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How Do Slot Machines Work – Ultimate Guide

How Do Slot Machines Work – Ultimate Guide

Published on by Ben

Online slots have long held a prominent position at most online casinos, usually taking centre stage within the site’s main lobby. Even if your preferences lean towards other types of casino games, you’re likely aware of how popular online slots have become. The reason behind this is that slot providers, such as NetEnt, have imbued these games with all sorts of exciting features, free spins and huge potential wins. All it takes is one spin of the reels and if the symbols land in the right positions you could be walking away with massive amounts of real money winnings.

Yet many players are unfamiliar with how slot machines work, which is understandable because they can seem confusing at first glance. Plus there’s the fact that each slot features its own form of unique gameplay. Although some games utilise similar mechanics, their individual peculiarities differ from one slot to the next meaning there’s always something new and exciting to discover.

That’s why we’ve created the ultimate guide to online slots. We discuss exactly how slot machines work, how their highly lucrative features can be triggered and how certain factors dictate their general gameplay. Once armed with this knowledge, you’ll be able to use the information within this article to your advantage and potentially becomes the next big slot winner!

Online Slot RTP – Your Theoretical Returns

If you’ve played online slots for any period of time you’ve likely come across this term before and are aware of its importance. RTP is a factor that dictates a slot’s theoretical returns over an extensive number of spins – estimating how much a game pays out for how much goes in.

It stands for Return To Player and you’ll see it expressed as a percentage, either when you first load up a game or within its information panel. Nowadays, the RTP of most online slots is usually in the region of 94% – 97%, but there are a few games that fall either side of this range. A prime example is one of the many popular NetEnt slots: Mega Joker, which has a 99.00% RTP.

As a rule of thumb the higher the RTP percentage a slot has, the better because it means, at least theoretically, it’s expected to pay out more. For example, a slot with a 96% RTP is expected to pay €96 for every €100 that is staked. However, it’s greatly important to bear in mind that this information is calculated over millions of spins. So, during a typical slot session, results will vary. You could walk away with a vast amount of winnings or you could just as easily lose quite a lot of money.

That being said, this is part of what makes playing online slots exciting – anything can happen when you spin the reels. If a game were to pay back exactly €96 after 100 spins at a €1 stake it wouldn’t be fun to play. Obviously wins are important, but the sense of anticipation that each spin brings can be invigorating. That next press of the spin button could be all that stands in your way of a free spins feature and a phenomenal win.

Online Slot Volatility – Risk Versus Reward

Another key element that determines an online slot’s gameplay is volatility, or variance as it’s sometimes referred to. Essentially, this indicates the behaviour of a game and refers to the frequency of payouts, how much the wins are worth and how much inherent risk is involved when playing a particular slot.

Some online slots favour infrequent large wins, which can also present long dry spells. These are known as high volatility slots. These also have the potential to land a series of big wins in a short space of time but it must be said that it’s a rare occurrence. NetEnt has long been known for releasing some of the most exciting high variance slots, with titles such as Dead or Alive II, Vikings and The Wish Master often being considered amongst many fan favourites.

Conversely, low volatility slots feature frequent payouts, but it’s often the case that they’re of much lesser value than their high variance counterparts. Again, NetEnt has produced many fine examples of low volatility slots, many of which are often featured as part of an online casino’s welcome bonus or free spins offer. So, if you’re looking for regular wins we suggest you keep an eye out for games such as Starburst, Butterfly Staxx and the more recent Wilderland.

Ultimately, choosing high volatility slots or low volatility slots isn’t a ‘good’ or ‘bad’ decision. It’s entirely a matter of personal preference and gambling style. However, one thing we would say is that because slot providers don’t always provide information relating to a game’s volatility it’s advisable to play for free, in demo mode, first. That way you’ll be able to get a feel for the overall gameplay before you play for real money.

Hit Frequency

Hit frequency often ties neatly into an online slot’s volatility. The two work in combination to form the overall reward structure for a game. Simply put, hit frequency refers to how often a slot game will create a winning combination as opposed to a losing one and how often certain features are likely to trigger.

As you’re probably aware, not every spin of an online slot results in a win and certain symbol combinations are often worth less than your original stake. However, any win that lands, regardless of its value, is as a result of the game’s hit frequency.

Although these details aren’t usually listed within an online slot’s information panel, the hit frequency is usually expressed as a percentage. For example, NetEnt’s recently released Gems of Adoria has the following hit frequencies:


  • Any win: 22.1%
  • Entry Into Free Spins: 1 in 164 spins
  • Flipping Symbols Frequency: 5.1%
  • Striking Wilds Frequency: 2.6%


Now, as you can see, Gems of Adoria has a 22.1% hit frequency for a win of any value. Throughout your time playing that means the slot averages a winning combination roughly once every 5 spins, including payouts that are of less value than your stake. Free Spins are expected to trigger once every 164 spins. However, you must remember that it doesn’t mean after 164 spins free spins are guaranteed. The remaining values relate to how often certain base game features activate.

Online Slot Free Spins And Features

Special features, free spins and huge potential wins – these are the main reasons many people love playing online slots. However, if you’re new to the whole experience you may be unaware as to what they are and how they work.

Depending upon what type of slot game you play, there may be additional features to activate. Some occur randomly, whilst others require specific symbols to appear on the reels. Now, these features aren’t included in every game. Certain releases, such as those described as classic slots, instead solely rely on symbol combinations to generate payouts.

In most situations, the way to activate a slot’s main bonus feature is by landing Scatter symbols on the reels. If present, the game’s paytable will indicate which symbol is the Scatter and how many need to appear on the reels in order to trigger the feature. If you are fortunate enough to activate a free spins feature, many of them offer the best chance to land the biggest payouts. This is because many online slots utilise additional mechanics within these features, which are not present during the base game. These can include wild symbols, multipliers, expanding symbols and many other unique enhancements.

Your free spins will then play out at the triggering stake until the counter reaches zero. All wins gained during free spins accumulate and are awarded after the bonus has ended. What makes these online slot features so exciting is that they can also often be retriggered, granting you even more opportunities to land additional wins.

Aside from free spins, there are also some features that can occur at random intervals during the base game. These may pop up before, during or after the reels spin and offer additional chances to land winning combinations.

So, if you’re looking for a feature-rich online slot, take a look at any of our casino game reviews to discover what mysterious gameplay elements may lie in store!

Maximum Payouts & Progressive Jackpots

Many people may play online slots for enjoyment, but the ultimate goal is to win. Any game that you choose will have fixed payouts that are determined by your overall stake and defined symbol combinations. The more symbols that appear on a winning pay line, the larger your win will be.

It’s worth mentioning that some symbols are worth much more than others – these are often referred to as premium symbols. If these were to land on every reel, on an active pay line, you could be looking at the slot’s maximum payout. All of this information will be displayed in the game’s paytable, which is often located within the information panel below the reels.

However, the total amount that you can potentially win per spin is limited by the game’s maximum payout. This is normally displayed as a certain number of times your stake, with many NetEnt releases offering possible real money wins of over 5,000x.

Yet some slots, however, can generate even larger payouts. One such game is Dead or Alive II. This widely-loved slot has a maximum win of 111,111x your stake, which means you have the chance to win a life-changing sum of money should you choose to play. However, this isn’t awarded via regular symbol combinations in the base game. Instead, you’ll need to trigger the free spins feature and be extremely lucky to land specific wild symbol combinations. As you’d expect, it doesn’t happen often. In fact, it’s an extremely volatile feature and can be underwhelming at times, but all it takes is for it to happen once and you’ll be walking on cloud nine for a long time to come.

Elsewhere, there are many fine NetEnt jackpot slots to play. Some, such as Hall of Gods and Mega Fortune, feature networked jackpots, which increase each time a real money wager is placed at any NetEnt casino that offers the game. As such, the huge prizes that are available can also be won at any of these sites – they’re not limited to a specific online casino. So, wherever you choose to play make sure to keep an eye out for these jackpot slots. They not only feature impressive gameplay and interesting features, but also some of the largest prizes available anywhere on the internet!

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Ben Boland

Ben Boland

Content Writer

Like his chum James, Ben is another bearded Brit that has made the transition from formal journalism training to the beautifully claustrophobic Mediterranean island of Malta. There he is a Content Writer for NetEnt Casino, ensuring that all utterances are legible and – most importantly – accurate.

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