How Slot Machines & Coin Slots Work

Slot machines are the most popular games in any casino, but a lot of people don’t have a clear understanding of how they work. In fact, some people have an out-and-out misunderstanding of how they work, while others are more than willing to take advantage of the gambling public’s ignorance in such matters. See our page about slot machine myths for about what we think of those people.

The purpose of this page is to explain in some detail how a slot machine actually works. Once you have an understanding of the actual inner workings of the game, you might find yourself less (or more) attracted to this type of game, depending on your temperament. Slots can be a lot of fun, but they’re extraordinarily profitable for the casino for several reasons, not least of which is how they actually operate.

Are Online Slots Rigged? If online slots were rigged, then you can guarantee that almost all of them would be closed down by now. It’s one of the biggest concerns people have when playing online, and it’s why we only recommend reputable casinos here at VSO. The top gaming jurisdictions such as UK, Malta and Gibraltar ensure that fair and secure gaming requirements are in place, and this gives each person the same percentage chance of winning.

Return to Player (RTP) is the factor that decides how much the slot pays out. If the slot has an RTP of 96%, then for every $100 that is gambled, the slot will payout out $96. This is regulated and independently tested to make sure you have a safe environment to play it.

We want all of our readers to make the right decisions when it comes to playing games online, so follow our recommendations and eliminate any risk of encountering rigged slots.

Slot machines use a random number generator. Early slot machines were mechanical (think coin slots), but they still used a random number generator, in the same sense that a roulette wheel, a deck of cards, or a pair of dice are also random number generators. Modern slot machines use a computer to generate random numbers, and these determine the outcomes of the game.

The important thing to remember is that the results are truly random. The game doesn’t work on any kind of cyclical basis, and slot machine jackpots don’t become due. Slots don’t get hot or cold, either. They only seem to, and only then in retrospect. It’s not something you can predict, any more than you can predict with any degree of certainty what the next card will be when dealing a deck of cards.

The casino does have an edge over the player. This is true of every casino game, in fact. The casino gets its edge using math and large numbers. Every bet on every casino game offers a lower payout than the actual odds of winning.

For example, in roulette, the odds of hitting a specific number are 37 to 1. But a bet on a specific number only pays off at 35 to 1. It doesn’t take a genius to figure out how the casino makes its profit in that situation, does it?

Slot machines work the same way.

Slots usually have three reels but sometimes also have five reels. The reel is the image that spins in the front of the machine. It has multiple symbols on it, and if you line up certain combinations of symbols, you win money. The less likely it is to line up a particular set of symbols, the higher the payout on that particular combination.

For decades, these reels were literally large metal hoops, but now that slot machines are powered by computers, they’re more often just images on a video screen. Even in the case of slot machines with actual reels, the outcome is determined by the random number generator inside the computer.

Where those reels stop are called, naturally, “stops”. Reels can stop on a symbol or on a blank space between those symbols. On early slot machine games, each symbol would have an equal chance of coming up, but now that computers are running the show, the odds can be convoluted. You might have a cherry on a reel that comes up on average once every 50 spins, while an orange might come up on average once every 5 spins, or any other combination you can think of.

Early slot machines might have only had 10 stops per reel, but now it’s common to have between 30 and 50 stops per reel. The more stops you have on a reel, the easier it is to offer really large jackpots. For example, if you have a game with 10 stops on each reel, with an equal chance of landing on each stop, then your chances of winning any particular combination are 1/10 X 1/10 X 1/10, or 1/1000. If you have a payout larger than 1000 units, you’re losing money on that game.

Modern computers can adjust those odds using a weighting system.

The weighting is what determines how likely a particular stop is to be picked. Suppose you have a slot machine game with 10 symbols, but one of those symbols is special and only comes up once every 100 spins. The odds of getting 3 of that symbol are 1/100 X 1/100 X 1/100, or 1/1,000,000. You could theoretically offer a payout of $1 million on that combination and still break even over the long run. Casinos love that kind of action, and so do players.

Another symbol might be programmed to come up half the time, so your chances of hitting that symbol might be as low as ? X ? X ?, or 1/6. If that pays out at 2 to 1, the casino still makes a significant profit, but the player feels like she’s winning on a pretty regular basis.

The par sheet determines the odds. Every modern slot machine is designed with a par sheet which specifies the weightings for each stop on the reel, including the blanks. That par sheet makes the odds and the house edge for a slot machine game a known quantity—for the casino. Gambling companies keep these par sheets under wraps, though, so players never really get a clear idea of what the odds, the house edge, or the payback percentage is.

One final term you should understand is “payback percentage”. This is a mathematical prediction of how much money the machine will “pay back” over an infinite number of spins. For example, if a machine is programmed to have a 97% payback, over enough spins, the average should come close to winning $3 out of every $100 put into the machine. Casinos distinguish between the theoretical payback percentage and the actual return on the machine, but you can count on one thing. Slots are immensely profitable for the casinos.