How slot machines work

Eight parts of a slot machine, one page each.

Ryan JessopBy Ryan Jessop. Last checked .

Key takeaways

  • A random number generator decides every spin.
  • Reels show a result already chosen.
  • RTP is the long-run return.
  • Volatility is how it arrives.

In shortA slot machine picks a random number for each reel when you press spin, shows the matching symbols and pays whatever the paytable says. Everything else is presentation.

Eight parts

Part 1The random number generatorThe part of a slot machine that decides everything.Part 2Reels and symbolsWhat you see spinning, and what it means.Part 3Paylines and ways to winHow a machine decides whether symbols make a win.Part 4The paytableThe one screen that tells you what a machine pays.Part 5Return to playerThe share of stakes a machine pays back over its lifetime.Part 6VolatilityWhether a machine pays little and often, or seldom and large.Part 7Bonus featuresWhere most of a modern machine's excitement, and much of its return, sits.Part 8JackpotsThe top prize, and how it is funded.

Features and symbols

SectionFeaturesEleven mechanics, from holds to multipliers.SectionSymbolsCherry, bell, BAR, seven and gems.

Common questions

One spin, start to finish

  1. You set a stake and press spin.
  2. The random number generator supplies a number for each reel.
  3. Each number maps to a stop on that reel.
  4. The reels animate and stop.
  5. Wins are counted by lines, ways or clusters.
  6. Features trigger if their symbols landed.
  7. Your balance updates.

Go further: Pub slot machines, The lucky seven and Free slot machines.

Slot figures are developers' published defaults, each confirmed against two sources; the version at your casino can differ. UK land-based stake and prize limits and online rule dates were checked against Gambling Commission and licensing authority sources on 6 October 2026. History follows commonly cited accounts. Offer terms dated 5 October 2026. How we check. 18+. Free help: 0808 8020 133 or safer gambling.

Frequently asked questions

How do slot machines work?

A random number generator picks each result; the paytable sets what it pays.

Are they random?

Licensed machines are tested to be.

Can you tell when one will pay?

No.

Types of slot machineTypes of slot machine explained.The history of slot machinesThe history of slot machines.Seven slot machines, taken apartSeven popular online slot machines taken apart.

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