How Online Slots Work

How Online Slots Work - Hero Image

Slot games have been around for well over a century now, having been created by German inventor Charles Fey in San Francisco way back in 1894. Over the years slots have evolved as technology has advanced, and the slots we see today dwarf the simple 3 -reel machines that were common amongst those that played them at the turn of the twentieth century.

Whilst there’s certainly no shortage of physical slot machines in casinos across the globe, the vast majority of games can now be found on the internet, as there’s a huge demand for new and innovative online slots from thousands of enthusiastic players.

Online slots make up what is arguably one of the largest and most lucrative sectors of the gambling industry in this day and age, so it comes as very little surprise that a whole host of new online slot games are released practically every single day of the year.

The following guide will take you through every element of online slot games and how they work including the different types of slots, how to play them, how they're regulated and much more.

Slot game mechanics

We’ll begin with the basics! How to play online slots… Because without knowing how to play these games you’ll get nowhere fast! And if we’re honest, we’re not just playing these games because they’re a lot of fun, but because we want to be in with a chance of registering big money wins that can boost our bankrolls… So without further ado, let’s dive into it!

Reels & Rows Image

Reels & rows

Reels are the most important element of an online slot. They are the vertical parts of the game that spin top to bottom after players have set their stake and pressed play. Each game reel will show a different selection of randomly generated symbols with every spin.

Typically, most modern online slot games will have 5 reels and 3 or 4 rows of symbols, traditional slot machines on the other hand would just have 3 reels and three rows with a single payline running horizontally through the middle row. 

The reels and rows of online slots make up a complex grid forming multiple combinations of symbols, and therefore paylines (more on those later).

As online slots have gotten more intricate over the years developers have pushed the boundaries by introducing more game reels, more symbols, more paylines and therefore more winning combinations. 

Paylines Image


Without paylines there are no winners! Paylines determine whether or not the symbols that have landed on the reels form a winning combination. 

Back when slot machines were first introduced they only had a single payline, players had to match three symbols along this middle payline to win money. 

Most modern online slots will have anywhere between 10 and 243 paylines, however, there are some slots that offer players up to 117,649 ways to win due to the fact that they can fit up to 7 symbols on a single reel.

Paylines can run in a number of different directions, usually from left to right, diagonally and in various zig zag patterns. The more ways to win a game has, the wilder the paylines can be, meaning symbols don’t always have to line up next to each other in order for players to register a win.

Symbols Image


Every single slot game will feature a range of different symbols that are unique to that game, each symbol is allocated a set value, with some symbols being worth more than others.

Originally, slot machines used symbols such as horseshoes, diamonds, spades, hearts, and bells. Over time these symbols evolved and fruit symbols were introduced such as cherries, watermelon, oranges, bananas, grapes, lemons and apples.

When online slots became prevalent classic symbols still remained, but online slot developers would begin using iconography from playing cards such as the suits and pips. The suits used are Clubs, Diamonds, Hearts, Spades and the pips are 9, 10, Jack, Queen, King, Ace.

Today, most slots use the aforementioned playing card symbols as low-value symbols in their games, whilst using heavily themed symbols that match the game’s design as high-value ones.

Almost all games also feature two or three special symbols, these are wilds, scatters and bonus symbols. Wild symbols are symbols that will stand in for any symbol (except for scatters) to help form a winning combination. Scatter symbols trigger free spins when a certain number of them land anywhere on the game reels, even outside of a winning payline. Bonus symbols essentially do the same as scatters, but trigger a different bonus feature or a jackpot.

Bets & Coins Image

Bet level & coin value

The bet level and coin value are two features that many online slots (in particular older ones) utilise. Both of these adjustable components relate directly to how much players are spending on each and every spin of the reels.

The first thing you must understand is that there’s a distinct difference between coin value and actual cost of each spin, it’s quite easy to jump to the assumption that both are the same. 

Most online slots use coins instead of currency for bets and wins. A winning combination, for example, may pay out 100 coins as opposed to £10. Having a common currency simplifies the overall experience and avoids complications associated with different currencies and denominations around the world.

Some slots allow players to adjust the coin value which in turn will determine your stake per spin and ultimately the total amount you can potentially win. The overall stake can be increased or decreased further by adjusting the bet level.

Similarly, some slots have adjustable paylines meaning players can select the number of active paylines. This is controlled by the ‘Bet Level’, also referred to as the ‘Lines’ bet. The higher the bet level, the higher the number of active paylines and so the higher the stake, but also potential winnings combinations.

For example, if you’re playing a 20 payline slot at bet level 1 with a coin value of 0.01 then you will be playing on one payline at an overall cost of 0.01.

If you were to adjust your bet level to the maximum of 20 (meaning you’re playing along all 20 of the game’s paylines) with the coin value still set at 0.01 then your overall stake would increase to 0.20.

Other slots have non-adjustable paylines (known as ‘fixed payline slots’) but will still have a bet level option. Changing the bet level here will still do the same thing in terms of adjusting your overall stake, however, in this case you’d still have all of the available paylines available to you.

Ultimately, slots that feature both an adjustable bet level and coin value allow you to be more flexible with the amount you stake. You don’t tend to see too many games like this now, as they’re considered to be confusing and can deter new (and experienced) players.  However, they do still exist and remain popular with those who prefer Penny Slots where stakes can be reduced to as little as 1p per spin.

Paytable Image


The paytable is a screen that can be accessed through each online slot’s game menu. It displays the values of each individual symbol (including scatters, wilds and bonus symbols) that appear in the game, as well as displaying the various directions each and every payline goes in (assuming this is a 10-25 payline slot and not one with hundreds/thousands of paylines).

The paytable will also often display other important information that players should always be aware of, this includes the game’s RTP (return to player), the maximum win potential of the slot and information on each bonus feature and how to trigger it.

Bonus Features Image

Bonus features

Almost all modern online slots come complete with a wide range of bonus features! These are hugely lucrative mini-games that can be triggered by landing a specific set of symbols in a specific order on the reels.

The most common bonus feature found in almost every game is free spins, these are a set of spins that are usually triggered by landing 3 scatter symbols anywhere on the game reels. 

Free spins allow players to accumulate successive wins at absolutely no cost to themselves (other than the initial spin that triggered the free spin bonus). The more scatter symbols players land on the reels (usually between 3 and 5), the more free spins they’ll receive in one go. It’s also possible for players to re-trigger free spins during the bonus.

The more intricate and well designed the game, the more intricate and well designed the free spins bonus will be. Some developers will include bonus modifiers (events that change the way the bonus game plays) during free spins, this means that players can potentially trigger much larger wins. 

These modifiers might be something like sticky wilds (when symbols stay in one place for the duration of the feature), expanding reels (where more symbols can land on a larger single reel) or the promise of additional high-paying symbols landing during free spins.

Other bonus features include pick and click mini-games, in which players are tasked with picking certain items in order to collect win multipliers, wheel-of-fortunes and symbol substitutions just to name a few.

There are no rules that state whether online slots should feature bonuses, however, in this day and age it’s come to be expected that a title will at least offer players free spins, if not something equally as lucrative. Realistically most players will choose to ignore games that don’t have bonus features unless they have huge perks such as a high RTP or have the potential to pay out thousands, if not millions in jackpots.

Jackpots Image


Some online slots will feature jackpots! These are huge massive sums of money that can be won randomly on any spin of the game (this includes losing spins), or by triggering a specific combination of symbols and then playing a mini-game such as a pick and click bonus or wheel-of-fortune to determine how much is won.

There are several different types of jackpots players can win trigger when playing jackpot slots, firstly we have networked progressive jackpots. These are large jackpots that are spread across multiple online slot sites that continue to grow in size every time a player spins the reels, as a small percentage of their bet goes towards funding the jackpot.

Sometimes a networked jackpot will be spread across multiple games in an online slot series such as Age of the Gods or Kingdoms Rise, or it might be a progressive jackpot that’s spread across a developer’s entire portfolio of slot games such as the Jackpot King, Mega Drop Jackpot or the WowPot!

Progressive jackpots can either be placed into one large pot which tends to pay out once every few months, or it can be spread out across multiple pots, some of which will have certain criteria to meet and will pay out on an hourly, daily or weekly basis, such as Red Tiger’s Daily Jackpot

The other kind of jackpot you will often find in online slots are local jackpots, these tend to be smaller jackpots that are linked to just one slot. They’ll either be fixed at a certain amount of money, or they’ll be progressive whereby anyone playing that slot will contribute to the prize fund.

What are the different types of online slots?

Back in the early days there was just one type of slot available that featured just 3 reels and 1 payline. As slots evolved they grew to 5 reels and then eventually when intricate electronic slot machines arrived in casinos more paylines were added to make them more attractive to players.

Once slots made it online then all trends were bucked. There is now an entire library of different style slots that players can choose from, this includes games on both ends of the spectrum, some of which are simple and easy to play, others are intricate and will require a little bit of learning before spinning the reels. Here are just some of the most popular types of online slot:-

Video slots

The modern online slots that we know and love today are often referred to as video slots. These are heavily themed online slot games that can have any number of reels and paylines, and have multiple bonus features that make for exciting and varied gameplay. 

3-reel slots

As mentioned earlier, the classic slot machine released back in 1984 only featured 3-reel slots and a single payline. This isn’t a very popular slot layout today, as it’s not particularly exciting, however a handful of developers have opted to release modified 3-reel slots with some success. These games are ideal for beginners and casual players who do not wish to learn mechanics.

5-reel slots

5-reel slots are the industry standard for most modern online slots, there’s nothing to stop developers from deviating from this layout, but 5 reels tend to work perfectly for most players as it’s what they know. They also allow for a higher amount of paylines, combinations and other mechanics as opposed to a 3 reel slot.

Fixed/variable paylines

Depending on what game you’re playing you will either be playing with fixed or variable paylines. Traditional online slots mainly feature variable paylines which means that players must increase their stake in order to unlock more paylines. Playing with the lowest stake would see punters playing along just one payline, whilst upping their bet level would see more paylines activate.

Fixed paylines on the other hand are much more common nowadays, these are games that automatically have all of the paylines activated, regardless of stake. This means that players have a bigger chance of winning or triggering a bonus feature as there are more opportunities to win, even when playing with the bare minimum per spin.

There’s no right or wrong when it comes to deciding which style slot to play, however, if you’re playing on a budget then perhaps one with variable paylines would be preferable as you can usually play with a much lower stake in comparison to that of a fixed payline slot.


There’s nothing quite as iconic as Megaways slots, these are a relatively new type of slot that was pioneered by Australian developer Big Time Gaming when they released Bonanza Megaways in 2016. 

These slots are known for having 117,649 ways to win, which means that there are a lot of opportunities to register winning spins. The Megaways mechanic works thanks to an innovation known as Random Reel Modifier technology that sees the number of symbols on each reel change after every spin, allowing for more combinations and therefore more ways to win.

Big Time Gaming licenses out the Megaways engine to other online slot developers, which is why you’ll see well-known developers such as Red Tiger Gaming, Blueprint Gaming and NetEnt release Megaways slots as well.

Best Megaways Slots

Grid Slots

Grid slots are online slots that do not look or feel like online slots at all. Rather than being played on reels, they’re instead played on a game grid. They very much resemble the classic arcade game Bejeweled or more modern mobile game Candy Crush.

Players register winning spins by having a number of matching symbols grouped together on the screen. After a winning spin has occurred they're removed from the game grid and new symbols fall into place, leading to additional winning combinations. 

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Are online slots fair?

An age old question that gets asked time and again by absolutely anyone thinking about playing an online slot game is ‘are they fair’... The short answer is, yes! Online slot games are fair on the condition that you’re playing them at a tried and tested casino that has received a license from a trusted slot site regulator.

All slots must comply with the regulators technical standards and requirements. This means that they need to be thoroughly tested over millions of spins using industry-trusted software that ensures they're safe to play before they ever reach an online casino lobby.

In addition to this, every single online slot utilises a random number generator (RNG), this generator creates random sequences every time the game reels are spun to ensure that the slot is fair and is producing a truly random outcome in terms of which symbols appear and in which order.

At times it may seem as if the slot is working against the player after a particularly bad run of spins, however this is purely down to chance and nothing else. It’s just as likely that a player will experience a good run of spins as they are to experience a bad run of spins.

The same logic can be applied to online slot jackpots, a player could win a £1,000,000 jackpot and then theoretically win the £1,000,000 jackpot in the spin that immediately follows. It’s all a game of chance and RNG means that nobody truly knows what will happen.

Developer licenses, testing & audits

Before any online slot game can be released and played by members of the general public they first must go through rigorous testing and audits in order to gain a license, certifying them as safe to play in a particular jurisdiction.

There are multiple testing agencies out there that can certify a slot as safe, those that are most well known include eCORGA, Gaming Laboratories International and iTech Labs. These agencies will test games by spinning the reels millions of times in order to ensure that the game output is randomly generated, unpredictable and that outcomes cannot be reproduced.

What is RTP?

The RTP (return to player) signifies the amount of money as a percentage that a player can expect to receive back from a specific game over time.

If an online slot game has an RTP of 100% this would mean that over time if players were to spend £100 playing this slot they would eventually break even, as 100% of what they’ve staked on the game would be returned to them in winnings. 

That being said, there are no instances of online slot games having an RTP of 100%. The industry average for a good and fair online slot is 96%, the remaining 4% being the casino and slot developer’s profit. 

So, if you were to wager £100 playing a slot with an RTP of 96% theoretically you should see returns of at least £96 over a sustained period of time.

Most online slots have RTPs that range from around 88% - 97%. There may be multiple reasons a slot has a below-average RTP, some of which are fair, such as when it features a progressive jackpot or a generous bonus feature that triggers often. Frustratingly, some slot developers will create games with disappointingly low RTPs so that they do not pay out as much.

What is volatility?

Volatility (also commonly known as variance) refers to how predictable an online slot game is, and how often winning spins will occur. Almost all online slot games are split into one of three categories, low volatility, medium volatility and high volatility.

Low volatility slots are online slots that tend to pay out smaller sums of money at more regular intervals in comparison to medium and high volatility slots.

Medium volatility slots are online slots that are unpredictable and will sometimes pay out large sums of money to players and will sometimes payout small sums of money to players.

High volatility slots tend to pay out large sums of money to players less frequently compared to medium and low volatility slots.

Usually we recommend that players with a small bankroll opt to play low or medium volatility online slot games, this is because it’s easy for players to see their balance dry up very quickly when playing high volatility slots, as they tend to be very unforgiving.

If you have a larger bankroll, some patience, and are looking for big returns, then a high volatility slot might be more suitable for you as there’s where you are more likely to find the biggest payouts occurring, albeit not very often.

Who makes online slots?

Online slots are created by highly talented development studios from all around the world. There are literally hundreds, if not thousands of studios out there that have excelled in creating quality online slot games but only a handful are known for being the best of the best.

Arguably the most famous online slot developers in this day and age are NetEnt, Red Tiger Gaming, Big Time Gaming, Microgaming and Blueprint Gaming. Many online slot studios have their roots in traditional land-based casino gaming, with some successful developers operating in both spheres of the industry such as IGT, SG Digital, Barcrest and WMS.

If you play online slots long enough, you’ll begin to notice hallmarks of each individual developer, such as unique design elements or features and mechanics that aren’t seen in other games, for example Wazdan slots boast mechanics that allow players to set their own volatility, which is not something you can do in anyone else’s games.

Best Online Slot Developers

Online slot strategies: How to win

It’s not what you’re going to want to hear, but truthfully, there’s no sure fire way to beat online slots and ensure that they pay out every single time, this is because they utilise a random number generator as mentioned earlier on in the article.

The only way we suggest players can potentially find success with online slots is by sourcing the best and most generous casino bonuses that suit your needs, once you’ve done that then you’ll need to find eligible games that meet the criteria that you like to play with.

If you’re thinking of playing online slots with a limited budget, but still want to be in with a chance of picking up some big wins then you might think about playing low volatility slots that have a decent RTP, progressive jackpot and good bonus features. Admittedly, you’d be asking for a lot but somewhere out there will be a game that works right for you.

If you’re playing with a decent budget then you have a lot more scope, that being said we’d still recommend going for jackpot slots, or feature-rich slots that offer players plenty of opportunities to pick up hefty wins.

The reality is, like most things in life, you have to speculate to accumulate. The larger your stake on each spin, the larger each potential win is going to be, however, it’s still incredibly important to remain vigilant and gamble responsibly.

Online slot bonuses

There are two types of bonuses out there when we’re talking about online slots. First and foremost we have bonus rounds and features of a slot game, and then we have bonuses that players are gifted in return for signing up to play at a new slot site, in this section we’ll talk about the latter.

Many slot sites will offer brand new players bonuses that are directly tied to specific online slots, these bonuses will almost always come in the form of free spins. Once players have signed up and created an account at that specific casino, free spins will be credited to their account and they can begin playing with them right away.

The amount of free spins players receive will be completely dependent on the terms of the offer, operators may be more willing to give players a generous number of free spins if they’re first making an initial deposit and spending it at the casino, proving that they’re in it for the long-term.

If players receive a large number of free spins as part of a welcome bonus, such as 100 free spins on Starburst, then it may be that they’re made to use these free spins incrementally over time (such as 20 free spins per day over five days), or after depositing and spending a set amount of money. 

This is because casinos would be taking a bigger risk in the long term if players were given 100 spins in one go as they could use all of their free spins at once, withdraw any winnings and never be seen again.

Where to play online slots & get free spins

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Here at Slot Gods we’ve made it our personal mission to help you, the players, be as well informed and up-to-date as you possibly can be on all the very best online slots, slot sites and all the free spins that you can possibly get your hands on!

We’re just as passionate about online slots and slot sites as you are, so believe us when we say we’ll only deliver the most trusted and reliable games and sites that will give you the best bang for your buck!

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Frequently Asked Questions

  • What are online slot games?

    Online slot games are digital versions of the classic slot machines that can be found in pubs, bars and casinos around the world. Online slots are often filled with exciting additional features such as wild and scatter symbols, multipliers and free spin bonuses.

  • How do you pick a winning online slot?

    There's no true way of knowing whether an online slot will win or not, however, it's always advised to go for a slot that offers players a fair RTP (return to player) that's 96% or above or one that has lucrative bonus rounds and mechanics.

  • How do I find the best slot games?

    A good way to find the best slot games is to read in-depth reviews of each slot game before you play them. These reviews will give you a good idea of whether they're worth playing and offer value for money.

  • Can I play free slots online?

    Yes, many sites such as Slot Gods offer players the opportunity to play demo slots for free.

  • How random are online slots?

    Online slot games utilise software known as random number generators which ensure that each spin is completely random and fair. These random number generators are regulated and tested to the highest of standards on a regular basis to ensure they are always 100% random.

  • Is there any way of knowing when a slot will pay out?

    There's no way of knowing when a slot will pay out or whether a slot is 'hot' or 'cold'... The only time you can be sure a slot is going to pay out is with 'must drop' progressive jackpots that must pay out before they reach a certain amount or before a certain time.

  • What's the best online slot to play as a beginner?

    The best online slots to play as a beginner are those that do not overcomplicate things with a large number of paylines or intricate bonus rounds and mechanics. A good example of this is NetEnt's Starburst and Red Tiger Gaming's Mystery Reels.

  • Is it better to stake the max bet on online slots?

    Not necessarily. Many online slots do pay out large sums of money on smaller stakes. However, playing slots with the maximum stake often leads to big wins and can trigger progressive jackpots.

  • Do slot sites track how much you've won on slots?

    Online slot sites can see how much money you've won or lost over time (and will give you access to this data), but they will not penalise you for winning money from them. They may get in touch if they're concerned about your spend or wish to offer you extra rewards.

  • Should you stick to one online slot or play multiple slots?

    If you find an online slot that feels right for you then there's nothing to stop you from sticking to just that game! However, there are so many online slots out there that offer different experiences that are all well worth playing.