The Slot Machine: What Every Player Needs to Know

Many people enjoy slot machines.

Before play, most set a money limit – that is, the amount they intend to spend.

Difficulties arise when people exceed their limits.
To keep your risk low, it’s important to know how slot machines work.

The following illustration describes how a slot machine works with a simple bag of marbles.
To begin, we’ll have 19 losing white marbles and a single red win.

In order to make the outcome random, the bag is given a good shake. Now, there is no way to predict where the red marble is.

On each play of the slot machine, your bet allows you to reach into the bag and take out one marble. Since there are 20 in all, your chance of winning is 1 in 20. You take out a marble and it’s white – you’ve lost this time.

Now, stop and ask yourself what the chance of winning on your next bet is. There are 19 marbles left in the bag – 18 white and one red. It would be natural to conclude your chances have improved. That is, you might think your chance of winning is now 1 in 19.
However, this is not the case.

Before your next play, you must first place the losing marble back in the bag, bringing the chance of winning back down to the same as your first draw – 1 in 20.

No matter how many times you draw, your chance of winning remains exactly the same – it never gets any better.

This is the “reload” feature. Your slot machine reloads after every play on every slot machine. The losing marble always gets put back in the bag.

But, you say, at 1 in 20, you’ll win sooner or later, so it’s not that bad a deal.

However, on real slot machines, the chance of winning a jackpot is much lower. It varies slightly from one machine to the next, but your chance of winning is about 1 in a million.

To better understand your true chances, imagine a bag holding one million marbles and, buried in the million marbles is the single red jackpot.

For each and every play, your chance of winning the jackpot always stays at one about in a million. Past wins or losses have no bearing on the outcome of the next spin. Thus, persistence at a particular slot machine will not pay off.

Given what you’ve learned, here are two habits for playing responsibly.

  1. Set your limit: before heading to the slots, decide how much money you can afford and are prepared to lose.
  2. Remember your odds: When tempted to go over your limit, remember the odds are stacked against you. The likelihood is, you will lose.

This resource is produced under a partnership between the Carleton University Gambling Lab and the University of Waterloo Gambling Lab, and funded by the Ontario Problem Gambling Research Centre (OPGRC) and the Interprovincial Lottery Corporation (ILC).

For information on how to obtain Royalty Free Licensing rights to use this video please contact OPGRC at