How Do Online Slots Work?

The Science Behind Online Slot Machines and Common Game Mechanics Explained

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Online slot games have a wide array of features and mechanics. In this article, we’ll explain just how they work and what your chances of winning on them are. 

Random Number Generators

No matter if you play a classic slot or a video slot, they all run on a random number generator (RNG). An RNG is what decides if you win or lose on each spin, and this is completely random. Neither you nor the casino can influence if you win or not, and this is what makes the game fair.

In reality, the RNG is the game. All the game features, themes, paylines, and graphics are just gimmicks. For example, when you have the chance to make a big win and the reels slow down, that’s just for entertainment. The result of the game round has been decided as soon as you pressed the spin button.

But without the gimmicks, playing slots online wouldn’t be much fun, and it’s good to know that an RNG generates random numbers to create results. As long as one of those is used, you know you have a fair chance of winning, or at least, the same chance as all other players. 

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Understanding Volatility/Variance in Slots

The RTP will decide the winning chances in the very long run, but it won’t really impact the short run. What’s much more important short term is the volatility in the slot, which is also called the slot variance. 

A slot’s volatility can be low, low to medium, medium, medium to high, or high. These are the common denominators slot providers use to describe the variance. 

What it really tells you is how likely it is that you’ll win on each spin. Low-volatility slots pay out often. High-volatility slots pay out less frequently. Therefore, low-volatility slots will pay out smaller wins, while high-volatility slots typically give bigger wins. 

Usually, we’ll say that a slot with low volatility is good for casual players and those playing just for fun. You can play for a long time with your bankroll because your balance won’t change much either up or down. 

On the flip side, high volatility is good for high rollers or other players who are not averse to risk. Your bankroll might not last through many spins, but if you do hit that big win, you’re golden. 

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The Casino’s Profit from Slot Machines

Casinos online as well as those that are land based are the only ones that always win long-term from slots. The percentages between the RTP of the slot and 100% is their profit. Typically, that means between 4% and 5% of all bets placed on the slot go to the casino. 

Of course, sometimes when players have won a huge amount, the casino might end up on the losing end, but, in the long run, they’ll always recuperate their winnings. There’s a reason why the saying “the house always wins” is as well-known as it is. However, it’s not like the casino gets to keep all profits from the games. They have operational costs that need to be paid, and game providers also want their cut. 

Typically, game providers get between 5% and 10% of all profits from their slot games. This will differ a bit from casino to casino and game provider to game provider. It all depends on what deal they have. Usually, there is no fixed cost for casinos to offer the games, as game providers get paid per revenue share. 

How Online Slot Games Are Made

Online slots are made by game providers, and there are hundreds of these companies. Some game studios have made thousands of casino games, while others only have a handful. Likewise, some only develop casino games, while others also develop online casino software.

Among all these game providers, there are typically between 30 and 50 new online slots being released every week, but not all casinos will add these games to their portfolios. 

We should also say that not all game providers cater to all markets. Players in some countries will have access to games from more than a hundred game providers at a casino. Players at offshore US casinos, on the other hand, are lucky to find ten providers. The most common ones are RTG and Betsoft.

Versions of Slot Machines

There are two main versions of slots, and here we’ll have a closer look at some of the typical aspects. 

Classic Slots

A classic slot is typically a 3-reel slot. The reels will most often show three symbols each, and they’ll have between 1 and 5 paylines. To get a win, you need to line up the same symbols on one of these lines.

As for symbols, the best classic online slots feature fruit, BARs, 7s, and sometimes jokers. However, these are the true old classics alike to the traditional slot machines you can play at land-based casinos. More modern versions of classic slots can have any theme, and thus any symbols.

What really is a hallmark of a class slot is that what you win simply comes from the paylines. There are no extra bonus features, and they are generally very simple slots games. The only bonus features you might find are a gamble feature or a super meter. 

Video Slots

Most games you find at real-money online slots apps nowadays are video slots. These are highly advanced slots, with loads of bonus rounds and features. You’ll find all features described in the game’s paytable.

Some years ago, they all used to have five reels showing three symbols each, and 20-25 paylines. Since then, new mechanics have been invented, and there is now no standard at all. Many of the best video slots have any number of reels or columns, and there can be several hundred ways to win. Even the paylines have been removed in some of these slot machines. 

The biggest attraction in a video slot is bonus games. Free spins game rounds, pick-and-click games, and even randomly triggered prizes can be found. These features give you the chance to make huge wins, which can’t be won in the base game. 

Slot Mechanics

In modern video slots, there are many game mechanics that can be used. Game mechanics are basically how slot machines work and how a player can win

The old standards of spinning reels are about to become outdated. New and more exciting gameplays await in slots fresh off the game provider production belts. 


The avalanche mechanic is fairly old by now, but it’s still popular. What it does is it replaces reels with columns, and when you win, the winning symbols disappear. Once that happens, new symbols fall down from the top, giving a new chance to win.

This game mechanic was one of the first ones that really became popular as an alternative to classic slot reels, mainly because it provides the chance to create more winning combinations on one spin and because avalanche wins tended to also give multipliers or other bonus features. Typically, the re-fall gives a better chance to win again or the chance to win more. 


One of the biggest game mechanics hits during the past couple of years is the Megaways mechanic. Instead of having reels with a fixed number of symbols, Megaways slots can have any number of symbols. 

There are columns instead of reels, and each column can show between 2 and 7 symbols. There can be more symbols, but as a standard, seven is the most. Extra belts or bonus spaces for symbols can also be implemented. 

The crux of this mechanic is that the number of ways a player can win will change for each spin. There are no complex paylines, so all you need to win is the same symbols on adjacent columns. 

Cluster Pays 

Cluster pays is a mechanic that can be used on slots with reels, but it’s more commonly found in grids. These are slots where there are no reels, but rather something like a 5×5 grid of symbols. To win with cluster pays, you need to have a cluster of the same symbols. 

Typically, the symbols need to be connected horizontally or vertically. Then again, where on the grid this happens doesn’t matter. 

The important thing is to have a cluster of the minimum number of symbols to get a win. This number is usually anything between five and eight. The more symbols you have in a cluster, the bigger the win will be.

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Win Anywhere

Win anywhere is almost like the upgraded version of cluster pays. To win on a slot with the win anywhere mechanic, it won’t matter where the symbols land. The only thing you need is the minimum number of the same symbols on a spin. 

Usually, the number needed will be something like eight. However, each slot can have different rules. The only thing that’s for sure is that the more of the same symbols you have, the more you will win. 

When playing a win anywhere slot, you can be playing both on a grid and on reels. This mechanic works just as well on both types of slot machine. 

Progressive Slots

A progressive slot can have any of the mechanics we’ve described above. It can also be played on anything from reels to columns and grids. The layout and paylines are not what makes a progressive slot. 

What a progressive slot does is that it has a form of memory. In normal slots, each game round is completely independent, and nothing from a specific spin will impact further gameplay. That’s mostly true for a progressive slot as well, except for one thing – the thing you collect. 

By collecting something, be it a special symbol or particular types of wins, you fill up a power bar. This can be done over hundreds of spins, so this is where the memory of the game comes in. Once the bar is filled, you’ll get a special bonus feature or game. 

Typically, the bonus you get from filling the bar will be a better bonus than what the game normally offers. As such, progressive slots are designed to encourage you to keep playing to trigger this extra bonus.

Bonus Buy

The bonus round in any slot is usually what players are after. This is where you’ll normally find the biggest wins in the slot game. Be it free spins or any other kind of bonus, you’ll have the chance to win big.

A new kind of mechanic in slots now is that you don’t have to wait to trigger the bonus game. If you wish, you can buy it, and this will cost you anything from 60x to 200x your bet, depending on how volatile the game is and the winning potential for a bonus round. 

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Playing Slots for Free and for Real Money

Real-money slots are available at all online casinos, and some also offer free games. Many players prefer staring off by playing in fun mode, so they can test the game. This way, you won’t have to risk your own money before you’re sure you like the slot. 

Once you’ve found a slot you like with some winning potential, you can change to real money play. Typically, this can be done by toggling a button or logging in to your account.

You can also be sure that the winning chances you have when playing in free mode are fair. Before, casinos used to up their game return to player (RTP) percentage in demo mode and then lower it in real money mode. 

Luckily, those days are gone, and all reputable casinos now offer the same game RTP. This gives you a realistic overview of what you can expect when you bet real money on the slot.

Slot Machine Features

There are many features in slots, and some have more than others. Here we’ll go through some of those features along with some slot terminology.


Three reels or five reels used to be the standard of both classic and video slots, but nowadays, a slot can have any number of reels. Some have even replaced the classic reels with a grid or columns where symbols simply fall down one by one. 


Paylines are the lines you need on a winning combination in order to win. You can find anything from one to several hundred paylines in a modern slot. Win all ways, cluster pay, win anywhere and megaways mechanics have replaced the classic paylines in many slots. 


The bet is your wager, and this determines how much money you bet per spin on a slot. Every slot will have a minimum and a maximum bet allowed. The minimum can be as low as 5c, although the minimum most commonly found is between 10c and 25c. The maximum can be limited at $50, or you can go as high as $5,000 depending on the slot settings.


If you find that pressing the spin button is tiresome, you can activate auto-spins. In some slots, this is also called autoplay. It allows you to choose a set number of spins to play without you having to start each game round. Some slots will even offer quick-spins or turbo-spins for even faster game rounds.


A wild symbol can replace other symbols in a game, and this gives you better winning chances. Typically, the wild can replace only standard symbols, not bonus symbols or scatters. There will often be other bonus features connected to a wild. Multipliers, expanding, re-spins and more are features wilds often have.


A scatter is a symbol that pays out regardless of where it lands. Thus, a scatter symbol not bound to a payline in order to trigger a win. Typically, you’ll need three or four of them to get a win, and that win is often a bonus game round. Scatters are commonly bonus symbols that activates free spins and other bonuses.

Free Spins

Free spins is a bonus game that can be triggered in many slots. What it does is give you free spins on the slot, usually with some other bonus. During your free spins, you may get multipliers, sticky symbols, a larger slot grid, or anything else. The purpose is to give you a greater chance to land a big win. 

Bonus Round

The most common bonus round in a slot machine is free spins, as described above. However, you can also win pick and click games, random prizes, re-spins, or sticky wins. No matter the exact bonus round game, this is a bonus feature that is supposed to give big wins. 

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Understand the Game Before Playing

Before you start playing slots online, it is a good idea to understand how slots work. This is important in order for you to implement the best strategy when playing. Of course, the most important thing is to manage your bankroll. 

In addition to understanding the mechanics of the slot, you also need to understand the RTP and the volatility. This is what we’ll dive into now. 

Understanding RTP (Return to Player)

RTP stands for return to player’, and this is the percentage number each game has. This percentage tells how large of a percentage of all bets placed on the slot are paid out as winnings. The RTP will always be below 100%. If it was 100%, it would mean the casino would lose money offering the game, but it does not mean that you’ll always lose when playing the slot. 

Most online slot machines will have an RTP between 95% and 96%, but some have more and some have less. The lower the number, the worse your long-term winning chances are. On the other hand, high RTP slots are more likely to result in long-term wins at the casino.

The reason we say “long-term” is that the RTP is calculated over millions of spins, sometimes even billions. This is why we’ll often refer to it as the theoretical RTP. 

The RTP is not a number for your chances of winning because accumulates based on everyone that plays. In order for you to win, others need to lose. It’s as simple as that because the casino will always retain its house edge in the long run. 

Due to the winnings being paid out randomly, you might get lucky and win big on a slot. If you do, it means you got more than your fair share of the RTP of the slot. This is likely to happen, but just as likely not to happen. 

When choosing which slot to play on, you should consider the RTP, but use it more as a guideline than an absolute. The magic ingredient for you to win will always be luck or the lack thereof. 

The Psychology Behind Online Slots

Online slots are simple games, all based on chance. There are no skills involved, and all players always have the same chance of winning. Yet, as simple as they may be, psychologically speaking, slot games are quite complex. 

Quick game rounds, the potential for huge wins, and the randomness of winning make slots different from other casino games. You’re led to believe that the next big win is just around the corner. This, sometimes, leads to players playing more game rounds than they intend to. 

Add to this that slots often slow down or make a show of a spin, almost yielding a win. For example, when you land two out of three symbols needed to trigger a bonus.

As a player, you’ll think that you just missed a win. In reality, the game round result was decided as soon as you hit spin, long before the reels slowed down.

The constant “almost wins” is why many players become addicted to playing slots. The psychological effect almost winning has on the brain, coupled with sometimes winning big, should not be underrated. 

Always keep in mind that slots are designed to make you want to spin just a couple more spins, time and time again.

Slot Myths and Superstitions

There are a lot of myths surrounding slots, and players tend to be a superstitious demographic. We’ll now have a look at some of the most common slot myths and player superstitions. 

Hot and Cold Slots

The idea that some slots are hot or cold and pay out accordingly is a common belief among players. However, this is just a superstition, and this belief has no roots in reality. 

Thanks to the RNG of a slot, all results are completely random. Not only that, but also, you have the same chance of winning on every single spin. The result of one spin does not affect the result the following results you get.

Think of it like rolling a die. The chance of getting a 6 is the same every time, no matter how many times you roll it. 

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Differences In How to Spin the Slots

Some players believe that you win more or less depending on how you spin the slot and that the game somehow will pay out less if it knows you’re about to spin 50 spins on it. This is also just another superstition. 

To avoid using auto-spin to not give away to the slot how many spins you’re intending to spin has no value. The slot does not pay out more or less if you spin 50 spins manually or on auto. The RNG is set to give only random results, and it does not register if the game is on auto or manual spins. 

Likewise, it won’t matter if you click to stop the spin or if you let the graphics play until they’re done. Which hand or finger you use to press the spin button is equally unimportant. These are things that do not in any way impact your winning chances. 

When to Play and When Not to Play

Many players think that there are certain times a day or month when they’re luckier than other times. This kind of ties into the belief that slots are hot or cold. Unfortunately, this is yet another belief that has no roots in reality, and there is no best time to play slots. The game will run as it’s intended to run, no matter what time of day it is. 

One thing, though, that can in one small way impact your slot game session is your own state of mind. You might play differently when you’re in some frames of mind versus others. For example, if you are stressed out, you might increase your bets or take bigger risks in high-variance slots, and if you’re more stressed out during some times in a day than others, this might impact your winning chances. 


Are Online Slots Really Fair?

Yes, as long as they run on an RNG, they are fair. Every result will be completely random, giving all players the same chance of winning. A certified RNG ensures that the slot can’t be tampered with, either by the casino or other players. 

Can I Win by Playing Online Slots?

Yes, you can definitely win playing slots, both online and at brick-and-mortar casinos. The casino will always have an edge, but players can also win. To find out what your winning chances in a slot are, check the RTP percentage. Also, don’t forget to take the slot’s volatility into account. Check out our online slots tips for more help on improving your odds.

Which Slot Mechanic Is the Best One?

There isn’t any slot mechanic that’s better than others because the mechanics are just there for entertainment. In reality, the mechanics won’t impact your long-term winning chances because only the volatility and the RTP can impact that. However, the most popular slot mechanics nowadays are megaways and win anywhere.

Should I Play High Volatility Games?

High-volatility games are good for certain player segments. Typically, high rollers play high volatility games because while the risk of the games is quite high, so are the chances of big wins. However, even casual players that are not too risk-averse tend to love these online casino games. 

How Long Memory Does a Progressive Slot Have?

It differs how long a progressive slot will keep your game history. There are slots that will only keep the progress for a day, while others keep it for several years. Just keep in mind that the progress is only saved at one casino. You can’t start playing the game at one casino and pick it up at another casino later. 

What Is the RTP In Slot Machines?

The standard for a slot RTP is somewhere between 95% and 96%, but you’ll find both higher and lower RTP percentages as well. Typically, the RTP is higher at an online casino app than on slots at physical casino establishments. You can usually find the specific RTP of the game listed within the game information. 

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