RNG stands for random number generator, the software that decides the result of every spin, card and dice roll in a digital casino game. In Britain, the Gambling Commission requires RNGs to be acceptably random and independently tested before a game goes live. An RNG can't be timed, read or worn down, and it doesn't owe you a win.
An RNG picks each result of a digital casino game at random.
UK rules require RNGs to be tested before games and RNGs are released.
Every result is independent: past spins don't make a win more or less likely.
Games can't fake near-misses or adjust their odds to make up for past results.
Live dealer games use real wheels and cards; RNG games use software.
Stands for
Random number generator
Used in
Slots, digital table games, First Person games
UK standard
RTS 7, generation of random outcomes
Testing
Before release, by approved test houses
Can it be predicted?
Should be computationally infeasible
What an RNG is
A random number generator is a piece of software, or sometimes a physical device, that produces numbers with no pattern you can use. A casino game maps those numbers onto outcomes: a reel stop, a playing card, a roulette pocket. Every spin of a slot in a casino app starts with an RNG call.
The term appears across our casino app glossary because it underpins so much else. The RTP of a slot, its volatility and the house edge of a digital table game are all long-run properties of how the RNG's numbers are mapped to prizes.
How an RNG decides a result
Think of a slot reel strip with many positions. When you press spin, the game asks the RNG for a number, scales it to the number of positions on each reel, and stops each reel at the matching symbol. The animation you see afterwards is a presentation of a result that has already been chosen.
For digital games that copy a physical device, the maths has to match the real thing. The Commission's guidance under RTS 7 on random outcomes (opens in a new tab) says a simulated wheel, dice or deck should have the same probabilities as the physical version. So a digital single-zero roulette wheel gives red a chance of 18 in 37 on every spin, about 48.6%.
Digital blackjack works the same way: an RNG-dealt game effectively reshuffles every hand, which is one reason card counting has no place in online RNG blackjack. More on how these games play on a phone is on our RNG casino games page.
RNG rules and testing in the UK
The Gambling Commission's technical standards set out what an RNG must do, and its testing strategy sets out how that's checked. The main points:
What UK rules require of RNGs and games
Requirement
What it means for you
Acceptably random (RTS 7A)
Output must pass generally accepted statistical tests for randomness
Unpredictable
It should be computationally infeasible to predict the next number
No compensation (RTS 7A)
A game can't change its odds to make up for earlier wins or losses
Fair mapping (RTS 7B)
Numbers are turned into results using the published pay tables, in the order received
No fake near-misses (RTS 7C)
A losing result can't be swapped for a near-miss losing result
Tested before release
New games and RNGs go live only after testing and a report to the Commission
Because each result is independent, nothing that happened before changes the next spin. The chance of red after five blacks in a row is still 18 in 37. The belief that a result is overdue is known as the gambler's fallacy, and UK rules specifically ban games that compensate for past results.
The maths of streaks works the same way. Two reds in a row on a single-zero wheel is (18/37) × (18/37), about 23.7%, but once the first red has landed, the second is back to 48.6% on its own. Over a long run, results drift towards the expected averages in proportion, not by paying back earlier shortfalls.
No timing, pattern or betting system changes what an RNG produces. The house edge applies to every bet, so losses are likely over time. Our answer on whether casino apps rig games explains what licensing does and doesn't promise.
RNG games vs live dealer games
Not every casino game uses an RNG for its main result. In a live dealer game a real wheel spins or real cards are dealt on camera, and optical character recognition turns the physical result into data the software can use. Evolution's First Person games, by contrast, are RNG games presented in 3D animation: the deal, spin or roll is decided by software.
RNG and live games compared
Point
RNG game
Live dealer game
What decides the result
Software random number generator
Physical wheel, cards or dice
How you see it
Animation
Video stream
UK minimum game cycle
2.5 seconds for slots; 5 seconds for other casino games
5 seconds for casino games
Data use
Lower, mostly graphics and small result messages
Higher, continuous video
Both kinds are covered by the same UK speed rules and autoplay ban. See live casino apps for the video side.
Related terms
RTS: the Remote Technical Standards that include the RNG rules.
Game cycle: one complete round, from stake to result.
Paytable: the prize list the RNG's results are mapped to.
Demo mode: play-money versions, which in Britain still need age checks.
RNG slots in our partner casino apps
All UK-licensed apps work under the same RNG rules, so randomness isn't a point of difference between brands. Where they differ is in their welcome offers, which apply to slots. Each is 18+, for new customers, with terms applying.
Coral: from 1 October 2026 to 1 February 2027, deposit (some types excluded) and bet £10 on slots to receive 100 free spins on selected games. Each spin is worth 10p; accept within 48 hours, then 7 days to use them. No wagering applies to winnings from the spins.
Ladbrokes: play £10 or more on slots after depositing and you get 50 free spins a day for the first 10 days, up to 500, valued at 10p on selected games. Claim by 23:59 each day; spins last 7 days and carry no wagering.
PlayOJO: 80 free spins on Big Bass Bonanza at 10p each for new UK customers (not Northern Ireland) who deposit at least £10 the first time. No wagering, winnings paid in cash, not combinable, designated link only.
Coral and Ladbrokes are both operated by LC International Limited (Entain), so you may only be able to open a new account with one. For a broader comparison, see best slot apps.
Coral and Ladbrokes are both run by LC International Limited (Entain). If you already hold an account with one Entain brand, you may not be able to open another; check the terms first.
Significant terms: 18+. New players only. Offer runs 01/10/2026 to 01/02/2027. Deposit (certain types excluded) and bet £10+ on slot games to get 100 free spins (selected games, £0.10 each, 48 hrs to accept, valid 7 days). No wagering on free spin winnings. Deposits by Neteller, PayPal, Paysafe, Skrill, prepaid cards and certain debit cards do not qualify. Restrictions and T&Cs apply. GamCare.org.uk
Read our Coral app reviewLicence: LC International Limited, Gambling Commission account 54743. Offer checked 5 October 2026.
Time limitClaim daily for 10 days; each batch valid 7 days
Worked valueUp to 500 spins at £0.10 (up to £50 in spins)
Significant terms: 18+. New customers only, from 14/11/25 until further notice. Certain deposit methods excluded. Deposit and spend £10+ on slots for 50 free spins a day during the first 10 days after first deposit and registration (max 500, £0.10 each, selected games, claim before 23:59 each day, valid 7 days). No wagering. Prepaid cards, PayPal, Paysafe, Neteller, Skrill and Moneybookers deposits do not qualify. Restrictions and T&Cs apply. GamCare.org.uk
Read our Ladbrokes app reviewLicence: LC International Limited, Gambling Commission account 54743. Offer checked 5 October 2026.
Significant terms: 18+. New UK customers (excluding Northern Ireland). First deposit only. Minimum deposit £10. 80 free spins on Big Bass Bonanza, £0.10 each. No wagering requirements; winnings paid in cash. Cannot be used with any other offer. Only available to players who arrive through the designated offer link. Full T&Cs apply. GamCare.org.uk
Read our PlayOJO app reviewLicence: Skill On Net Limited, Gambling Commission account 39326. Offer checked 5 October 2026.
18+. Every casino game has a built-in house edge, so over time you should expect to lose what you stake. Set a budget before you play and stop when it’s gone: safer gambling tools and support. Free, confidential help: National Gambling Helpline 0808 8020 133.
Frequently asked questions
What does RNG mean in a casino app?
RNG means random number generator, the software that decides each result in a digital casino game, from slot spins to cards in RNG blackjack. The animation you see shows a result already chosen. UK-licensed games must use RNGs that pass statistical tests for randomness and are checked before release. Our page on RNG casino games on mobile explains which games use one and how they play on a phone.
Can you predict or beat a casino RNG?
No. The Gambling Commission's guidance says it should be computationally infeasible to predict the next number, and games can't adjust their odds based on past results. Timing your taps, watching patterns or changing stakes doesn't alter the outcome. Every bet carries the game's house edge, so losses are likely over time. Our house edge entry shows how that cost works out in pounds.
Are RNG games tested in the UK?
Yes. Under the Commission's testing strategy, new games and RNGs can only be released once testing is complete and a report has been provided to the Commission. Testing includes source code review and statistical analysis of raw RNG output, and the Commission publishes a list of approved test houses. Our guide to how casino apps are licensed in the UK puts this in context.
Is a slot due a win after a long losing run?
No. Each spin is independent, so a long run of losses doesn't make the next spin more likely to pay. UK rules ban compensated games, meaning a game can't change its odds to balance earlier results. Believing a win is overdue is the gambler's fallacy. If you find yourself chasing losses, our page on signs of problem gambling and the National Gambling Helpline on 0808 8020 133 can help.
Do live casino games use an RNG?
Not for the main result. Live dealer games use a real wheel, cards or dice filmed in a studio, with the physical result read into the software. Some live game shows add random multipliers or bonus rounds generated by software, and RNG versions of live titles exist, such as Evolution's First Person range. Our game show entry explains how those formats mix the two.
Is the RNG different in the app and on the website?
The randomness rules are the same wherever you play with a UK-licensed operator, because they apply to the game, not the device. What can differ between operators is the RTP version of a game, which changes the long-run return but not the randomness of each result. Check the game's help screen in the app. Our answer on whether RTP is lower on casino apps covers this.
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