How a slot machine's odds are set
A slot machine's return is set by its reels and pay table, written in a sheet the player never sees. Here is an example, not a real machine: three reels of 32 stops. It pays back 83.72% of what is played, so each €1 spin loses €0.16 on average. At 600 spins an hour, an hour costs about €97.71.
Change the machine
The player sees the same symbols and the same pay table. What the player does not see is how many blanks each reel holds.
Check the figures: up to 40 blanks, three 7s paying up to 2,000 times, and a starting sum of up to 200 stakes.
The machine pays back 83.72% of what is played and keeps 16.28%.
Each reel has 32 stops, so 32,768 combinations. Something pays on 20.8% of spins, and three 7s come once in 8,192 spins.
At €1.00 a spin and 600 spins an hour, an hour costs on average €97.71.
Of the players who start with €100.00, half have lost all of it within 238 spins, about 24 minutes.
The count runs in your browser and needs JavaScript. The figures here are for the machine as described.
The reels
| Symbol | Reel 1 | Reel 2 | Reel 3 |
|---|---|---|---|
| Wild | 1 | 1 | 0 |
| 7 | 1 | 1 | 1 |
| Triple bar | 3 | 3 | 3 |
| Cherry | 5 | 5 | 5 |
| Single bar | 8 | 8 | 9 |
| Blank | 14 | 14 | 14 |
The wild stands for any symbol that pays, and sits on the first two reels only.
What pays, and how often
| Line | Pays | Chance | Ways out of 32,768 | Share of the return |
|---|---|---|---|---|
| 7, 7, 7 | 1,000 | 1 in 8,192 | 4 | 12.21% |
| Triple bar, triple bar, triple bar | 100 | 1 in 683 | 48 | 14.65% |
| Cherry, cherry, cherry | 40 | 1 in 182 | 180 | 21.97% |
| Single bar, single bar, single bar | 5 | 1 in 44.95 | 729 | 11.12% |
| Cherry, cherry, any | 3 | 1 in 34.17 | 959 | 8.78% |
| Cherry, any, any | 1 | 1 in 6.67 | 4,910 | 14.98% |
For the machine as described. Each spin is paid by the first line it matches, from the top; "any" means any symbol. Pays are times the stake, and the stake is not returned on top: a cherry paying 1 just gives back what you played.
How it is worked out
Every combination of the three reels is counted, with the line it pays. The return is the sum of the pays divided by the number of combinations; no random numbers. A second, independent count by symbol type must give the same for every change you can make here, or the page is not published. How long the money lasts is worked out exactly, spin by spin, for every amount you might have left; the count stops for a player whose money reaches three times the start, or 200 stakes more if that is higher.
What this leaves out
- This is an example to show how a machine works, not a real one. Real machines have many more stops, many lines and bonus rounds, and their sheets are not published.
- Two machines that look the same can have different reels and so a different return. Only the machine's sheet says which is which.
- The 600 spins an hour are an assumption; type in your own pace.