House edge is the percentage of total stakes that a casino game is mathematically designed to retain on average over a very large number of plays, under the stated rules and any assumed strategy. Return to player, or RTP, describes the complementary share expected to be returned when both figures use the same basis: a 2.5% house edge corresponds to 97.5% theoretical RTP. Neither percentage predicts what will happen in one short session. This guide is for adults aged 18 and over.
What the house edge actually measures
The house edge is a long-run mathematical rate, not a fee removed in equal slices from every stake. A 2.5% edge does not mean every £100 sequence must lose exactly £2.50. It means that, across a sufficiently large body of equivalent play, the game’s rules imply an average advantage of 2.5% of turnover for the house. A person can finish a particular sequence ahead, behind or close to even without changing that underlying calculation.
The figure depends on the exact game and bet. In a game where decisions affect the result, it can also depend on the strategy assumed in the calculation. Check the rules or help screen rather than transferring a percentage from a different version of a game. Under Great Britain’s remote technical standards, relevant information about house edge, RTP or winning probability must be easily available before a customer commits to play.
How to calculate theoretical expected loss
- Find total turnover: stake per round × number of rounds.
- Convert the published house edge from a percentage to a decimal.
- Calculate theoretical expected loss: turnover × house edge.
Turnover is the total amount staked across all rounds. It is not the same as a deposit or starting balance because the same money can be staked again after a return. The calculation describes a theoretical average across repeated equivalent play; it is not a bill, a target or a forecast for one person’s session.
House edge versus RTP
- House edge expresses the game’s theoretical long-run retained share of turnover.
- RTP expresses the theoretical long-run returned share of turnover.
- The two add to 100% only when they refer to the same game, rules, eligible outcomes and strategy assumptions.
- Neither percentage is the probability of finishing a session in profit.
Why a short session can look completely different
Game outcomes vary around their theoretical average. The Gambling Commission describes RTP as an average measured over a large number of games and says a typical session will vary because of normal volatility. Its monitoring guidance also uses wider tolerance ranges when only a limited amount of play has been measured and narrower ranges as the volume grows. A run above or below the stated RTP therefore does not show that a game is ‘due’ to correct itself on the next round.
A practical decision rule
- Use the published house edge or RTP to understand long-run mathematical cost, not to predict a session.
- Confirm that the percentage applies to the exact rules and bet being considered.
- For games involving decisions, check which strategy the percentage assumes.
- Base any expected-loss calculation on total turnover, not only the opening balance.
- Do not treat a lower edge as a promise of profit or as evidence that a particular session is safe.
- If the relevant rules and probability information are not accessible, pause rather than guessing.
- Never increase stakes or continue solely because recent results appear to be ‘due’ to reverse.
If gambling feels difficult to control or is affecting your finances, relationships or wellbeing, stop and use the protected Help route for neutral support information.