NewsSlot DesignSlot MechanicsUK Gambling Commission
How do online slots work? RNG, RTP and the UK rules
An RNG produces the result, the paytable maps it to the reels, and in Great Britain the UKGC's technical standards govern pace, stakes and display.
By Staff, Spin & Tell
Online slots work by drawing a number from a random number generator for each spin, then mapping that number to reel positions through the game’s paytable. The reels then present that result. RTP and volatility describe the game’s long-run maths, not the next spin.
This is an evergreen explainer. Its rules are Great Britain’s, under the UK Gambling Commission’s Remote Gambling and Software Technical Standards; other markets set their own. This desk read the Commission’s RTS 7 and RTS 14 pages, its stake-limit guidance and its auto-play consultation response on 15 October 2026.
How do online slots work under the UK rules?
| Rule | What it requires |
|---|---|
| RTS 7A | RNG output and results “acceptably random”; no compensated game |
| RTS 7B | Numbers mapped to outcomes per the paytable, used in the order received |
| RTS 7C | No substituting a losing result with a near-miss losing result |
| RTS 8C | Each game cycle committed individually; no auto-play on slots, in force since 31 October 2021 |
| RTS 14C | No playing multiple games at once; split and multi-screen named |
| RTS 14D | At least 2.5 seconds per slot game cycle; start button released and pressed again |
| RTS 14E | No reducing the time to the result; turbo, quick spin and slam stop not permitted |
| RTS 14F | No celebrating a return equal to or below the total stake |
| Stake limit | £5 per game cycle at 25 and over (from 9 April 2025), £2 for 18 to 24 (from 21 May 2025) |
The RTS 14 page carries the pacing and display rules. The stake-limit guidance ties the caps to a 2025 statutory instrument attached to remote casino operating licences. None of the four ranking explainers read at the search stage cites these requirements; in the text read, Racing Post’s presents autoplay as a player option.
How does the RNG work in online slots?
The RTS 7 guidance asks for output that is uniformly distributed, does not repeat a stream, and cannot feasibly be predicted without the algorithm and seed. Scaling the numbers to a reel strip must keep those qualities.
RTP, volatility and the paytable
RTP is the share of stakes a game is designed to return over a very long run; volatility is how unevenly it does so. The same title can carry more than one RTP figure: this site’s Gremlins After Midnight RTP post found a third-party sheet printing three, and its max win post found four coverage sheets that all print N/A for the cap while disagreeing on RTP. The site’s Hold and Spin explainer covers one bonus mechanic built on top. The paytable inside the build you load is the copy of record.
Online slots questions
Are online slots random?
In Great Britain they must be. RTS 7A requires random number generation and game results to be acceptably random, demonstrable through statistical testing, and forbids a compensated game that adjusts its odds during play. Random does not mean even: the paytable sets the probabilities, and RTP describes a long-run average across a very large number of spins, not the next one.
Do online slots have different RTP at different casinos?
One game can be listed at more than one RTP figure. This site’s look at Gremlins After Midnight found a third-party sheet printing three. None of the sources read for this piece says which build a given site runs, so the RTP shown in the paytable of the game you load is the figure that applies.
How does the RNG work in online slots?
The RNG outputs numbers that should be uniformly distributed and, for a software generator, computationally infeasible to predict without the algorithm and seed. The game scales those numbers and maps them to reel positions under its paytable. Under RTS 7B the numbers are used in the order received and may not be discarded to steer a result.
This describes how a game is built and regulated, not how to play one; nothing here was played or recommended. 18+. Every slot carries a built-in edge, and the paytable governs every session.