What Happens When You Press Spin
A spin takes only a few seconds, but several steps happen in that time.
1. Your bet is placed. The amount you have chosen to stake is deducted from your credit balance.
2. A random number is selected. The game's random number generator is constantly producing numbers, even when nobody is playing. The number (or set of numbers) drawn at the moment you press spin decides the outcome.
3. The number is converted into reel positions. The game's software maps the random number to a stopping position on each reel.
4. The result is checked against the paytable. The game works out whether the symbols that landed form any winning combinations or trigger any features.
5. The animation plays. The reels spin and stop to show the result that has already been decided.
6. Any winnings are paid. If you have won, the amount is added to your credit balance.
Because the result is fixed at step 2, nothing you do after pressing spin changes it. Stopping the reels early with a button or tap only skips the animation.
The Random Number Generator
The random number generator is the heart of every modern pokie. It is a piece of software that produces long sequences of numbers with no predictable pattern.
Most games use a pseudorandom number generator, which uses a mathematical formula to produce numbers that behave randomly for all practical purposes. These generators are tested by independent laboratories to make sure the results are unpredictable and evenly distributed over time.
Two important consequences follow from this:
- Every spin is independent. The game has no memory of previous spins. A machine is never "due" to pay out, and a big win does not make the next spin less likely to win.
- Timing does not matter. Because the RNG produces numbers continuously and at high speed, it is not possible for a player to time a spin to land a particular result.
Our Slot RNG Explained guide covers random number generators in more detail.
Reels, Virtual Reels and Symbol Weighting
On early mechanical machines, each reel had a fixed number of physical stops, and every stop was equally likely. This limited the size of the prizes that could be offered.
In the 1980s, Norwegian mathematician Inge Telnaes patented a system that used a random number generator to select reel stops from a "virtual reel". A virtual reel can have many more positions than the visible reel, and each visible symbol can be assigned to several virtual positions or just one. This is known as symbol weighting.
Weighting means that different symbols can have different chances of landing, even if they appear the same number of times on the visible reel strip. Low-paying symbols are typically given more positions and high-paying symbols fewer. This is how games can offer very large prizes with very small chances of winning them.
Modern video slots often have long reel strips with many symbols on each reel, and their designers set the frequency of each symbol to achieve the game's intended maths. Either way, the principle is the same: the chance of each symbol landing is set by the game design, not by what you see on screen.
How the Maths of a Pokie Is Built
Every pokie is built around a mathematical model that decides how it pays over time. Three figures describe that model.
Return to Player (RTP)
RTP is the percentage of all money wagered that a game is designed to pay back over a very large number of spins. If a game has an RTP of 96%, it is designed to return $96 for every $100 wagered across millions of spins. The remaining 4% is the house edge. RTP does not predict what will happen in a single session. Read Pokies RTP Explained and RTP vs Actual Slot Results for more.
Hit Frequency
Hit frequency is how often a spin produces any win, regardless of size. A game with a hit frequency of 25% produces a win on roughly one spin in four over the long term. Many of those wins may be smaller than the original bet.
Volatility
Volatility describes how a game's payouts are spread out. Low-volatility games tend to pay smaller wins more often, while high-volatility games pay less often but can produce much larger wins. Our Slot Volatility Explained guide explains the difference.
Game designers balance these figures by deciding how often each symbol and feature appears and how much each combination pays. Bonus features, such as free spins and multipliers, usually account for a significant share of a game's total return.
How Wins Are Calculated
Once the reels stop, the game checks the result against its rules. How it does this depends on the game type:
- Payline games pay for matching symbols along set lines across the reels, usually from left to right. See Slot Paylines Explained.
- Ways to win games pay for matching symbols on adjacent reels in any position. See Ways to Win Slots Explained.
- Megaways games use reels that change height on each spin, changing the number of ways to win. See Megaways Slots Explained.
- Cluster pays games pay for groups of touching symbols. See Cluster Pays Explained.
Special symbols can change the result. Wild symbols substitute for others, and scatter symbols usually trigger features wherever they land. The paytable explains exactly how each game works.
From Mechanical Reels to Video Screens
Slot machines have changed a great deal since the first coin-operated machines of the 1890s.
- Mechanical machines used physical reels, springs and levers. The pull of the lever set the reels spinning, which is where the nickname "one-armed bandit" comes from.
- Electromechanical machines arrived in the 1960s. Bally's Money Honey, released in 1963, could pay out large numbers of coins automatically from a bottomless hopper.
- Video slots replaced physical reels with a screen. The first was developed by the Fortune Coin company in 1976, using a modified television display.
- Online slots brought the same technology to computers and phones, with game results generated by the RNG on the game provider's servers.
Today, many venue pokies in Australia are also connected to monitoring systems that record activity and help regulators oversee the machines.
How Pokies Are Tested and Regulated
Before a pokie can be installed in an Australian venue, it must be approved by the relevant state or territory regulator. Machines must meet technical standards, including the Australian/New Zealand Gaming Machine National Standard and local requirements, which cover areas such as the RNG, game rules, displays and minimum return to player. Minimum return requirements vary between states and territories.
Independent testing laboratories check that each game's RNG produces unpredictable results and that the game pays out in line with its published maths. Online slots are tested in a similar way for the markets in which they are licensed. You can find out more about the studios behind the games in our Slot Game Providers section.
What This Means for Players
Understanding how slot machines work helps set realistic expectations:
- Every spin is random and independent. No pattern, timing or system can change the result.
- The house edge means players as a group lose money over time.
- RTP and volatility describe long-term behaviour, not what will happen today.
- The speed of play means money can be spent quickly, even at small stakes.
If you choose to play, set a budget and a time limit first and never chase losses. Our guides on setting gambling limits and recognising gambling harm can help, and Gambling Help Online offers free, confidential support 24/7 on 1800 858 858.