences. The seed acts like a secret code—if you know the seed and the formula, you can reproduce the same sequence of numbers. However, casinos and software developers keep the seed hidden on a secure server and refresh it often (e.g., using the exact time you click a button) to make results unpredictable. PRNGs are able to generate numbers randomly in a sequence that doesn’t repeat itself for a very long period of time.
• Example: Mersenne Twister’s version MT19937 is a famous PRNG, with a period length of 2¹⁹⁹³⁷ (a number with 6,000 digits). This means it won’t repeat the same sequence for trillions of years, even if you generate millions of numbers per second.

PRNGs are the preferred RNG method employed by online casinos. They are fast, cost efficient, deployable at scale and easy to audit (auditors can replay the sequence with the seed to verify fairness).

On the downside, they are not truly random. Because outcomes are produced by a mathematical formula they are deterministic, albeit entirely unpredictable and secure as long as the seed is kept secret.

True Random Number Generators

• How They Work:
  TRNGs rely on physical processes in the real world to generate randomness, such as atmospheric noise, radioactive decay, or even the static from a microphone. These phenomena are inherently unpredictable.
• Example: Imagine rolling a dice in a wind tunnel where gusts change the outcome—TRNGs measure natural chaos to create numbers.

TRNGs are truly random (no patterns or predictability) with no need for seeds or algorithms. On the downside, they’re slower and more expensive (requires specialised hardware), practically impossible to deploy at mass scale, and harder to audit (can’t reproduce the same sequence).

Hybrid RNGs (HRNGs)

Hybrid systems combine PRNGs and TRNGs. For example, a TRNG might generate a seed for a PRNG, mixing natural randomness with mathematical efficiency.

RNGs Used by Major Casino Software Developers

PRNGs dominate in online gaming because they’re fast, cost-effective, and auditable. While not truly random, they’re secure enough when properly implemented (hidden seeds, frequent reseeding). TRNGs are occasionally used to seed PRNGs in hybrid systems, adding an extra layer of unpredictability.

While specifics about proprietary algorithms are rarely disclosed publicly, regulatory filings, audits, and technical documentation provide insights into their RNG systems.

Below is a simplified comparison of how top developers implement RNGs:

Developer	RNG Type	Key Features	Auditors	Example Games
Playtech	PRNG + TRNG seeding	Combines math formulas with real-world randomness (eg. server data). PRNG combined with cryptographic hashing (eg. SHA-256) to enhance unpredictability.	GLI, NMi	Age of Gods Slot
RTG	Proprietary PRNG	Updates the “seed” frequently using player actions (eg. mouse speed).	iTech Labs, TST	Cleopatra’s Gold Slot
Microgaming	PRNG (Mersenne Twister)	Based on the Mersenne Twister algorithm, known for its long periodicity (~2^19937 outcomes), generating trillions of numbers before repeating.	eCOGRA, Quinel	Mega Moolah Progressive Slot
NetEnt	PRNG + encryption scrambling	Adds security layers, like shuffling numbers using password-like encryption.	GLI, eCOGRA	Starburst
Light & Wonder	PRNG + hardware entropy	Reseeds regularly with real-world data (eg. server signals).	BMM Testlabs	88 Fortunes Slot

Relationship between RNGs and game theoretical returns

A game’s theoretical return is determined independently to the PRNG generating that game’s random outcomes.

The PRNG will spit out random numbers (mapped to card values, symbols etc) to ensure random outcomes each virtual spin, roll or deal. But returns will depend on the game math underlying the game.

For a game of European Roulette for example, the PRNG will ensure randomness in the 37 possible numbers (0 through 36) that result for a given spin. It is the probability of win (1 in 37) and set payout (35:1) that produce a house edge of 2.7% or RTP of 97.3%. The same PRNG method employed on an American Roulette game will result in a different RTP of 94.74% because an extra number on the wheel changes the win probability to 1 in 38. It’s game design, not the RNG that dictates return.

Similarly for slot games where RTP is predetermined, the PRNG doesn’t “know” the RTP—it just ensures random appearance of symbols. RTP is fixed because the probabilities are baked into the game’s design. For example, a slot with 95% RTP might allocate 5% of all possible PRNG outcomes to “losses.” Over millions of spins, the average payout converges to 95%.

For skill games like blackjack, game’s ruleset and player decision making determine the RTP. The PRNG just shuffles the virtual deck and deals cards randomly.