Return to player is quoted on every slot and understood by almost nobody, because the number describes something on a timescale nobody plays on. Here is the arithmetic, done out loud, using round figures so the shape is visible.
The calculation everybody has in mind
Take a slot advertised at 96% RTP. Stake £1 per spin, play 1,000 spins.
That is the calculation, and it is correct. It is also close to useless as a prediction of your evening, for one reason: it is an average over a number of spins far larger than 1,000, and the spread around that average is enormous.
The part the number hides
Two slots can both advertise 96% and behave nothing alike. A low-volatility game pays small amounts often, so a thousand spins lands somewhere reasonably near the average. A high-volatility game holds nearly all of its return in rare large outcomes, so a thousand spins on it most commonly ends well below the average, with a small chance of ending far above it.
Same RTP. Completely different distribution of what actually happens to you. The advertised percentage tells you where the centre is and says nothing about how far from the centre you are likely to land, which is the thing you experience. GambleDragon works through the definition properly in its explainer on what the RTP figure is averaged over, and the distribution side in its piece on reading a volatility rating.
Two corollaries worth holding on to
RTP does not accumulate towards you. A game that has paid badly is not owed. Each spin is independent, and the average is reached by there being a very large number of spins in the world, not by yours balancing out.
The cost scales with total stake, not with time. The expected cost of £1,000 staked is the same whether you stake it over an evening or a month. Which means the practical lever on cost is not which game you pick or how long you sit there; it is how much you put through. Everything else is a preference about what the session feels like.
Sources
- The arithmetic above is illustrative and uses round figures; it is not derived from any specific game's published data.
- UK Gambling Commission — player information on how games are tested, gamblingcommission.gov.uk (accessed 1 August 2026)
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