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Guide to Online Slots

Ask any online casino what their main source of revenue is, and the likely answer will be 'slots games'.

Slots are the game of choice for internet casino users, to the point that a 2021 Gambling Commission report found that they contributed 73% of the £4 billion in UK online casino game revenue for the previous year.

The rise of mobile slots and elaborate game features have turned many of them into an immersive experience, which means you can now get just as much enjoyment by playing for free as when staking money.

With slots being such a fundamental part of the online casino experience, and with such a diverse range to choose from, you'll probably want to know more about them. You might wonder how they work and what you should be wary of when playing them?

Casino Meter is here to help you with this. Our team has years of experience dealing with slots and their related issues. In this article, we're going to pool together all that knowledge to bring you an accessible, easy-to-read guide all about slot games.

A brief background to slots

Slots have a long and varied history stretching back to the days of the Wild West. In the 1890s, basic gambling machines dealt random poker hands to players in saloons, along with the odd prize.

The Liberty Bell machine soon elaborated on this idea and is thought to be the first-ever slot game. Its inventor Charles Fey replaced the poker cards with reels, and players hit the jackpot when they landed three Liberty Bell symbols.

Fruit machines, so-called because they awarded packs of fruit gum as prizes, were a variation of Fey's idea. The winning reel symbols told the player which type of gum they had won, and we still see the classic cherries, bananas, and plums in today's classic slot games.

It wasn't until the 1960s, though, that the first electromechanical slots came about: ones where you hit a button to spin the reels. One of the first was Bally's Money Honey. This was a big hit with its ability to automatically pay out 500 coins as a jackpot.

The trend spread across the United States with Las Vegas becoming particularly famous for its huge variety of electronic slot games.

Gaming technology continued to evolve. The widespread use of the computer microchip in the 1980s paved the way for video slots, progressive jackpots and, eventually, the first online slots, which started to appear in the late 1990s.

From the first basic internet games (Microgaming's Cash Splash was the pioneer) to today, the online slots' journey has been eventful.

Modern slots resemble video games with stunning graphics and immersive gameplay and features. HTML-5 technology, meanwhile, makes it just as likely that you'll play slots from a mobile casino as on your browser, without a drop in quality.

To put it simply, online slot games are booming. And, with technology improving at a breakneck pace, it feels like there is much, much more to come.

How slots work (and make money)

Online slots operate on a similar basis to traditional land-based machines in that they both employ a Random Number Generator (RNG).

An RNG is a mechanism that produces a completely random number each time it's put into action. In slot games, this randomness ensures that each spin is fair and free from bias.

Traditionally, the RNG worked via mechanical reels, however, online slots developers have replaced this with a computer algorithm which follows the same principles.

How slots make money

With each game being completely random and fair, you may wonder how online casinos make a profit. The answer lies in a mathematical construct known as the 'house edge'. This is a slight advantage (in favour of the casino) that's built into the mechanics of every slot game.

Typically, the house edge is between 1 to 5% of the total stake. Simply put, the longer you play, the more likely you are to lose money thanks to the house edge.

On the flip side, the amount left after we take off the house edge is known as the Return to Player (RTP). This is the theoretical expected return over time. You'll normally find this percentage in the information box next to or in each game.

Here are a few examples with a £10 stake.

Game RTP 95% 92% 98%
Expected return £9.50 £9.20 £9.80
Expected casino profit £0.50 £0.80 £0.20

Slots variance (or volatility)

Every slot game has a different level of variance. This is a marker of how much your bankroll is likely to change as you play the game.

If you want to play for a longer time, then a low variance slot is better as it's likely to give you small, more frequent wins that keep your balance ticking along at similar levels.

High variance slots, however, have the potential to deliver rare, big wins, but they can quickly drain your funds if you're not careful.

As a player, you sometimes have the option to adjust the variance of a game by changing the number of active paylines. Decreasing them, and boosting the bet per line as a result, pushes the variance up. Increasing them has the opposite effect.

There are often 'Double or nothing' options or similar bonus features, too, which greatly increase volatility. Whatever you choose to do, be sure to keep safe gambling principles in mind, including only betting with what you can afford to lose and never gambling with borrowed money.

Frequently asked questions (FAQs)

How do I use my online casino bonus in slots games?

The crucial first step is to make sure your bonus is eligible for the slot game you'd like to play on. Sometimes games fall outside of the bonus's terms due to their high RTP.

Then, it's just a matter of clicking on the game title and starting to play. If your bonus consists of prepaid spins, you'll see the amount reduce for each spin, whereas your casino balance will go down if you were awarded extra credit.

Remember that some slot games contribute less to wagering requirements (WR) than others – for more information on how this works, check out our guide to casino bonuses .

Are there any good slots strategies out there?

Slots are pure games of chance, so no strategy can ensure a positive financial return. In fact, the longer you play a slot, the more likely you are to lose money thanks to the house edge.

However, as we mentioned earlier with changing the number of paylines, there are certain tweaks you can make to some slots to adjust its volatility. There are also certain gambling styles that may improve the chances of a big payout.

Are slots the most lucrative casino game?

We should add a word to that question: slots are potentially the most lucrative casino game because of their high win amounts, including progressive jackpots and features.

However, landing a big slots win is extremely rare. In fact, the average slots' RTP is lower than in games like blackjack and video poker, so if you want to make money, you're mathematically playing the wrong game.

Viewing slots as a form of entertainment which you pay for, rather than a moneymaking scheme, is much better – not to mention healthier.

Are slots games safe?

In terms of game safety, online slots are extremely secure. Their use of RNG technology ensures that you'll get a fair result for every spin.

However, it's essential to find a reputable casino to play them at to avoid problems. Every casino you see here on Casino Meter is licensed by the UK Gambling Commission which holds them to specific safety standards.

On top of that, we recommend you go to our list of online casinos and choose from those with the highest Meter ratings to improve your chances of a safe slots experience.