Random number generator (RNG): what it means in slots
A random number generator is the software that decides every slot outcome the instant you press spin.
By Ryan Jessop. Updated .
Key takeaways
- Decides each result at the press.
- Independent of previous spins.
- Tested by approved test houses for UK games.
- The basis of fair play, not of winning.
How it works
The RNG produces numbers continuously. When you press spin, the current number maps to a reel position. The animation simply shows a result already decided.
Testing in the UK
Gambling Commission technical standards require games and RNGs to be tested by approved independent test houses before release.
What it rules out
- Slots are never “due”.
- Stopping the reels early cannot change the result, and slam-stop is banned in the UK anyway.
- Time of day does not matter.
See are online slots rigged? and slot myths.
Back to: the full slot and spins glossary.
Slot figures are developers' published defaults, each confirmed against two sources; your casino may run a lower RTP. Offer terms dated 9 October 2026. How we check. 18+. Free help: 0808 8020 133 or safer gambling.
Frequently asked questions
Is an RNG truly random?
It produces statistically random results, tested before release.
Can a casino control the RNG?
Not at licensed casinos; games are tested and certified.
Does the RNG remember past spins?
No. Each spin is independent.