What Is a Random Number Generator?
This is an independent, informational guide for UK readers and is not affiliated with the organisations mentioned. It is provided for general information only.
A random number generator, or RNG, is software that produces unpredictable results — the digital equivalent of shuffling cards or drawing balls. It decides the outcome of online slots, bingo and instant-win games, and on licensed UK sites it's independently tested for fairness.
Software that produces random results
A random number generator, or RNG, is software that produces unpredictable results — the digital equivalent of shuffling cards or drawing balls. It's what decides the outcome of online slots, bingo and instant-win games.
Each result is independent of the last, so the software has no memory of previous spins or games.
How RNGs are kept fair
On licensed UK sites, the RNG is tested by independent laboratories to confirm its results are genuinely random and match the game's stated odds. Operators must use tested games as a condition of their licence.
That independent testing is what lets players trust an online result they can't physically see being drawn.
Where RNGs are (and aren't) used
RNGs power online casino and bingo games and digital instant-win games. The National Lottery's main draws, by contrast, use physical ball machines, drawn under supervision, rather than software.
Either way, the goal is the same: a result no one can predict or influence.
Why you can trust a tested RNG
Because you can't watch an online result being drawn, independent testing is what stands in for that transparency — a lab confirms the RNG behaves randomly over millions of trials.
A licensed operator displaying its credentials is the sign that this testing has been done.
Understanding the RNG is the key to understanding online fairness: results you can't watch being drawn are kept honest by independent testing rather than blind trust. When a licensed site shows it uses tested games, that's your assurance the digital 'draw' is as fair as a physical one.
What does a random number generator do?
It produces unpredictable, independent results that decide the outcome of online slots, bingo and instant-win games.
Are random number generators fair?
On licensed UK sites they're independently tested to confirm results are genuinely random and match the stated odds.
Does the National Lottery draw use an RNG?
The main draws use physical ball machines under supervision; RNGs are used for online instant-win games.
How can an RNG be checked if I can't see it?
Independent test labs run millions of trials to confirm it behaves randomly and matches the stated odds, as a licence condition.
Related guides: Are online bingo sites fair?, Is the lottery rigged?, Responsible gambling
18+ only. Gambling should be fun, not a way to make money. If you are worried about your gambling, or affected by someone else's, free and confidential help is available from the National Gambling Helpline on 0808 8020 133, from BeGambleAware.org, and through the self-exclusion scheme GAMSTOP. You must be 18 or over to gamble.