Two ways of describing the same thing: the built-in mathematical advantage the operator has over time.
Return to player (RTP)
RTP is the percentage of all money wagered on a game that it is designed to pay back to players over the very long run. A slot with 96% RTP is expected to return about £96 for every £100 wagered across millions of spins — not within your session. Short sessions swing widely in both directions; RTP is a long-run average, not a promise.
House edge
The house edge is simply the other side of RTP: house edge = 100% − RTP. A 96% RTP game has a 4% house edge. This is the operator’s expected margin over time and is how casino games are designed to be profitable.
Why the long run matters
Because outcomes are random and independent, anything can happen in a single session — that’s why people sometimes win. But the more you play, the closer your results tend to move toward the game’s RTP, which is below 100%. There is no strategy that changes a slot’s RTP.
Comparing games
Higher RTP means a smaller expected cost to play, all else being equal. Table games like blackjack can have very low house edges with correct play, while some slots and side bets carry much higher edges. Always check the game’s stated RTP where it’s published.