Every commercial gambling game is designed so that, over enough play, the operator keeps a predictable slice of the money wagered. That slice is called the house edge. It is not a secret or a trick: it is a simple consequence of how payouts are set. Understanding it is the single most useful piece of maths a player, parent or journalist can learn about gambling.
What the house edge actually is
The house edge is the average percentage of each stake that the operator expects to keep over the long run. If a game has a 2% house edge, then for every £100 wagered the operator expects, on average, to keep £2 and return £98 to players as winnings.
Two words in that definition matter:
- Average — the edge says nothing reliable about one spin, one hand or one evening. It describes the centre of a very wide spread of possible outcomes.
- Wagered — the edge applies to total turnover, not to the money you arrived with. If you deposit £50 and recycle your winnings until you have staked £500 in total, the edge applies to the £500.
Where the edge comes from
Casinos do not need to rig games to make money. They simply pay winning bets at slightly less than the “true” odds of the event.
Worked example: European roulette
A European wheel has 37 pockets: 1 to 36 plus a single zero. A bet on one number has a 1 in 37 chance of winning. A fair payout would therefore be 36 to 1 (you would get your stake back plus 36 units, matching the 36 losing pockets). The casino pays 35 to 1.
Imagine you bet £1 on each of the 37 pockets in one spin:
- You stake £37 in total.
- One bet wins and returns £36 (£35 winnings plus the £1 stake).
- You are left £1 down, every time.
£1 lost out of £37 staked is 1/37, which is 2.70%. That is the house edge on almost every bet on a European wheel.
American roulette
An American wheel adds a double-zero pocket, giving 38 pockets, but keeps the same 35 to 1 payout. Bet £1 on every pocket and you stake £38 to get £36 back: a loss of 2/38, or 5.26%. One extra pocket nearly doubles the cost of play. The “five-number” bet on 0, 00, 1, 2 and 3 is worse still at 7.89%.
Some French-rules tables apply la partage or en prison, which returns half of an even-money stake when zero lands. That halves the edge on those particular bets to 1.35%.
Typical house edges compared
Figures below are standard long-run values under common rules. Actual rules vary by table and operator, and the edge shifts with them.
| Game / bet | Typical house edge |
|---|---|
| Blackjack, perfect basic strategy | roughly 0.5%–1% (much higher with poor play) |
| Baccarat, banker bet (5% commission) | 1.06% |
| Baccarat, player bet | 1.24% |
| Baccarat, tie bet paying 8 to 1 | 14.36% |
| Craps, pass line | 1.41% |
| European roulette | 2.70% |
| American roulette | 5.26% |
| Online slots | commonly 2%–10% (RTP 90%–98%), set per game |
| National lotteries | often 40%–50% or more, as a large share funds good causes and tax |
Low-edge games are not “safe”: a low edge on a very fast game can still produce a high hourly cost.
Turning the edge into money: expected loss
The formula every player should know is:
Expected loss = stake per bet × house edge × number of bets
Example 1: a roulette evening
You bet £10 per spin on a European wheel, at around 40 spins an hour, for three hours.
- Number of bets: 40 × 3 = 120
- Total staked (turnover): 120 × £10 = £1,200
- Expected loss: £1,200 × 2.70% ≈ £32.40
Example 2: online slots
You play £1 spins on a slot with a 96% RTP (4% edge). Online slots can run at several hundred spins an hour; in Great Britain the regulator requires at least 2.5 seconds per spin, which still allows well over 1,000 spins an hour in principle. Take a moderate 600 spins an hour:
- Turnover per hour: 600 × £1 = £600
- Expected loss per hour: £600 × 4% = £24
- Over a two-hour session, five nights a week: roughly £240 a week, or more than £12,000 a year
That is the core lesson: the speed of a game multiplies the edge. You can run your own figures with our house edge calculator or estimate a year of play with the cost of play calculator.
Why the edge always wins in the end: variance and the law of large numbers
In a short session, luck dominates. In a long one, the edge dominates. Take even-money bets (red or black) at £10 a time on a European wheel, where each bet wins 18 times out of 37:
| Number of bets | Expected loss | Chance of finishing ahead |
|---|---|---|
| 10 | £2.70 | about 34% |
| 100 | £27 | about 36% |
| 1,000 | £270 | about 19% |
| 10,000 | £2,703 | about 0.3% |
The expected loss grows in a straight line with the number of bets. The spread of outcomes grows only with the square root of the number of bets. Over time the steady drag of the edge overwhelms the randomness, which is why frequent players almost always end up behind.
What does not change the edge
- Staking systems. Doubling after losses (Martingale) or any other progression changes the shape of your results, not the average. Every individual bet still carries the same edge, so total expected loss is still turnover × edge.
- Timing. A game with a certified random number generator has no memory. The time of day, a recent jackpot or a run of losses does not make it “due”.
- Mixing bets. Combining several negative-expectation bets cannot produce a positive one.
The genuine exceptions are narrow: games involving skill, such as blackjack with correct strategy or poker against other players (where the operator takes a fee, called the rake, instead of holding an edge). Even then, most players do not play well enough to overcome the built-in cost.
Using the edge as a budgeting tool
Seen properly, the house edge is a price. If you choose to gamble for entertainment, you can treat the expected loss as what that entertainment costs, decide whether it is worth it, and set firm limits. Our guide to setting deposit, loss and time limits explains how. If the numbers above feel uncomfortably familiar, or if you find yourself chasing losses, the support directory lists free, confidential helplines by country.
Frequently asked questions
What is the house edge on European roulette?
It is 2.70%. There are 37 pockets but a winning single-number bet pays 35 to 1 instead of the fair 36 to 1, which works out to an average loss of 1/37 of every stake.
Why is American roulette worse for the player?
The extra double-zero pocket means 38 pockets with the same payouts, so the edge rises to 2/38, or 5.26%, nearly double the European wheel.
Can I win if the house has an edge?
Yes, in the short run. Variance means individual sessions can end in profit, but the more you play, the more closely your results tend towards the expected loss.
Is the house edge the same as the RTP?
They are two sides of one number. A game with a 96% return to player has a 4% house edge.
Important: This article is general information, not legal, financial or medical advice. Rules change — always confirm with the relevant regulator. If gambling is causing you harm, free support is available.
