Guide on How Online Slot Machines Work

Slot machines on mobile

Content Editor, Nemanja

Last updated on 9th April 2024

Published: 25/02/2019

Categories: News, Guides, Jackpots and Slots Guides

The one and only Guide for how online slots work

This is the perfect guide if you are entirely new to online casino and want to know what a slot machine is or how it works. You will learn the basic mechanic of how a slot machine is programmed and the mathematics behind that make them thrilling to play.

Let’s start with the definition: Slots meaning

Once for all, let’s define the word slot: It’s a casino game of chance, with a set of reels, populated with different types of symbols. In one game round the reels will spin and then stop. The wins are calculated using the new positions of the symbols on the reels after they stopped.

As one of the most beloved and popular casino games, Slot machines have several different names across the globe. I will go through the most common; Fruites, Fruit Machines, One armed Bandits, Video slots, online slots, pokies and so on. There is no real difference between these name; they all mean more or less the same thing.

  • Fruites / Fruit Machines – Commonly used in Great Britain and are for the physical slot machines in bars etc. That only have fruit symbols.
  • One Armed Bandits – Used for the first physical slot machines. Which had an arm on the side; you had to pull to spin the reels.
  • Pokies – Australian slang for all types of slot machines, both land-based and online slots.
  • Video Slots – Slot machines played on a video screen. All slot machines online are video slots, most slots in land-based have been changed from mechanical to video as well.
  • Slot Machine – a name for all the types of slot machines!
Slot Machine Meaning: It’s a casino game of chance, with a set of reels, populated with different types of symbols. In one game around the reels will spin and then stop. The wins are calculated using the new positions of the symbols on the reels after they stopped.

The invention of the slot machine

To understand how casino slots of today work, we have to travel back to when the first slot machine was created. Let’s embark on this journey together that takes us all the way back to late 1800.

Charles Fey is the creator and father of the first slot machine. The premise and mechanics of slots are still the same to this today. Charles named the first slot machine Liberty Bell, named after the highest paying symbol in the machine the Bell.

Screenshot of Invention of Slot Machine
Photo of Charles Fay’s Liberty Bell – The first slot machine ever created!

The Liberty Bell had three individual spinning reels, five symbols and one winning pay line. The symbols were: Horseshoe, diamond, spade, heart and the bell. Symbols you still frequently see today!

With only one winning pay line – it was easy for anyone to understand how to win, simply line up the same symbol on each reel, and you have a win.

The one-armed bandit: Does not come from the old tv-show, Twin-Peaks where there is a bandit with one arm. No, it Comes from Liberty Bell, as you can see above in the picture it had an arm you had to pull to start a new spin. The sequel slot machines had the same mechanic for years to come.

How online slots function – the basics

Believe it or not but, today’s slot machines work in the same way as they first did when Charles Fey released the Liberty Bell. Today, however, the slot machines of today do not have physical reels, but virtual reels.

Screenshot of Online Slots Function

Each reel stripe is populated with the different symbols in the slot machine and can have a different amount of symbols added to them – this is the base mechanic to decide, the odds and number of possible ways to win.

Screenshot of Reel Strip of Slot Machine

Virtual reels: is the same as mechanical reels, except there is an infinite amount of symbols that can be added – allowing online machines have more possible winning combinations than any other casino game!

How the outcome is calculated

Today, online slot machines are far more sophisticated than the Liberty Bell, and it quickly becomes confusing explaining all the different elements and how they are tied together. Hence why I will use the Liberty Bell machine as an example to give you the idea of how the odds in a slot machine is calculated. After all the slot machines online today use the same basic premise.

So how is it possible for slot machines to have so many different winning possibilities?

Example Liberty Bell:

3-reel slot, with 5 symbols on each reel. There would be 5 x 5 x 5 = 125 winning combinations.

Well, that doesn’t sound overwhelming?

It’s not, but you have to remember Liberty Bell was the first of it’s kind. With today’s video slots and their virtual reels, the programmers can add an unlimited number of symbols per reel.

Let take another example, and in this example, it’s 20 symbols per reel instead. Which gives us 20 x 20 x 20 = 8000 possible combinations.

Today the slot machine most often has 5 reels. And features Liberty bell didn’t have, like Wild Symbols and in-game bonus rounds. With more reels and features, the number of combinations becomes exponential and quickly, the slot machine will have winning combinations to be up to into billions!

How the payout is calculated

Each Reel has a certain amount of symbols on them, the more of the same symbol on the reels – the lower payout will that symbol have. As the chances of connecting a winning combination will be higher.

Let’s take the Liberty Bell as an example again, but slightly modify the number of symbols for the sake of this example. Liberty bell as you remember is a 3 reel slot game.

Our simplified slot machine

In this example, we will only have 4 different symbols: one Bell, two horseshoes, three diamonds and four hearts per reel. This would give us 1,000 possible combinations and RTP (return to player) of 83.2% with the pay table below.

Screenshot of Simplified Slot Machine

  • Each of the three reels will have a total of 10 symbols. Every reel has one Bell – that’s the highest paying symbol.
  • Each reel also has two horseshoes, three diamonds and four hearts.
  • This gives us 1,000 possible winning combinations – 10 symbols times 10 symbols times 10 symbols.
  • Only one combination – or 1 x 1 x 1 – will be three Bells.
  • 8 combinations will be 3 horseshoes, 27 will be 3 diamonds, and 64 will be 3 hearts.
  • 900 of the 1,000 combinations mix different symbols – which won’t be a win at all.

Our now modified Liberty Bell slot machine pays 160 on three Bells, 25 on three Horseshoes, 8 on three Diamonds and 4 on three Hearts. Multiplied by the frequency of wins, those payoffs total 832 coins. By paying less than the true odds of the game (100%), the machine has a payout of 83.2%. Luckily for you and me, an online slot machine with this payout wouldn’t pass certification today as it is a requirement that it has to have a minimum payout of 90-92%.

Calculation: If you wonder how I got to 83.2%. Start from the first row in the paytable picture above, take each “number of combination” times “coins per win”, and you get “Total coins paid”. Then sum “Total coins paid” for each symbol, and you get 832. Remember that the total of combinations was 1000. That gives us 83.2% in RTP Return To Player

RNG – Random Number Generator

So, now you know the premise of how all slot machine mechanically/virtually looks behind the screen. But how does the Slot machine online know if it was a win or not?

All online slot providers, reviewed here at G2G and available at any of our recommended online casinos use an RNG. RNG stands for Random Number Generator – it’s a software that secures the game is random and not predetermined.

Hence you could say it’s the RNG that secures for us that the slot machines are fair. And that they are not rigged in favour of the slot provider or the online casino. Thus all slot machines are tested by an independent test partner like eCogra before a release – to secure the slot machine truly is providing random results.

Important: All the Indian casinos reviewed here at G2G are not only just with their game offering, but you are guaranteed not to have any issues withdrawal your winnings.

So how does the Random Number Generator work?

The Random number generator exists of 1 and 0 that are calculated by sophisticated algorithms. The combination of 1 and 0 decides what symbols and how they will land on the game screen. Thus slot machines aren’t 100% up to chance since it’s algorithms behind them deciding the winning number. The algorithms are so advanced there is no way to determine whether next spin or not will be a win or no win. On a philosophical level, you can always argue that nothing ever is entirely random!

So how does it work when I play online?

  1. You click the spin button – the same time the RNG generates a random number in lightning speed.
  2. The Game engine of the slot uses this random number to calculate how each reel should stop.
  3. The Outcome is calculated of the spin and also the possible winnings.
  4. Step 1-3 happens in a split millisecond just as you start the spin on your screen all calculations will already have been made. Around 3 seconds later your spin is over, and the outcome of the spin is presented.

How does the Bonus Round and Free Spins work?

The same goes for the Bonus game and free spins – most of the time the total win of free spins is already be calculated before you have played through your first free spin in the Free Spins round. A free Spins round with 10 free Spins is a matter of fact represented as one game round. But for us the player it may look like 10 Free Spins.

This doesn’t mean it’s rigged – it’s just how it’s programmed. I’ve several times lost my connection in the middle of free spins on a game without “restore state”, meaning the game picks up the free spins where I left. Instead, I’ve started the game, and the total win is presented. If the slot machine wasn’t programmed in this way, the Free Spins round would be lost, and I wouldn’t get any winnings at all. That is what I would call unfair!

RTP or Return to Player

RTP stands for Return To Player and is the calculated payout of a slot machine. Online it ranges from 90-98%, in land-based, where there is less strict control it could be anywhere from 70-92% on the slot machines. Thus it’s better to play online as you have far better chances to win. No matter if you play online or offline, what we always will know, is that the RTP will be less than 100%, as otherwise neither the casino provider or the online casino would make any money on it.

So what does RTP mean? To get a mathematically correct RTP the slot games are tested in specific software – allowing to simulate several billion spins in a short period. These spin determine what is called expected RTP. Contrary to actual RTP that you have when you play.

The actual RTP will change from each session you play. The expected RTP will always be true, but to get it you will have to play billions of spins.

There is a way to many players on different forums that throw accusations at game providers that the RTP in the game is wrong or that they can change it when you play the game. These players often proudly claim to have played several thousand sometimes even hundreds of thousands of spin.

Well, even if they have played that “many” spins – it’s still such a small sample out of the billions of spins the RTP in the game was tested for. In such a small sample, you are more likely to find big extremes like really low RTP or a really high RTP. But no one would never complain about an RTP to high? Right!

So by now, you are probably wondering, why does the actual RTP in slots vary so much?

Variance – Low and High Volatility

Besides the RTP, it’s the volatility that creates the magic in a slot game. Volatility is the secret ingredients in a slot machine that makes it come alive. Used correctly it gives the slot the perfect balance, to be entertaining and give the feeling of a big win is right around the corner. Misused, you get filled with a feeling it’s an impossible way to win at all in the slot machine.

What is the difference between volatility

The variance decided as high and low can be simplified explained like this:

  • High variance slot – Have few wins a lot of dead spins, but when you win you win big.
  • Low variance slot – Have a lot of wins, often you won’t even win the bet back. There are very few or none really big wins.
  • Medium variance slot – A mix in-between high and low.

Screenshot of Difference Between Volatility

Take a look at this graph above. On the Y axel, you can see the percentage of win distribution. On the X axel, you can see the win amount times the bet. As you can see most wins are between 2-500x bet.

Looking at this graph – do you think it’s a high, low or medium volatile slot?

Medium volatile. As you can see most of the wins are distributed relatively equally. There are no big spikes around the super big wins and the win distribution of smaller wins peaks around 2-5x.

How is volatility calculated?

There is no scientific formula and grading scale for the volatility of slot machines. All online slot providers themselves do the calculations and decide the volatility based on their metrics. This means it’s may be difficult for the average player to know, but we at G2G add the volatility given by the Game provider in all our slot reviews. Head over to our free slot casino and see which volatility suit you the best!

What should I play?

It’s not something I can answer – you will have to try for yourself and see what type of volatility suits you.

But generally High volatile slot games are most popular among experienced players, most of us who plays a lot of slot machines end up here. Why? The cheer possibilities to win big are greater than to play a low volatile slot game. The session may be short or frustrated as you may be very unlucky and not win at all. But that ways up on the sessions when you hit it big!

Low volatile slot machines often most popular among beginners casino players. A lot of the focus in these games are on win animations and animations on the character to keep the player engage. This is a lot of fun, in the beginning, to familiarise yourself with how slot machine work, but winning big is not going to happen – it’s more used for long sessions.

Medium volatile slot machines – Generally have something that suits everyone, a great example of a medium volatile slot is Starburst the most popular online slot machine in history!

FAQ – Slot Myths

To finish this guide, let’s go through common Slot myths:

Q: After a big win or Free Spins you are less likely to win again.

A: No, that is not how probability work. Slot Machines or math do not have a memory. The chances of winning are the same for every spin.

Q: There is a dwarf behind the slot machines at the casino, and when you are close to winning big, he makes sure to push the reel an extra position, so you miss!

A: This one is true. 😉

Q: Online Casinos and Slot providers can change the RTP

A: Online this is not true, but in land-based casinos it is possible. A few online providers like IGT used however to have three different RTP alternatives on their slot releases ranging from 92-96% – where the online casino could choose which version they would want to put live.

Q: Slot Machines are rigged

A: No, they have an RTP of less than 100%. Which means in the long run – you will lose. The volatility, however, allows you to win in the short run.

Q: You can decide the outcome in a pick n click bonus game

A: Sorry to break it for you, no. If you read above how the Free Spins and bonus round work. You will know that it’s already a predetermined bonus round once you enter. The rest of the animations are just to keep it thrilling.

Q: Quick-stop / force stop – you can decide where the reels land

A: Some doesn’t call it skill-stop, for anything? But unfortunately, no you can’t change the outcome of a spin by stopping the reels with the stop function.

That’s all – I wish you the best of luck and may the slot gods be with you!