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Slot Machines Odds

S. Stoynova (editor) |

An In-depth Look into the Algorithms of Slot Games

Slot Machines OddsBeing one of the simplest casino games of all times, slots lure millions of recreational players with the promise of quick and lucrative payouts. And indeed, this type of game is simple to learn and play as it is based entirely on luck – there is nothing players can do to affect the outcome of the reels’ spin. However, seasoned slot fans know better. Slots are one of the most dynamic games to play in online or land-based casinos. Sure, you can potentially hit a massive payout, but you may also end up losing money at a shockingly rapid pace.

While the outcome is indeed governed by a random principle, players have greater chances of ending their betting session on profit as long as they make informed decisions when choosing which slot to play. Several things need to be factored into the equation. These include the slot’s house edge and average player return, its payouts, and volatility. When combined with good bankroll management, the proper understanding of these three factors can greatly improve your profitability. As they can be difficult for novices to grasp, however, this article aims to explain how they work and just how important they are.

Random Number Generators and House Edge in Online Slots

Random Number Generators and House Edge in Online SlotsIn online slots, the outcome of each spin is determined by programs, known as Random Number Generators. The RNG runs on complex algorithms and generates thousands of long number sequences each and every second on the basis of a predetermined formula. Each random number sequence corresponds to particular stops on the reels. From this, it follows that each spin’s outcome is completely random and depends on which number sequence the RNG will generate at the very moment a player presses the Spin button.

The sequence usually starts with what they call a seed number. Subsequent random numbers are generated on the basis of this seed, using an algorithm that only the programmer of the RNG is familiar with. The sequences of numbers are indeed long as they often consist of over 200,000 digits. Each following number in the sequence is used to generate yet another number, which itself becomes a seed. This process goes on and on even when no one is there to play the slot.

When the player hits the Spin button, the reels on the screen start rotating but the outcome has already been decided by the RNG in advance. Practically, whether you win or lose depends solely on which number sequence has been produced at the exact split second you have pressed the button. Thousands of winning and losing combinations are generated each and every instant.

How does this relate to the house edge? While random, the RNG is pre-programed to pay a specific percentage of all bets on the slot back to the players. This is referred to as the average Return to Player Percentage or RTP.

RTP is directly correlated to the house edge or the built-in advantage the casino holds over its players.

Online Slots and Player Return Percentages

Online Slots and Player Return PercentagesThe average return will vary, depending on the slot title and the software developer, which has supplied the casino with the game. Payout percentages typically vary between 86% and 99.9%. The higher the coin denomination of a given slot is, the higher its average payout percentage would be. Slots with smaller coin denominations are typically on the lower end of the scale, which is to say players should probably steer clear of playing those.

The house edge in slots, especially when multiple paylines are involved, would be next to impossible to calculate using formulas, especially by the average player. The good news is it is directly related to the average player return percentage, which renders it possible for players to calculate the casino’s built-in advantage without necessarily being mathematical geniuses.

Let’s demonstrate with an example, using NetEnt’s Jack and the Beanstalk for the purpose. The average return to player percentage for this slot stands at 96.30%. You can calculate the house edge by subtracting the slot’s RTP from 100%. From this, it follows that Jack and the Beanstalk’s house edge is set to 3.70%. This practically means that the house collects $3.70 on average per every $100 wagered on this slot.

At this point, you are probably wondering “Why play slots at all if the games are always tilted against me?”. And rightfully so. The truth of the matter is while accurate, both the house edge and the RTP even out to 3.70% and 96.30%, respectively, over extremely long periods of time. Realistically speaking, you cannot expect to collect $96.30 per every $100 you wager on Jack and the Beanstalk.

It will take hundreds, and even thousands of hits of the spin button until the RTP and the house edge even out to the percentages, specified by the casino. The average player return is calculated over millions of spins for a given slot machine. If you collect a payout of $2.20 with an initial stake of $0.75, you are not simply getting your original bet back in addition to your net profit, you are practically getting $0.75 from another slot player who failed to win on their spin. From this, it follows that the more you bet on any given slot, the closer you will get to the average player return percentage, listed in the slot’s paytable.

It goes without saying, players should always check what the average return on a given slot is before they proceed with placing their bets. Common sense dictates that one should opt for betting on slots where the RTP is higher and therefore, the house edge is lower. It would be best to choose slots where the average return exceeds 95% or 96%. However, a high return percentage does not necessarily mean the slot would spew back payouts all the time. This is where volatility, also known as variance, comes into play.

Difference between Return Percentages and Hit Frequency

DifferenceSlot novices sometimes assume hit frequency is the same as return percentage but the two concepts are entirely different. Let’s demonstrate the difference with an example, using two hypothetical slot games for the purpose. The reel stops contain blanks along with symbols but both games pay only on condition the player gets three matches on the single payline.

The odds are adjusted in such a way so that the game produces 10,000 possible symbol combinations in total. The table below shows you how many winning combinations the two made-up single-line slots can produce and their respective payouts.

Symbol CombinationPayoutSlot 1 Combination Hits per 10,000 SpinsSlot 2 Combination Hits per 10,000 Spins
3 x bells800 to 111
3 x lucky 7s80 to 14545
3 x cherries10 to 1350350
3 x lemons2 to 1700995
No matchesNo pay8,9048,609

Based on this paytable, we can see that Slot 2 yields 1,391 winning combinations as opposed to Slot 1 where the paying combinations are only 1,096. It follows that Slot 2 has a hit frequency of 13.91%, whereas that of Slot 1 is only 10.96%. Both games have the same hit frequency and payouts for combinations of three bells, lucky 7s, and cherries.

Slot 2 has a better hit frequency and greater theoretical return than Slot 1

The lowest paying combination with the three lemons on Slot 2 hits 295 times more often compared to Slot 1. In turn, this results in Slot 2 having a better hit frequency and theoretical return percentage. For every 10,000 credits played, both games pay 800 coins for bells, 3,600 coins for lucky 7s, and 3,500 coins for the cherries. Therefore, the overall return for these combinations is 7,900 coins in both games. The difference comes from the discrepancy in the low spectrum of the paytable.

3 x lemons hit less frequently on Slot 1, which lowers its theoretical return

Slot 1 pays 1,400 coins for the lemons, whereas Slot 2’s return for this combination is higher with 1,990 coins. The discrepancy leads to a theoretical return of 9,300 coins (93.00%) for Slot 1 and 9,890 coins (98.90%) for Slot 2. The bottom line is the two games would appear the same if you see them on the casino floor next to each other. They both share the same winning combinations and payouts. It would be impossible for you to tell Slot 2 has a better hit frequency and greater theoretical return than Slot 1.

Slot developers can increase or decrease a game’s RTP by changing the paytable

A slot manufacturer can design a game with the hit frequency of Slot 1 and the return percentage of Slot 2, and vice versa. The easiest way to achieve this is by changing the paytable. Let’s assume the two slots’ hit frequencies remain 10.96% and 13.91%. However, the manufacturer decides to boost the payouts for lucky 7s from 80 to 95 coins on Slot 1 and reduce them from 80 to 70 on Slot 2.

A slot with a greater hit frequency can have a lower return than one with a worse hit frequency

Slot 2’s hit frequency would still be higher but Slot 1’s theoretical return would increase from 93% to 99.75%. In the meantime, the long-term payout percentage of Slot 2 would drop from 98.90% to 94.40% despite the fact it still has a higher hit frequency than Slot 1. To wrap things up, our point is to demonstrate that a better hit frequency does not necessarily mean a better return percentage. This is because hit frequency denotes the percentage of spins that yield payouts, whereas the RTP reflects the percentage of bets returned as player profits.

Figuring Out the Odds of Slots

Figuring Out the Odds of SlotsCalculating the odds (i.e. the probability) of hitting the maximum payout on a classic, 3-reel slot is relatively simple as there is typically a single combination of symbols on the reels that pays out the jackpot. It all depends on the number of symbols (referred to as “stops”) and the number of reels the game utilizes.

If there are three reels, with each containing 16 different symbols, the odds of hitting the maximum payout can be represented in the following way – 1/16 x 1/16 x 1/16, which equals 1 in 4096. It is possible to calculate the probability of hitting any symbol combination on the three reels by using this method.

But the outcome of the spins on more advanced video slots is determined by the aforementioned RNGs. Such slots typically have five reels and multiple paylines, with a far greater number of symbols. Needless to say, this would render the calculation of the odds of landing specific combinations extremely difficult. A five-reel slot with 32 symbols can render more than 3 million combinations.

Then again, most advanced video slots have over 200 stops per reel, so obviously calculating the number of possible combinations would be next to impossible.

Low and High Volatility in Slots

Low and High Volatility in SlotsPrior to committing with any real-money wagers, slots novices should acquaint themselves with what the terms volatility and variance stand for. The two terms are often used interchangeably as they practically mean the same thing. Volatility refers to the inherent risk of the slot or in other words, how often and how much money players can expect to collect at the end of their gaming session.

Thus, slots can be divided into two main categories – slots with low and slots with high volatility. Games with higher volatility involve a higher degree of risk for the players. Such slots typically offer better payouts but the winning combinations tend to occur far less frequently. But when they do pay, higher-volatility slots pay big. These are a suitable option for patient players with more substantial bankrolls, which would see them through until they succeed in hitting a lucrative payout. Also, there is usually not much action in such games.

From this, it follows that slots with low volatility come with less inherent risk for the players. On low-volatility slots, players tend to land winning combinations more often, but the payouts are far from life-changing. However, such games are action-packed so one will hardly ever grow bored with playing. It is precisely their bonus features that keep enthusiasts entertained for prolonged periods of time. Low-volatility slots are considered a suitable option for players on a budget, who are betting primarily for entertainment and wish to extend their gaming session as long as possible.

Unlike the average player return, the volatility of slots is not listed in the paytable as casinos usually refrain from providing such information to their players. Despite that, the paytable may be used as an indicator of whether a specific slot comes with high or low volatility. If the paytable of your preferred slot offers you a maximum payout of half a million coins, the game’s volatility is probably medium to high. The more lucrative the payouts in the paytable are, the higher the slot’s volatility.

Another thing you can do is compare the payouts for landing a four-of-a-kind (combination with four identical symbols on the reels) with those of hitting a five-of-a-kind combination. If the difference between the two is 5x or less, the slot’s volatility is probably low. However, if the difference in the payouts for the highest paying symbol combinations exceeds 10x, you are most certainly looking at a high-volatility slot.

Example of High Volatility Slot: Gems Bonanza

In the realm of high volatility slots, Gems Bonanza by Pragmatic Play truly sparkles. This isn’t your garden-variety slot game, as it spreads across a vibrant 8×8 grid where every spin could lead to a dazzling win, especially with a max payout that can multiply your stake by up to 10,000 times!

Gems Bonanza

Screenshot of Gems Bonanza

Gems Bonanza Overview
TitleGems Bonanza
DeveloperPragmatic Play
Layout8 reels, 8 rows
PaylinesCluster Pays
Min/Max Bet0.20/100 
Release DateOctober 29, 2020

Gems Bonanza is a cluster-pay video slot that offers an adventure through a grid of precious stones, with each spin holding the potential to trigger a chain reaction of wins. The game’s high volatility means payouts might not come as often, but when they do, they can be massive, thanks to features like the Gold Fever Progressive and various spin modifiers.

Whether you’re a high roller or just testing the waters, Gems Bonanza’s broad betting range makes it accessible for all players. With its combination of eye-catching graphics, engaging features, and the thrill of chasing those high payouts, this slot is a gem worth spinning.

Starburst: The Low Volatility Legend

Starburst by NetEnt is the poster child for low volatility slots, a true classic that’s been a player favorite since its release in 2012. Its space-themed adventure brings a calm yet captivating experience across 5 reels and 10 paylines. With the chance to win both ways and the Starburst symbol triggering up to three ReSpins, this slot promises steady action without the risk of meteoric losses accumulating in no time.

Starburst: The Low Volatility Legend

Screenshot of Starburst

Starburst at a Glance:
Layout5 reels, 3 rows
Min/Max Bet0.10/100
Release Date2012

Starburst stands out for its simplicity and dazzling gameplay, complete with vibrant gems and nostalgic symbols like the lucky ‘7’ and the BAR. The Both-Way wins mechanic doubles your chances for a win, and the low volatility means you’ll enjoy frequent small wins, perfect for stretching out the fun without breaking the bank. It’s a cosmic journey with gentle thrills, ideal for both new players and those looking for a serene slot 


The outcome of each spin is determined by a Random Number Generator (RNG), ensuring each spin is completely independent and random. The RNG generates thousands of number sequences per second, making each spin’s outcome unpredictable and unrelated to previous or subsequent spins.

The house edge in slot machines is directly related to the Return to Player (RTP) percentage. It represents the casino’s average profit from a player’s bet. For example, a slot with an RTP of 96% has a house edge of 4%, meaning the casino expects to make an average profit of 4% over the long run.

Yes, choosing slots with higher RTPs can improve your chances of winning in the long run. Slots with an RTP of 95% or higher offer better potential returns to the player compared to titles that have lower RTP rates. Playing a slot with a higher RTP will reduce the house edge and will increase your chances of ending a session profitably.

Volatility refers to the risk and payout frequency of a slot, with high volatility offering larger but less frequent wins, and low volatility offering more frequent wins that are, however, significantly smaller in size. RTP, or Return to Player, indicates the average percentage of bets that are returned to players over time, regardless of volatility. Simply put, the volatility of a slot indicates the risk level, while the RTP shows what return you can expect in the long run.

While casinos don’t typically list a slot’s volatility, you can infer it by looking at the paytable. Slots with larger maximum payouts are likely to have high volatility, while those with smaller maximum payouts but more frequent winning combinations have low volatility. The difference in payouts for four-of-a-kind versus five-of-a-kind can also indicate volatility, with way too big of a difference indicating high volatility.

No, slots do not pay out more at certain times of the day. The RNG technology ensures that each spin is entirely random, making the odds of winning the same at any time. Player traffic may vary, but it does not influence the slot machine’s payout rates.

No, it is not possible to predict when a slot machine will hit a jackpot because of the randomness introduced by the RNG. Each spin is independent and has the same chance of winning the jackpot as any other spin, regardless of previous outcomes or how long the machine has been played.