Slot Machine Probability

Slot Machine Probability

Gambling is attractive because you never know for sure what the result will be, whether you will win or lose. This is especially true for slot machines because they do not have complicated strategies or methods of mathematical analysis. When you spin the reels, you can both lose a bet and receive a large payout thousands of times more than the spin value. Let’s discuss slot machine probability for USA players and what it depends on.

Slot Machine Work Explained

Slots are games with one of the simplest operating principles, as they have a minimum entry threshold for players and allow you to make bets without skills or special knowledge. Even if you do not know particular slot machine mechanics and what it pays for, it does not reduce your chances of winning, as it all depends on luck.

Slot machines do not require learning the rules and mastering strategies, so even newbies in online casinos can play them.

After starting a particular slot, all you need to do is to determine the bet size, and you can start making spins right away. Successful spins bring various prizes, and unsuccessful ones lead to losses, so you do not have to make complex decisions, learn strategies, or think about what bet is the best right now: just make spins and watch your results.

Slot Machine Probability & Math Basics

Slot machines use simple mathematics to determine spin results, so in most cases, you can calculate probabilities manually.

Odds of Winning in Slot Machines

To calculate the odds of winning in a particular slot machine, you need to multiply by each other the total number of symbols that can appear in each playing field cell. For example, if the slot has 8 symbols, one row, and three reels, the total number of combinations is 8 x 8 x 8 = 512. Then divide the number of winning sequences by this number to get the exact odds.

Random Number Generator

To calculate the probability of slot machines, you should consider a random number generator work, as only RNG is responsible for the results. When you set the reels in motion, the algorithm performs complex mathematical calculations and generates a random combination of symbols on the playing field. Due to the RNG operation, results are completely unpredictable, and the previous spins have no effect on future ones.

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Average Payouts & RTP

Each slot machine has a particular RTP value, which determines the theoretical return-to-player percentage; in fact, this criterion reflects your chances of winning.

Gambling providers set RTP values while creating licensed slot games; online casinos and players cannot influence or change it.

The average payout is also a valuable indicator for determining the odds of winning since each game uses different prize multipliers. The basic formulas work as long as the minimum payout is equal to or greater than your initial bet.

Understanding House Edge

Every casino table game has a specific house edge described in the rules. This criterion allows gambling venues to make a profit in the long run, regardless of individual players’ results.

House edge in roulette
Zero provides the house edge in roulette

Despite this, you can still increase your chances of winning using various tactics. There are many strategies for blackjack, roulette, poker, and several other table games that can make your gambling more successful and profitable. Most use statistical and mathematical analysis, as well as the theory of probability, as a basis, but you can choose any tactics you want in each specific situation, but remember that not all are equally profitable.

What Affects the Probability

The chances of winning depend on many factors. Let’s take a look at the most important ones.

Number of reels and rowsThe total number of cells on the playing field
Number of winning linesThe number of ways to form winning combinations
SymbolsThe number of unique symbols available in the slot
Payout multipliersThe prize ratios assigned to each symbol

It is also essential to consider the availability of additional mechanics and features: wilds, scatters, multipliers, free spins, re-spins, bonus rounds, jackpots, and so on.

How to Calculate the Probability of Slot Machines

There is a slot machine probability formula for USA users, which allows anyone to calculate the probability of winning. To make it more understandable, let’s imagine a slot with one payline and a one-coin bet that also has three reels and one row with six symbols, giving 216 ways to win. The highest-paying image is a diamond, and the other symbols are fruits.

There are 4 conditions you need to meet to receive a payout:

  • Three diamonds — 30 coins. The probability is 1 to 216.
  • Three fruits — 10 coins. The probability is 5 to 216.
  • Two diamonds — 4 coins. The probability is 15 to 216.
  • One diamond — 1 coin. The probability is 75 to 216.

The probability of winning in such a slot can be calculated by the following formula: (30 х 1 + 10 х 5 + 4 х 15 + 1 х 75) / 216 = 99.54%.

Slot Machine Probability Problems

Although it is possible to calculate the odds of winning in any slot machine, it can be quite difficult in reality. As an example above, we considered the most simple game with only three reels and one payline, but such slot machines are pretty rare at modern gambling venues. Usually, there are many more lines and rows, and besides prizes for forming combinations of identical symbols, there are various additional mechanics.

Probability of winning in slots
The vast majority of slots have more than one row and one payline

As a striking example of slot machine probability problems in terms of calculating the odds, you can consider any game with the Megaways mechanics. The number of paylines can be hundreds of thousands, so it is almost impossible to calculate the odds manually; for sure, you can try doing this, but it would take a ton of time.

Casino Strategies With Probability Basics

Since spin results do not affect each other, and a random number generator is responsible for determining outcomes, it makes no sense to use strategies in slots even if you have calculated the odds precisely.

We absolutely do not recommend using strategies with a geometric progression of bet size, such as Martingale. Its application only leads to the risk of losing your bankroll in a few minutes.

Best Tips to Play Slots

Instead of using strategies, it is better to adhere to a few valuable tips that can help reduce the risks and, accordingly, increase the chances of staying in the black:

  • Choose slots with the highest possible RTP level.
  • If you have a small bankroll, give preference to games with low volatility.
  • Divide your bankroll by at least 70-80 bets.
  • Do not increase the bet size to win back for losses.
  • Stop gambling after receiving a large payout.

Remember that gambling always involves risks, so never play with money you are not prepared to lose and control your emotions.

Probability of Winning Slots vs Table Games

You can calculate the probabilities of winning both for slot machines and table games, but it is much easier to do it with table games because the total number of possible outcomes is noticeably lower. For example, to determine the probability of a particular number coming up on the roulette wheel, you need to divide one number by the total number of sectors and then multiply the result by 100. So, in European roulette, the probability of a particular number coming up is 2.7%. If you prefer less risky bets, for example, bets for equal odds, the likelihood of winning reaches 48.64%.

The odds of winning during a single spin are noticeably lower in slots, but the potential payouts are much more significant. If you compare roulette with an average slot machine, in the first case, the maximum payout you can count on is 35 to 1, and in the second case, they can exceed your bet by thousands of times. Of course, it happens rarely, but there is always a slight chance.

We cannot say that table games are better than slots or vice versa, as these games are completely different, with probabilities of a different nature.


Since the odds in each slot are calculated individually and with dozens of variables, such calculators make no sense.

This figure varies greatly and can be either 92% or 98%, but most slots have RTP between 94% and 97%.

Use the Help section or the provider’s website to clarify this question.

No. Desktop and mobile versions of slot machines differ only in terms of the interface.

This is a particular sequence of identical symbols you need to form to get the prize money.

Publication Author
Donald Peterson
Author of articles
Donald Peterson is an avid gambler from Edmonton, Alberta, who also writes about his experience with casinos. He’s been in the business for over 10 years, following the ever-changing industry landscape. His articles are aimed at helping beginners with choosing casinos, suitable games, and strategies.
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