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Gambling problem?
  1. Call the 800-522-4700 hotline or get online help
  2. See these horror stories.
  3. Know that Parkinson's drugs encourage gambling.
Play these
free slots now

Gambling problem?
  1. Call the 800-522-4700 hotline or get online help
  2. See these horror stories.
  3. Know that Parkinson's drugs encourage gambling.

How slot machines are random

by Michael Bluejay | Last update: August 2018

Note: This article covers traditional slot machines.
The new skill-based slots are covered on a separate page.

Play this slot machine with play money or real money at Bovada

No popups, no download, no registration, no B.S., just the game. One click and you're in.

Why you can trust this info

Myths and misinformation about slots could fill a book!  So here's why you can trust this article over what you might see elsewhere:

  1. I've done the actual mathematical design of actual slot machines myself, professionally, for-hire.  But if you don't believe that...
  2. I programmed my slot machine simulator the exact same way that real slots work, with every spin being completely random.  You can run it for thousands of spins, and see that it returns the expected payback, without any shenanigans like the slot continually getting looser and tighter over time.  But if you don't believe that...
  3. I use the very best sources, such as actual slot machine par sheets from the game manufacturers, and the actual Nevada Gaming Commission regulations on slots.  The par sheets describe the actual probabilities of the games, and the laws dictate that spin results must be random.  Those who spout B.S. (like that machines constantly get looser and tighter) cite no sources.
  4. I was an assistant to the legendary Wizard of Odds for ten years; he's done the programming for countless slots for online casinos (which work exactly like their real-life counterparts), and I helped him with his early slot research, even before he published his infamous survey in of how loose and tight various Vegas casinos were.
  5. I've written professionally about the industry, outside of this website.  Casino Player magazine trusted me enough to run one of my articles as a cover story.

I also put my money where my mouth is.  To show that there's no such thing as a winning slot system, for years I've offered $10,000 hard cash to anyone who could demonstrate a winning system.  No system-seller has ever dared take me up on it, because they know their systems don't work.  I also used to offer a separate challenge to those who claim that higher-paying slots are located in certain areas of the casino, but I retired that one after many years because it was hard to keep up with all ways people kept trying to find loopholes to exploit the test, and nobody ever took me up on it anyway.

With that out of the way, let's look at the randomness in slot machines.

Slot machines are based on randomness

The basis of slots, and in fact every classic game in the casino, is that the outcome is totally random.  Random means that the results occur without any bias or influence.  This doesn't mean that you're just as likely to win as lose.  For example, let's say our game is rolling a single die, and you win if it lands on 1 or 2, and lose if it lands on 3, 4, 5, or 6.  Each number is equally likely to be picked, but losing numbers are more likely than winning ones.

On a slot machine, the computer program picks a random symbol on the first reel, then the next, and so on.  You're not likely to get the jackpot, because there are so few jackpot symbols on the reels, so they're less likely to be picked.

The probability of lining up the winning combinations, combined with the payout for those combos, is what determines the payback of the machine.  (The payback is the percentage of money returned to the player on average, and is ninety-something percent on most slots.  See more on paybacks.)  It's this randomness that ensures the long-term payback of the slot.

This randomness means that nothing affects the result:  machines continually don't get looser and tighter to meet a specified payback, jackpots don't get more likely just because they haven't hit for a while, the presence or absence of a player's card doesn't change the results, etc.  Every spin is completely random.

Some people write in asking, "But, but, does [thing X] affect the outcome?  Because you didn't mention [thing X] specifically."  The answer is still the same.  I can't predict all the ways people will come up with that they think might change the spin results, so whatever you want to ask about, then yes, it's included, even if I didn't mention it specifically.  Every spin has identical chances as the previous spin, period.

If you're satisfied with this answer, then you can stop reading here, and graduate to my article on how slot machines work.  If you're still skeptical that slots are completely random, then read on.

The machines don't get looser and tighter to meet the payback percentage

Probably the biggest myth about slots is that they continually get looser and tighter to meet the specified payback.  It seems that way because people who haven't run through the math think that a specified payback and the randomness principle are mutually exclusive, that you can't have a certain payback if the machine is random.  In fact, it's the opposite:  the randomness is what creates the payback.

Here an example:  We'll use a bag of marbles, 95 black and 5 white.  You bet a dollar every time you pick one out of the bag blindly.  When you pick a marble, if it's black you get your dollar back, and if it's white you don't.  (Damn honkies.)  It should be pretty easy to see that this is a 95% payback game.

We could turn this game into a machine version by telling the machine to simply pick a number between 1 and 100, and pay you back if the number was between 1-95.  I hope it's clear that the randomness is what ensures the 95% payback.  The machine doesn't have to get looser and tighter, as long as the picks are random, you'll get back 95%.

Here's another example:  Let's say you bet $1 on the flip of a coin, and you get 90¢ when you get heads (and you get your original dollar back), but when you get tails, you lose your whole dollar.  This is also a 95% game.  The machine version would simply pick a 1 or a 2, and pay you the $1.90 if it picked the 1.  For two plays, resulting in one heads and one tails, you paid $2, and got $1.90 back.  ($1.90 ÷ $2.00 = 95%.)  Just as with the marbles, the randomness ensures that the long-term payback is 95%.  The machine doesn't have to get looser and tighter to meet it.  A random result means a 95% long-term payback.

While these examples are simple games, slots work the exact same way.  The casino just dresses up the game with lots of reels and symbols and a paytable to disguise the fact that the machines are a bad bet.  After all, the example games above seem like obvious sure-losers, and you weren't interested in playing them, right?  Who would?  So the casino makes the games complex so they're more interesting and so the math behind them isn't as blatantly easy to see.

Why some people have a hard time accepting slot randomness.

The main reason people cling to the idea that slots get looser and tighter is that they've never seen the explanation.  Without understanding the math, it can sure seem like a slot that's supposed to be, say, 95%, can't achieve that if it's completely random.  But I hope the explanation above has been enough for such readers.  It's not enough for all of them.  (One of them wrote me, "Have fun deceiving people.")

Another reason that some people deny randomness is that it's human nature to look for cause and effect.  That's what we do, and we do it because it's natural for us to do so.  We also do it because we want to feel that we're not completely helpless against a random result.  Feeling that nothing changes the outcome, and especially that we're powerless to affect that outcome, is pretty damn disturbing.  We all want free will!  However, this discomfort doesn't make the truth any less true.

And finally, let's face it, some people are just really easy to fool.  That's why a frightening number of people thought that Hillary Clinton was running a secret pedophile ring in the basement of a pizza shop, that Obama is Muslim, etc.

Randomness is the basis of every classic casino game, not just slots.

It shouldn't be hard to believe that slots are random, because all the other casino games are.  If randomness works for craps and blackjack, why wouldn't it work for slots?

Classic casino games work on this basic principle:

  1. In every round there's a random result (from dice being thrown, cards being dealt, or reels being spun).
  2. When you win, the payout is less than the odds of winning.

There's no mystery about slots, just like there's no mystery about craps.  Why would there be?

In both slots and table games, the casino wins because it has a built-in mathematical edge on the games.  The casino doesn't have to screw with the dice to beat players at craps, they don't have to screw with the cards to beat players at blackjack, and they don't have to screw with the machines to beat the players at slots.  The payline symbols are chosen at random, and it's the math that ensures that you're a long-term loser.

Randomness is dictated by law.

Every jurisdiction mandates that the outcome of non-skill games be completely random.  That goes for both table games and slots.  Slot makers therefore make the machines completely random, because they couldn't sell them otherwise.  (Many jurisdictions actually test the games to make sure they're properly random before the games can be put on the floor.)  So, even if the casinos wanted the machines to operate other than randomly, they don't have a choice.  First of all, somebody else already made the game random, and even if it were possible for the casino to change the programming, it would be highly illegal to do so.  For example, this is from Nevada Gaming Regulation 14 (PDF):

"[A gaming device] must use a random selection process to determine the game outcome of each play of a game...Each possible permutation or combination of game elements which produce winning or losing game outcomes must be available for random selection at the initiation of each play....The selection process must not produce detectable patterns of game elements or detectable dependency upon any previous game outcome, the amount wagered, or upon the style or method of play."

There you have it.  Slots are random, period.

Randomness is shown on PAR sheets.

When a manufacturer makes a slot, the first thing they do is create a PAR sheet.  It's a list of the symbols for each reel, and the paytable for the winning combinations.  From that, anyone with halfway-decent math skills should be able to calculate the payback for a simple slot without bonus rounds.  (Bonus round math is a bit trickier, but still just as random.)  It's thus perfectly clear from manufacturer's PAR sheets that the randomness of landing the available symbols, married to the paytable, dictates the payback.  I have the most comprehensive list of par sheets available anywhere.

Slot machine simulator returns the proper payback by operating randomly.

I programmed a virtual replica of a Blazing 7s slot machine using the original PAR sheet from the manufacturer.  There are no graphics, you just tell it how many times you want it to spin, it does so (invisibly), and then tells you the result.

I programmed it to pick symbol stops completely randomly.  I did not tell it to take previous results into account, and to tighten up if it had been paying out "too much" recently.  I know how the slot works, because I'm the one who coded it, from scratch.  Here's the actual code for picking the result for each reel:

           rnd = Math.floor(Math.random(seed)*72)+1;

Anyone who understands computer programming can verify my code by going to the simulator page and choosing View Source in their browser.

Anyway, this slot, running completely randomly, and without ever getting looser or tighter, properly returns the expected payback in the long run.  The randomness ensures the results.

If you're now convinced that slot spins are random, then congratulations!  You've graduated and can proceed to my article on how slot machines work.  If you still think that slots get looser and tighter in order to meet the specified payback, then I'm sorry.  I tried.

Play slots online

I suggest you play something other than slots because the slot odds are so bad.  You could also play online with fake money, because then it doesn't matter if you lose.  A good casino for free-play is Bovada, since it requires no download and no registration—one click and you're in.  You can play with real money too, though I hope you won't (or at least won't bet more than you can comfortably afford to lose).

Play these
free slots now

Gambling problem?
  1. Call the 800-522-4700 hotline or get online help
  2. See these horror stories.
  3. Know that Parkinson's drugs encourage gambling.

All my slot machine articles

  • Slot machine basics.  How much it costs to play, how much you can win, expected loss, why they're a bad bet, why they're popular, how you can limit your losses, speed of play
  • How to play slot machines
  • Slot returns.  How much they pay back.
  • The Randomness Principle.  Slots don't continually get looser and tighter as they're played.  They don't have to.
  • How they work. Explains the randomness principle, and runs through the math to show how a game returns a particular payback percentage.  There's a companion page on Par sheets.
  • Slot Machine Myths
  • Slot Machine B.S.  Wrong info that's published elsewhere.
  • Strategies. Tips for increasing your chances of winning, and saving money.
  • Slot Jackpots.  Odds of hitting the jackpot, progressive jackpots, and other jackpot topics.
  • Skill-Based Slots.  The scoop on the new games in which your results aren't entirely determined by chance.
  • Slot Machine malfunctions. How and why slot machines screw up, causing players to think they've won the jackpot when they really haven't.
  • Slot Machine Simulator.  I programmed an exact replica of the Blazing 7s slot (odds-wise).  Click it to play thousands of spins in one second and see how you do.
  • List of good Bovada slots.  I spent a full day surveying Bovada's voluminous offerings and extracted only the few with nice, modern graphics and mobile-compatibility.