Two Numbers That Define Every Casino Game
Whether you're spinning a slot reel or sitting at a blackjack table, two numbers quietly govern your experience: Return to Player (RTP) and the house edge. Understanding what they mean — and how they relate to each other — is the single most important piece of foundational knowledge for any online casino player.
What Is RTP?
RTP stands for Return to Player. It's expressed as a percentage and represents the theoretical proportion of all wagered money that a game will pay back to players over a very large number of rounds.
For example, a slot machine with an RTP of 96% will, in theory, return £96 for every £100 wagered across millions of spins. The remaining £4 represents the casino's built-in profit margin.
Important: RTP Is a Long-Run Average
RTP does not mean you'll get back 96% of your money in a single session. It's calculated over hundreds of thousands or millions of game rounds. In any individual session, results can swing dramatically in either direction. This is why variance (also called volatility) matters — more on that below.
What Is the House Edge?
The house edge is simply the flip side of RTP:
House Edge = 100% − RTP
A game with a 96% RTP has a 4% house edge. This means the casino expects to retain 4% of all money wagered on that game over time. It's the mathematical advantage built into every casino product.
RTP and House Edge Across Common Games
| Game | Typical RTP | House Edge |
|---|---|---|
| Blackjack (basic strategy) | ~99.5% | ~0.5% |
| European Roulette | ~97.3% | ~2.7% |
| American Roulette | ~94.7% | ~5.3% |
| Baccarat (Banker bet) | ~98.9% | ~1.1% |
| Online Slots | 92%–97% (varies) | 3%–8% (varies) |
| Keno | ~75%–80% | ~20%–25% |
What Is Variance (Volatility)?
Variance describes how a game's payouts are distributed. Two games can share the same RTP but feel completely different to play:
- Low variance: Frequent small wins, slower bankroll depletion. Common in classic slots and even-money table bets.
- High variance: Rare but large wins, long dry spells. Common in progressive jackpot slots and multi-reel bonus games.
Choosing a volatility level that matches your bankroll and playing style is just as important as choosing a high-RTP game.
How to Use This Knowledge Practically
- Always check a slot's RTP before playing — reputable online casinos list this in the game's information panel.
- Favour games with lower house edges if you want your bankroll to last longer.
- Don't confuse RTP with a win guarantee — it describes statistical behaviour over millions of rounds, not your next session.
- Apply strategy in skill-based games like blackjack to get closer to the theoretical best RTP.
The Bottom Line
RTP and house edge are the foundation of informed casino play. They won't tell you what will happen in your next session, but they will tell you which games offer better long-term value for your money. Armed with this knowledge, you can make deliberate, rational decisions about where and how to play.