How Casino Games Work: House Edge, RTP and Why the House Wins in the Long Run

Casino games can feel like a contest between you and luck, but the rules of each game are built so the casino expects to earn a positive return from the edge over time. This guide explains the key ideas, which apply in every country. Whether you can play online depends on where you live, as we explain below.

What the house edge means

The house edge is the average percentage of each bet the casino expects to keep over time. If a game has a 2.7% house edge, the casino expects to keep £2.70 for every £100 staked, on average, across a very large number of bets.

It does not mean you lose £2.70 every time. In a single session you can win or lose far more. The edge only shows up reliably over thousands of bets, which is why casinos can rely on it.

Return to player

Return to player (RTP) is the opposite way of describing the same thing. An RTP of 97% means that, across many plays, the game pays back 97% of what is staked and keeps 3%. RTP is a long-term average calculated over millions of plays. It tells you nothing about what will happen in your session.

Typical house edges

These are approximate figures for common games.

• European roulette: 2.70% (one zero).
• American roulette: 5.26% (two zeros, mainly seen outside the UK).
• Blackjack: around 0.5% with correct basic strategy, but higher if you play by instinct.
• Baccarat: about 1.06% on the banker bet and 1.24% on the player bet; the tie bet is much worse.
• Slots: set by the operator and published as RTP, commonly somewhere in the mid-90% range online, meaning an edge of a few percent.

Our guides to roulette and blackjack odds and slots explained cover these games in more depth.

Random number generators and live dealers

Online casino games such as slots and virtual roulette use a random number generator (RNG) to decide outcomes. Licensed operators in regulated markets must have their games tested by independent laboratories to show results are random and the stated RTP is accurate. Live casino games use real dealers and physical equipment streamed to your device, but the same mathematical edge applies.

Why betting systems do not work

Systems such as doubling your bet after a loss (the Martingale) promise to recover losses. They cannot change the house edge, because every spin or hand is independent. Doubling quickly pushes your stake beyond table limits or your bankroll, so a short losing run can wipe you out. Past results do not affect future ones: a roulette wheel has no memory, and “due” numbers are a myth.

Bonuses and the edge

Casino bonuses often come with wagering requirements. Playing through them means placing bets that each carry the house edge, so the bonus may cost more than it is worth. Try the wagering calculator on our free spend tracker and calculators page and read how bonuses actually work.

Where online casino games are legal

• Great Britain: regulated by the UK Gambling Commission; minimum age 18.
• United States: real-money online casino exists in only a few states (including New Jersey, Pennsylvania, Michigan, West Virginia, Connecticut, Delaware and Rhode Island), usually for ages 21 and over. Most states do not allow it.
• Ireland: licensing is being rolled out under the Gambling Regulatory Authority of Ireland, starting with betting. Online casino licensing has not opened yet, so check the current position.
• Canada: Ontario has a regulated online casino market; other provinces differ and some run their own government sites. The age is 19 in most provinces.
• Australia: online casino games, including pokies and live dealer tables, cannot legally be offered to people in Australia.

Playing sensibly

• Set a budget before you start and treat it as the cost of entertainment.
• Remember that a lower edge lowers the expected cost of each pound staked, although stake size and speed of play also matter.
• Use deposit limits and reality checks, which operators licensed in Great Britain must offer.
• Stop if you are chasing losses.

A simple illustration

As an illustration, with invented figures, imagine staking £10 per spin on European roulette for 100 spins, which is £1,000 staked in total. At a 2.70% edge, the expected average loss is £27. Some sessions will end well ahead and others far behind, but if thousands of players did the same, the average result would settle close to a £27 loss each. This is exactly how the casino plans its income, and it is why the house does not need to cheat.

Choosing games with your budget in mind

How quickly a budget shrinks depends on the edge, the bet size and the speed of play together. For illustration, with invented figures, a £1 bet on a 5% edge game and a £10 bet on a 0.5% edge game both have an expected cost of 5p per bet. At 100 bets an hour, each costs about £5 an hour on average. A faster pace or a larger stake raises the hourly cost, and a lower edge reduces it. Our “how long will my money last” calculator on the free spend tracker and calculators page lets you try your own numbers.

The bottom line

Every casino game has a built-in house edge, shown as RTP when stated from the player’s side. The edge gives the operator a positive expected return across repeated play. Actual results vary, and a casino’s business profit also depends on its costs, but no betting system can change the edge. Enjoy casino games as entertainment, play only where they are legal and licensed for your location, and never play with money you cannot afford to lose.

Sources

• Gambling Commission: Remote gambling and software technical standards (gamblingcommission.gov.uk)
• Interactive Gambling Act 2001 (legislation.gov.au)
• Alcohol and Gaming Commission of Ontario: iGaming (agco.ca)
• eCOGRA: How RNG testing works (ecogra.org)
• Wizard of Odds: House edge of casino games (wizardofodds.com)

18+ only (21 in most US states, 19 in most Canadian provinces for casino and betting). Gambling can be addictive. Free, confidential help is available: Great Britain: England and Scotland 0808 8020 133, Wales 0808 2819 265 (free, 24 hours), and GAMSTOP (gamstop.co.uk); US: National Problem Gambling Helpline 1-800-MY-RESET (the older 1-800-522-4700 also works); Australia: Gambling Help Online 1800 858 858 and BetStop (betstop.gov.au); Ontario, Canada: ConnexOntario 1-866-531-2600; Ireland: speak to your GP or the HSE. Never gamble money you need for living costs.