Random Number Generator (RNG) in slots explained

When playing slots, you might sometimes experience feelings of hot or cold streaks.

When things are going well, it feels like the slot can’t fail you as you keep hitting wins and triggering bonus games more frequently than expected.

Other times, it feels like the slot is ice-cold, and you can’t win no matter how many spins you play.

Well, the truth is that it is all completely random, and there is no such thing as hot or cold slots, as every single spin is entirely based on a Random Number Generator (RNG) algorithm.

This article will explain exactly how it works and how they are tested. We will also go through commonly asked questions about RNGs. 

how does the random number generator work

How does the Random Number Generator (RNG) in slots work?

To ensure that online slots are fair and luck-based, these games use a Random Number Generator (RNG), a computer algorithm that generates a number between 0 and 4 billion hundreds of times a second.

This function produces a random number on every single spin, no matter the outcomes shown on previous spins. This particular number correlates to an outcome, which is then visualized on the reels of the slot.

Some examples:

  • Number 1,000,001: outcome = 0 times your stake.
  • Number 10,034,006: outcome = you win 0,5x your stake (i.e., you lose half your stake).
  • Number 50,003,000: outcome = you win 250x your stake.

To ensure the casino has a house edge over the player, there are lots of losing or small wins, and just a few big wins. The outcome can be shown as a line win, as a mystery win, or as a bonus game.

The algorithm is stored on a gaming server hosted by the game developer or a third party and can’t be influenced once held there.

The game studio creates the RNG algorithm, an essential part of the slot’s setup.

Online slots are then tested and approved by licensed third-party companies before the games can be used by online casinos and offered to players.

How is the Random Number Generator tested?

Once a new slot has been created and considered ready by the game studio, it needs to be sent over for testing and receive approval from a licensed third-party company or institution that specializes in this field.

These third-party experts include:

  • eCogra (eCommerce Online Gaming Regulation and Assurance): A London-based agency that uses experienced experts to test and check if everything in a slot works as it should, including the RNG algorithm.
  • BMM Testlabs: An independent laboratory with over 30 years of experience in the field.
  • Gaming Labs International (GLI): A world-class testing facility that works with the global gaming industry. Their clients include gaming regulators, suppliers, and operators. 
  • iTech Labs: These are a world-leading testing and certification laboratory for Online Gaming systems, operating since 2004.

These third-party experts have been approved and are used by regulatory bodies. For example, in the UK, the United Kingdom Gambling Commission (UKGC) decides how the games RNGs are tested and which third company to use for these tests.

Do slots have a memory?

The short answer is no. The RNG algorithm creates each spin independently of previous outcomes.

Therefore, an online slot doesn’t have a memory and won’t produce a specific outcome, even if it wanted to. 

What is the correlation between RNG, Hit Rates, and RTP?

An online slot is built upon many fixed components based on billions of spins.

These include:

  • The max win or max win cap
  • The max win probability
  • Bonus game frequency
  • The volatility level
  • Return To Player (RTP) percentages
  • Hit Rates

The Random Number Generation algorithm then works based on the overall mathematics of the game combined with these settings. 

In the long run, the slot will produce the previously decided Return To Player (RTP) percentage, and it will land wins according to the decided Hit Rate Frequencies and the other factors based on billions of spins.

Any individual spin is still wholly random, thanks to the RNG software, which ensures that the outcomes generated are random and without bias.

Can you predict the outcome when playing slots?

It is not possible to find patterns or predict outcomes when playing online slots, as the Random Number Generator algorithm is created to prevent this from happening.

Any single spin is completely based on luck, and there are no skills involved that can influence the outcome in one way or another.

Hot and cold slots


Most of us who have played online slots for some time have probably experienced the hot or cold slots feeling.

However, this is nothing more than a feeling, as there is no such thing as a hot or cold slot, and each individual spin is entirely random, thanks to the RNG software.

Although unlikely, you could hit a win 20 spins in a row or go without any wins for the next 50 spins.

Still, in the end, the Hit Frequency guides how often, on average, you should hit a win in the long run.

Due to the Random Number Generators algorithm, there is no such thing as hot or cold slots; the next spin is completely random, regardless of the previous outcomes. It may feel like new slots are often “hotter” than older slots, but this is not true. New online slots are tried out by more players, which inevitably leads to more wins at the beginning of a slots’ life cycle.

It’s all about luck and nothing else.

Can you trust the Random Number Generator?

You can trust the Random Number Generator software 100% when playing slots on top-rated online casinos that have been approved with some of the most respected gambling licenses.

These online casinos only use games from the most popular game studios, and these slots have gone through rigorous tests by licensed third-party laboratories and agencies where qualified experts have tested the games and approved them.

Can casinos change the RNG?

Online casinos don’t have access to or any possibility of changing the Random Number Generator algorithm, so they can’t change the RNG in one way or another.

The game studios store the RNG algorithm on a remote gaming server and cannot be influenced.

Regulators constantly make regular checks to ensure that everything is up to date and no changes have been made to a game’s approved settings and RNGs. 

Volatility and RNG

Online slots are created with different volatility settings ranging from low, medium, and high.

The higher the volatility setting, the riskier the slot as you hit low to medium-sized wins less frequently, as the amounts are saved for a few more significant wins.

Conversely, on average, a low volatile slot will pay out more small/medium-sized wins, but the max win caps are lower to compensate for those wins.

The Random Number Generator algorithm takes the volatility, the game’s mathematics, and other settings into effect. However, each spin is still completely random, and it’s impossible to predict any future outcomes as it’s all based on pure luck.

Online Casinos with certified RNG slots

Frequently Asked Questions about RNGs:

What is RNG in slots?

The Random Number Generator (RNG) is a software where the algorithm ensures that the outcome of each spin is entirely random no matter what the results of previous spins have shown. This is the backbone of the online casino industry and guarantees that each licensed and approved slot delivers a fair outcome based on pure luck.

Is RNG in slots important?

Without the Random Number Generator (RNG) algorithm, online casinos couldn’t offer players a secure and fair gambling experience.

Who determines the RNG in online slots?

The Random Number Generator (RNG) software is created by game developers and approved by licensed third-party agencies and laboratories before being offered to players in online casinos.

Can I trust the RNG in slots?

Yes, when playing on licensed online casinos, you can rest assured that the licensees have appropriately tested and approved each game.

Are there any patterns in RNG?

No, RNG has no patterns, as the Random Number Generator algorithm guarantees each spin to be completely random, regardless of the previous outcomes.

Can you manipulate the RNG?

The Random Number Generator (RNG) formulas are stored in the game files on a gaming server hosted by the game developer or a third party and are not accessible once there. The RNG can, therefore, not be changed or manipulated as regulators make constant checks to ensure that everything is up to date.

Can online casinos change the RNG?

No, online casinos can’t change or influence the RNGs on slots as they have no access to the algorithm stored on external servers.

Do jackpots use an RNG?

Yes, the outcomes on jackpot slots are completely random, as these games also use a Random Number Generator (RNG) software that ensures that each spin is unplanned. Therefore, Jackpot wins on slots are wholly based on luck, and no skills or other methods are involved.

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