The house edge is the percentage of each bet a casino expects to retain over the long run. It's built into the rules of every game before a single card is dealt or a reel is spun. A house edge of 5% doesn't mean you lose 5 cents on every dollar right away. It means the casino expects to keep 5% of all the money wagered across thousands or millions of rounds. For the individual player on a single session, anything can happen. Over time, the math wins.
How the house edge works
Every casino game pays out at odds that are slightly worse than the true probability of winning. That gap is the house edge. In American roulette, there are 38 pockets on the wheel (1 through 36, plus 0 and 00), but a straight-up bet pays only 35-to-1. The true odds of hitting any single number are 37-to-1. The difference between those two figures produces a house edge of 5.26%. The casino collects that margin on every spin, from every player, forever.
Blackjack works differently. The house edge in blackjack comes primarily from one rule: the player busts first. If you draw to 22 and then the dealer also draws to 22, you've already lost. Basic strategy reduces blackjack's house edge to around 0.5% at most standard tables, making it one of the lowest in the casino. Slot machines sit at the other end of the scale, with house edges that typically run between 2% and 15% depending on the game and the operator.
The house edge is closely related to RTP (return to player), which is simply its mirror image. An RTP of 96% means a house edge of 4%. The two figures describe the same mathematical relationship from opposite directions: RTP tells you what comes back to players, and the house edge tells you what stays with the casino.
House edge vs hold percentage
Many people confuse the house edge with the hold percentage, but they measure different things. The house edge is a theoretical figure calculated from the game's rules. The hold percentage is an observed figure: the actual share of money exchanged for chips that the casino keeps at the end of a session. Hold percentages are almost always higher than the house edge, because players don't bet their buy-in once and leave. They recycle chips, re-bet winnings, and stay at the table. Every re-bet exposes those chips to the house edge again. A casino might hold 20% of a player's buy-in even on a game with a 1% house edge, simply because the player kept playing.
House edge by game type
The house edge varies enormously across game categories. Baccarat (banker bet) sits around 1.06%. European roulette runs at 2.7%, versus 5.26% for the American version. Craps, on the pass line, comes in at 1.41%. Table games consistently offer lower house edges than machine-based games, which is why casual players chasing entertainment often gravitate toward slots while those who care about expected loss per hour tend to stick to the felt.
Keno carries some of the highest house edges in any casino, regularly exceeding 25%. Slot machines are harder to pin down because operators can configure their return to player settings within regulatory limits, and those limits differ by jurisdiction. In markets regulated by the UK Gambling Commission, for instance, online slots must meet minimum RTP thresholds set by the regulator. The published RTP on any given slot converts directly to the game's house edge.
Why the house edge matters for real players
The house edge defines your expected cost of play. If you bet $10 per hand, play 60 hands an hour, and the game carries a 1% house edge, your theoretical loss rate is $6 per hour. That's not a guaranteed outcome for any single hour. It's a long-run average that becomes more reliable as the number of rounds increases. Short sessions can swing dramatically in either direction. Over tens of thousands of rounds, the actual results will converge toward the theoretical expectation.
Knowing the house edge also helps you evaluate bonuses. A deposit bonus always comes with a wagering requirement, and the house edge determines how much of that bonus money you're likely to lose while meeting it. A 40x wagering requirement on a $100 bonus means $4,000 in total bets. On a game with a 5% house edge, the expected cost of clearing that requirement is $200. You'd need to lose less than the bonus value for the promotion to be worth taking.
The house edge isn't a conspiracy or a trap. It's the casino's business model, disclosed (at least implicitly) in every game's rules. Players who understand it spend less time chasing losses and more time making deliberate choices about where and how they bet.
Can the house edge be overcome?
Card counting in blackjack shifts the edge toward the player under specific conditions, which is why casinos use multiple decks and reserve the right to ask counters to leave. Advantage play techniques exist for video poker too: certain game variants with full pay tables return over 100% with perfect strategy, meaning the player holds the edge. These opportunities are rare, usually small, and require significant skill and bankroll. For the vast majority of players, the house edge is a fixed cost of entertainment, not a problem to be solved.
The practical takeaway is simple: choose games with low house edges if your goal is to extend your playing time, and treat the house edge as the price you pay for the experience. It doesn't make gambling irrational. It makes it predictable, once you know where to look.