How online casinos work
Five parts: an operator, game studios, a random number generator, a cashier and a regulator.
By Ryan Jessop. Last checked .
Key takeaways
- The casino is a shop; studios make the games.
- Results come from a tested random number generator.
- The casino earns the house edge.
- The Gambling Commission is its regulator.
Quick answerAn online casino is a licensed operator that hosts games made by separate studios. A random number generator decides each result, the casino keeps a small share of stakes called the house edge, and the Gambling Commission regulates it.
The five parts
| Part | Job |
|---|---|
| Operator | Runs the site, holds your account and the licence |
| Game studios | Make the slots and tables; licensed separately |
| Random number generator | Decides each result; tested by a laboratory |
| Cashier and payment firms | Move money in and out |
| Gambling Commission | Issues licences and polices all of it |
What happens when you press spin
Your stake leaves your balance. The game asks its random number generator for a number, and that number fixes where the reels stop before they have finished moving on your screen. The animation is for show. Any win is added to your balance and the round is recorded on the studio's server.
How the casino earns its income
Not by fixing games, which would cost it the licence, but through the house edge: over millions of rounds a 96% slot pays back 96p in the pound and keeps 4p. Individual players win and lose around that average.
Live games are different
A live table uses real cards and wheels, filmed in a studio. There is no random number generator; the result is whatever physically happens.
Offer terms were read from each casino's published conditions and dated 5 October 2026. Game rules and house edges are standard published figures. Casino details other than offers come from independent reviews; we have not opened real-money accounts. How we check. 18+. Free help: 0808 8020 133 or safer gambling.
Frequently asked questions
How do online casinos work?
A licensed operator hosts tested games and keeps a small house edge.
Who decides the result?
A random number generator, or real equipment at live tables.
How do casinos earn their income?
From the house edge.
Who regulates them?
The Gambling Commission.