How slot machines work in online casinos

More and more users prefer online gambling as a form of recreation. Online slots are popular among them. Understanding the principle of operation of slot machines on the Internet will allow you to stay in the black.


The general principle of operation of any slot machine. How the pseudo random number generator works in slot machines. Slot machine math. How the manufacturer sets up the software. What is the difference between slots in online casinos. The general principle of operation of any slot machine
All slots use approximately the same mechanics. The apparatus consists of drums that generally rotate vertically. They are marked with prize and special symbols. Several rows are displayed on the playing field at the same time. If allowed, the player chooses the number of active lines.

Slot machines in casinos work according to this principle
Slot machines in casinos work according to this principle

The reels start to move after pressing the Spin button. After the stop, the prize combinations are checked in accordance with the paytable. Basically, wins are given for a sequence of identical symbols, starting from the left reel. However, there are slots in which prize combinations are also formed from the right edge of the playing field or in clusters, regardless of position. Winnings for all lines are summed up. The prize amount can be immediately sent to the balance. Many machines offer a chance to increase the money received in the risk game. Each successful attempt doubles the amount. In case of loss, the money is burned. Online slot machines may offer bonus features. They are launched, for example, after the required number of scatters appears. These can be both free spins and re-spins, and bonus rounds. There are also paid options. For example, in some slots it is offered to buy bonuses.

How the pseudo random number generator works in slot machines
A special program is often used to generate results in online slots. This is the so-called pseudo-random number generator or PRNG for short. It is created by the developers who release the game.

To generate the results, the PRNG generates base numbers according to a specific algorithm. To prevent it from being hacked, random values ​​are periodically added to the sequence. The pseudo random number generator generates them even before the spin starts. However, they are displayed on the screen as game symbols only after the reels have stopped. PRNG also takes into account bonus features, including free spins.

Slot machine math

The creation of an online device begins with the development of its mathematical model. She is the skeleton of the future game. It contains:

  • RTP return rate.
  • Dispersion.
  • Winning frequency.
  • The amount of payments.
  • Only when the mathematicians approve the model do designers and programmers get to work.

How to calculate the real payout percentage can be seen on the example of slot 777. Its design consists of 3 reels, each of which contains 20 game symbols. To begin with, a paytable is written taking into account all possible sequences of symbols.

Payouts by prize combinations

Next, it is recorded how many times this or that symbol can appear on each reel. For example, 7 occurs once. Cherries fall out on the first reel in 2 cases, on the second in 6 cases, and never on the third. At the bottom, the total result of dropping symbols is calculated.

Slot machines in casinos work according to this principle
Slot machines in casinos work according to this principle

At the next stage, the number of cases when this or that combination can fall out is determined. To do this, you need to multiply the results from 3 columns. Combination 777 can be dropped only 1 time (1x1x1). Two watermelons and one inscription Bar in one line meet 4 times (2x2x1). How many times does the winning combination appear on the machine? Now you need to calculate the total payout for the combination. To do this, the number of cases determined at the previous stage is multiplied by the amount of remuneration from the machine’s table. For the 777, the return will be 200 credits. This amount is obtained for one possible combination, for which 200 coins are paid. At the same time, for 3 watermelons, the total return will be 800 credits (8×100).

Next, the number of options is determined when the sequences of symbols bring payouts. In this example, that number is 1073. The total refunds are also determined, which is 7,556 credits.

Total number of prize combinations

Since each reel has 20 symbols, the total number of prize and unpaid combinations is 20x20x20 = 8000. Then the probability of a winning sequence will be 1073/8000 = 13.41%. The established RTP is 7556/8000 = 94.45%. Let’s consider what they are and how they differ from each other. If you are still looking for a good casino, then you should try this site –

Slot machines in casinos work according to this principle. This is the simplest example. With the addition of the number of reels, bonus lines, wilds, scatters, bonus functions, the mathematical model becomes much more complicated. Only the developer owns the real calculations.