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How do online casinos work?
Short answer: every game has a built-in house edge, so the casino keeps a small percentage of everything bet over time. RTP tells you how much a game pays back on average, but in any one session anything can happen.
Online casinos are businesses built on simple maths. Every game is designed so the casino keeps a small slice of everything bet over time. Understanding that slice is the best protection you have as a player.
1. The house edge
The house edge is the percentage of every bet the casino expects to keep in the long run. It's built into the rules and payouts of every game, so it's always there, no matter how lucky a session feels.
| Game | Typical house edge | What that means |
|---|---|---|
| Blackjack (basic strategy) | About 0.5% | Among the lowest, but only if you play the maths-correct moves |
| Baccarat (banker bet) | About 1.06% | Low edge and simple to play |
| European roulette (single zero) | About 2.7% | The single green zero is the casino's edge |
| Online slots | About 2% to 6% | Depends on the game's RTP, often 94% to 98% |
| American roulette (double zero) | About 5.26% | The extra zero nearly doubles the edge |
2. RTP: return to player
RTP is the flip side of the house edge. A slot with 96% RTP is designed to pay back $96 of every $100 bet, averaged over millions of spins across all players. It doesn't mean you'll get $96 back from your $100 tonight. In a single session you might win big or lose the lot.
Many casinos let you check a game's RTP in its info or help screen. Higher is better for you, and some casinos run lower RTP versions of popular slots, so it's worth a look.
3. Volatility: how bumpy the ride is
- Low volatility games pay small wins often. Your balance moves slowly.
- High volatility games go quiet for long stretches, then occasionally pay big. Your balance can drop fast.
Two slots with the same RTP can feel completely different because of volatility.
4. Random number generators
Slots and digital table games use a random number generator (RNG) to decide every result. Each spin is independent, so a machine is never "due" a win, and a big win doesn't make the next spin any less likely to pay. Reputable casinos use games from studios whose RNGs are tested by independent labs.
5. Live casino
Live dealer games stream real dealers, cards and wheels from a studio. The results come from the physical game rather than an RNG, but the house edge works exactly the same way.
6. Bonuses are marketing
A bonus is the casino paying to win you as a customer. The wagering requirement makes sure that you bet enough for the house edge to win most of it back. Our wagering calculator shows what any bonus really costs.
7. How review sites like Spinafil get paid
Most casino review sites, Spinafil included, earn affiliate commission when a player signs up through their link. Often that's a share of what the casino makes from that player. We're upfront about it because it's exactly why you should judge any review site by how honest it is about payouts and catches, not by how big its bonuses look. Read our affiliate disclosure.
What it all means for you
- Over time, the house always comes out ahead. Treat gambling as paid entertainment, not a way to make money.
- Set a budget before you play and stick to it.
- Pick games with higher RTP and casinos that actually pay out. That's what our rankings are about.
- If it stops being fun, stop. Free help is on our Keep it fun page.
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