Slot machines are among the most widely played but least understood games of chance in the world today. They’re the most popular games in brick-and-mortar casinos in the United States, where they were invented.

Australia has even more slots per capita than the U.S., and while not quite at that level, slot machines are strong presences in Europe and the major gaming market of Macau.

Online, tens of millions of people play slot games, whether for money in Internet casinos or just for fun in social media apps.

But even to many of the most devoted slot player, how the machines work, the slots terms and the odds of the games remain in unsolved mysteries territory.


The first question I get asked by slot players usually is, “Can you really win on these games?” No. 2 on the popular question list is “Can you tell me how to win?”

That’s natural enough. Everybody wants to know how to win. Here are some answers:

**CAN YOU REALLY WIN ON THESE GAMES? The answer is, “Sometimes.” All the payoffs listed on the game are really available. Anyone who plays very often will have winning sessions, and that may even include some large jackpots and a cause for celebration. But nobody can beat the slots consistently, and over time the casino will collect its percentage.

**CAN YOU TELL ME HOW TO WIN? With rare exceptions, slot machines are pure games of chance. Results are driven by a program called a “random number generator,” and nothing the player can do influences the random numbers being generated. So no, there is no magic formula that will make you win more often than random chance would suggest.


The odd of winning on slot machines are different on different games, on different coin denominations for your wagers, and even sometimes on different machines of the same game and denomination. The odds of individual games are not advertised or posted on the machines.

The best we can do in estimating the odds on slot games are to look at casino-wide averages of games of the same denomination. For an estimate, we can turn to the United States, where casino averages are reported to the public by state gaming commissions.

The percentages differ from casino to casino and jurisdiction to jurisdiction, but a broad overview of paybacks looks like this:

Slot machines usually pay higher percentages with bigger bets. Here are some average returns and house edges, based on public records from state gaming boards in the United States.

Coin DenominationPayback PercentageHouse Edge

1-cent games 84% to 87% 13% to 16%
5-cent games 88% to 89% 11% to 12%
25-cent games 90% to 93% 7% to 10%
1-dollar games 93% to 95% 5% to 7%

**1-cent games: 84 to 87 percent
**5-cent games: 88 to 90 percent
**25-cent games: 90 to 93 percent
**1-dollar games: 93 to 95 percent.

Note that the percent of wagers returned to players as winnings increases as the bet size gets bigger. Those who play more expensive games get a larger portion back, and a better shot to win.

Does that mean you should rush out to make bigger bets? No. You may get a bigger portion of your bets back on a more expensive game, but still lose more money because you have more at risk. Let your bankroll be your guide, and don’t bet money you can’t afford to lose.


As in all casino games, the house has an edge in slot machines because it pays less money than the true odds of the game. It’s easy for a slot player to lose sight of that because we can’t see the numbers that go into slot probabilities the way we can see the numbers on a roulette wheel or a pair of dice. Nonetheless, the odds work in similar fashion.


All casino games are based on math, and slot machines are the most-math intense games in the house. That doesn’t mean you need to be able to do the math, and I don’t want to overburden you with numbers here. But one walkthrough on a simplified slot machine might help you understand how the odds work.

Let’s set up an example that’s as streamlined as slot odds can get, a game of the type used in the early decades after Charles Fey invented the three-reel slot machine in 1895.

A hypothetical three-reel slot game with one 7, two bars, three cherries and four watermelons per reel would have 1,000 possible combinations and return 83.2 percent to players with this pay table.

SymbolsNo. of combinationsCoins per WinnerTotal Coins Paid

7-7-7 1 160 160
Bar-Bar-Bar 8 25 200
Cherry-Cherry-Cherry 27 8 216
Melon-Melon-Melon 64 4 256
Mixed Symbols 900 0 832

In our sample game:

**Each of three reels has 10 symbols. Each reel has one 7 – that’s the top jackpot symbol. Each reel also has two bars, three cherries and four watermelons.

**There are 1,000 possible three-reel combinations – 10 symbols times 10 symbols times 10 symbols.

**Only one combination – or 1 x 1 x 1 – will be three 7s. Eight combinations will be three bars, 27 will be three cherries and 64 will be three watermelons. That’s 100 combinations in which all three symbols are the same, and 900 combinations with mixed symbols.

**If the game paid at true odds, then the payoffs would be set up so that each 1,000 coins wagered would bring 1,000 coins in payoffs. One way to do that would be to have payoffs of 170 coins on three 7s, 30 on three bars, 10 on three cherries and 5 on three watermelons.

**But the casino must have an edge, or it couldn’t pay the bills and offer the game. So instead it pays 160 on three 7s, 25 on three bars, 8 on three cherries and 4 on three watermelons.

**Multiplied by the frequency of wins, those payoffs total 832 coins. By paying less than the true odds of the game, the machine has a payback percentage of 83.2 percent, or a little less than today’s 1-cent games.


Today’s slot machines don’t just have 10 numbers per reel, and most modern video games, both in casinos and online, have five reels instead of three.Game designers and programmers are dealing with hundreds, and even thousands of symbols, stops or random numbers per reels.

Here are some factors that go into modern slot odds:

**When the games are on video, the game programmer can make the reels as long as he needs them to be. If, to get the desired odds, the programmer needs a video reel to have sequences 1,000 symbols long, then he can program a 1,000-symbol reel.

**On games in brick-and-mortar casinos with mechanical reel, the reels can’t be 1,000 symbols long or they couldn’t fit in the machine casing. Instead, programmer’s use what’s called a “virtual reel.” That’s a method for making a smaller reel act as if it had more symbols. A programmer could tell the machine, “Any time the random number generator lands on No. 1, stop on the jackpot symbol. Anytime it generates No. 2, 3, 4, 5, 6 or 7, stop on the first bar,” and so on.

In that way a jackpot symbol that is one of 40 symbols and spaces can be made to come up only once per several hundred times, or even more.

That has a dramatic effect on the odds of the game. When the world record jackpot of more than $39 million was won in Las Vegas in 2003, it was on a Megabucks machine with mechanical reels, random number generator and virtual reel. The odds of winning that jackpot were about 1 in 50 million.

Other machines use much smaller number sets, have smaller top jackpots and pay off more often. The odds still are calculated the same way as our example above, but with larger number sets, many more possibilities and more complicated arithmetic.


Nearly all modern slots include bonus events. Bonus events include many formats, with some of the most popular being:

**A spin of a bonus wheel, marked in segments for prize amounts;

**Pick’em bonuses where you select icons on a video screen to reveal credit awards;

**Free spins of the regular game reels.

During bonus events, you have the chance to accumulate credits without making additional wagers. That has to accounted for in setting odds and paybacks on the regular reel spins. Just how much of a game’s overall return differs from game to game and manufacturer to manufacturer. One gamemaker told me that if the odds on one of his games is set so the machine returns 90% to players, then about 60% comes from reel spins and 30% from bonuses, with the other 10% to the house.


What you see on the reels or video screen are just a user-friendly representation of a game that’s really being played inside the machine’s software, in the random number generator. We can’t see the numbers being generated, so that leads plenty of player questions about the things we can see.

**Do all slot games of the same type have the same odds?

In short, no. Manufacturers make their games available to casino operators with odds set for a number of different payback percentages. Two machines could be sitting side-by-side with identical game names, graphics and pay tables, and have different payback percentages. The same applies online: A game at one online casino doesn’t necessarily have the same odds as an identical-looking game at a different online casino. The random numbers can be applied differently so that winning combinations come up more often on one game than on an identical-looking game.

**Is there any way for a player to tell which is the higher payer?

Again, no. Casinos do not typically post odds and payback percentages on their slot games, and without inside information, players have no way of knowing if one machine is higher-paying than another, or if they have the same programming.

**What can you tell from looking at a game?

While we can’t determine a game’s odds by looking at it, there are several useful pieces of information we can gather from the outside.

*A game with a much bigger jackpot than another usually – though not always – gives less back to players in smaller wins. That makes the game more volatile, meaning you have a better chance to win big, but also a better chance to lose your money fast.

*A game whose main bonus event is free spins usually is more volatile than a game with a pick’em bonus. Free spin bonuses often give you a better chance at piling up big credits, but also bring a risk that you will win nothing in the bonus event.

Those are important factors to players. The games might have similar odds and payback percentages in the long run, but if you’re looking for a game that gives you the best chance to play a while and have a little fun, you want the less volatile game. But if you’re looking for a game that gives you the best chance to win big, you’re looking for more volatility.


There are questions slot players ask over and over again, trying to understand how the games work.

**If I walk away from a game and someone else then wins a big jackpot, would I have won if I had stayed?

Probably not. The slot machine’s random number generator keeps running even when a game isn’t in use. It also moves very fast, generating dozens, even hundreds of random numbers per second. If you’re in a brick and mortar casino and stop to admire a neighbor’s win, your next result will be different than if you’d just kept playing. If you’re playing online and pause a second or two to take a sip of coffee, your next result will be different than if you’d skipped the sip. So if you’re in a casino, stand up, leave the machine and someone else takes your place, the new player’s result is almost certainly different than what you’d have seen if you’d stayed.

**If a big jackpot is paid, does a slot machine have to pay less for a while to make up for it?

No. Jackpots are part of the normal odds of the game. Casinos expect to pay jackpots. They need winners – without winners, no one would play. Over hundreds of thousands of plays, any jackpot just fades into the statistical background of normal odds.

**Is it possible to win twice in a row?

Yes. The last result has no impact on later results. The random number generator continually works with a full set of numbers, so all possibilities are there for every spin. It’s possible to win two jackpots in a row, and even two top jackpots in a row. It doesn’t happen often, but it can happen and has happened. And it’s such possibilities that make playing the slots fun.