How slot machines work
A slot machine picks a random stop for every reel the moment you press Spin, then pays by its pay table.
One spin, step by step
- You press Spin.
- The random number generator (RNG) picks one stop for each reel at that instant.
- The machine reads the symbols at those stops and checks every active payline.
- It pays whatever the pay table says for those symbols.
Online slots work the same way – the RNG is software on a server, and the reels on screen are a picture of its pick.
Reel strips: fixed stops, set symbols
| Symbol | Reel 1 | Reel 2 | Reel 3 |
|---|---|---|---|
| X | 9 of 28 | 9 of 28 | 9 of 28 |
| BAR1 | 5 of 28 | 5 of 28 | 5 of 28 |
| W | 1 of 28 | 1 of 28 | 1 of 28 |
| BAR3 | 3 of 28 | 3 of 28 | 3 of 28 |
| CH | 4 of 28 | 4 of 28 | 4 of 28 |
| BAR2 | 4 of 28 | 4 of 28 | 4 of 28 |
| S7 | 2 of 28 | 2 of 28 | 2 of 28 |
Sapphire Sevens: how many stops each symbol has on each reel. Rare symbols pay more.
Each reel has a fixed number of stops, and each symbol fills a set number of them. On Sapphire Sevens (classic three reels, one line), the seven sits on few stops, so three sevens line up rarely.
All its reels together make 21,952 stop combinations, and the RNG treats each one the same.
Paylines: where a win counts
| Symbol | Reel 1 | Reel 2 | Reel 3 | Reel 4 | Reel 5 |
|---|---|---|---|---|---|
| J | 5 of 26 | 5 of 26 | 5 of 26 | 5 of 26 | 5 of 26 |
| Q | 4 of 26 | 4 of 26 | 4 of 26 | 4 of 26 | 4 of 26 |
| GEM | 2 of 26 | 2 of 26 | 2 of 26 | 2 of 26 | 2 of 26 |
| W | 1 of 26 | 1 of 26 | 1 of 26 | 1 of 26 | 1 of 26 |
| K | 4 of 26 | 4 of 26 | 4 of 26 | 4 of 26 | 4 of 26 |
| A | 4 of 26 | 4 of 26 | 4 of 26 | 4 of 26 | 4 of 26 |
| BELL | 3 of 26 | 3 of 26 | 3 of 26 | 3 of 26 | 3 of 26 |
| STAR | 3 of 26 | 3 of 26 | 3 of 26 | 3 of 26 | 3 of 26 |
Brass Bells: how many stops each symbol has on each reel. Rare symbols pay more.
Brass Bells has five reels and ten lines, giving 11,881,376 stop combinations. A win counts only when matching symbols land on an active payline, starting from the left reel.
Example: three bells on line one pay; the same three bells split across different lines pay nothing.
Reel strips and the pay table decide the RTP
| Slot | Return (RTP) | A win every | Volatility (SD) | Top win (bets) |
|---|---|---|---|---|
| Sapphire Sevens classic 3 reels, 1 line, low volatility | 95.93% | 4.1 spins | 5.18 | 400 |
| Brass Bells 5 reels, 10 lines, low volatility | 96.15% | 3.1 spins | 2.96 | 267 |
| Midnight Sequins 5 reels, 10 lines, high volatility | 95.98% | 4.4 spins | 7.83 | 1266 |
Exact numbers from every possible reel stop. These are our own teaching slots; real casino slots set their own numbers.
Add up the payout for every stop combination and divide by the number of combinations, and you get the return to player (RTP). Brass Bells returns 96.15% of all bets over time – an average loss of $3.85 per hundred dollars bet.
Same idea, different feel: Brass Bells pays on about 1 in 3.1 spins (low volatility), while Midnight Sequins pays less often but can hit 1266 times the bet (high volatility). Real casino slots have their own numbers, set by the game maker and the casino – see slot RTP.
The animation and near misses
The result is fixed the moment you press Spin – the spinning reels only show it, and stopping them early changes nothing.
A near miss – two sevens and the third just above the line – is one ordinary combination out of many. It does not make the next spin closer to a win, because every spin is new (see the gambler's fallacy and are slots rigged).
Questions
How are slot machines programmed?
The game maker sets the reel strips, the symbol counts on each strip and the pay table. Those three things fix the RTP, and a random number generator picks the stops on every spin.
How do online slots work?
An online slot uses a software random number generator to pick a stop for each reel when you press Spin. The reels on screen are an animation that shows the result already chosen.
Does a near miss mean a slot is about to pay?
No. A near miss is just one of the possible combinations, and each spin is independent of the one before.
Can you tell when a slot machine will hit?
No. Every spin is a new random pick, and over time the house edge tends to take its share of the total amount bet.