• The good news: slot machines can be beat outright.
  • The bad news: most of what appears on the Internet and what's written in most books on the topic is nonsense.
  • The truth: learning practical methods to beat slots takes study and legwork. But, once you know some basics, you will find opportunities everywhere when you play slots.

Over the years I have helped numerous companies design their slot machines. This includes creating scores of PAR sheets (a PAR sheet is the slot's mathematical analysis used for jurisdictional and regulatory approval). These spread sheets are the facts behind the slots, the whole truth. There is nothing in these PAR sheets that is different from what the user encounters on the floor. A skilled slot mathematician knows when he may be creating advantage play opportunities. It's his duty to report these issues up the line.

I'll start with an example that I know very well because I designed the slot.

The basic setup for the slot was that it was a "bingo game." What this meant was that the video display showed bingo cards that were dealt "at random" and then balls were dropped "at random." The matching numbers then got blacked out on the card. If the blacked out numbers formed various winning patterns then the game paid out various amounts. I designed about a dozen of these, with a range of thematic designs and mini-games (a game within a game). These were distributed nationally in the U.S. into a number of "bingo only" jurisdictions. Typically, these machines could be set to returns of 87%, 92% or 95%.

So, how could you beat these "perfectly designed" machines? 

In one jurisdiction the ball drop did not happen fresh each time the slot was played. In fact, there was only one ball drop per day and that drop occurred at a remote location. After the ball drop, the data was sent electronically and that specific ball drop was used on every machine in the jurisdiction for the next 24 hours. This procedure would be completely safe if the bingo cards were randomly created. Fixed balls and random bingo cards still equals a random outcome. 

However, the bingo cards were not random. In fact, the company had a set of 250,000 predetermined bingo cards, the "perm set." Each time a game was played the machine would go to a randomly chosen card in the perm set and play out the game on that card. 

Therefore, if you knew the ball drop and the perm set you could compute the RTP for that day. A fixed ball drop and a fixed perm set gave a fixed RTP that would be different than the theoretical RTP based on random events. When I did the calculations, I discovered that the RTP varied day-to-day from about 50% to over 150%. If a user knew the perm set then he could wake up first thing each morning, compute the RTP over that day's ball drop, then get an edge of up to 50% over the house. On the days when the ball drop gave the house the edge, he simply did not play.

I brought this problem to the attention of the person who hired me. We agreed that it would take extraordinary effort to beat the game in this fashion. He stated that he didn't want to derail the game by passing this information up the ladder in his company. So there you go - a potential 50% edge over the house. Given the various non-disclosure agreements I signed, there is only one reason I can tell you about this situation in this article: the company went bankrupt.

I have a very good friend who is one of the top slot mathematicians in the world. This person mentored me, teaching me many tricks to handle a variety of difficult calculations. Over the years she has sent me numerous PAR sheets to ask for a second opinion on possible advantage play strategies. Most recently she bcc'd me on an email she sent to one of her clients in which she refused to complete the requested work. She determined that the advantage play issues with the design were insurmountable. The slot company found another mathematician and the machine is now live in casinos. 

The most famous beatable game my friend did the math for was "S&H Green Stamps."

Slot machine screen with the title

In the lower right you see the text, "Collect More to Win More." As the player played, every time a "Green Stamp" symbol appeared, this meter would go up. At a certain point the player could cash in his stamps. This is an example of a so-called accumulator slot. The player collects something of value throughout his play, and when he has collected enough then he gets some sort of bonus.

So how does this game get beat? The advantage player vultures them. That is, he walks around the casino looking for machines that have unused accumulated stamps. Ordinary players will often abandon primed machines. Maybe they are done for the day, or just feel like playing on a different machine. Regardless, they leave machines in a state where the player has the edge. 

Dozens of different accumulator slot designs have been created. These slots have made it to casino floors internationally.

More recently, so-called must-hit-by progressives (also known as mystery progressives) have been high up on the advantage player's list. These are progressive jackpot slots where the jackpot must be paid out before it rises to a certain dollar amount. Because these jackpots increment by a fixed amount on each spin, as the jackpot get larger there is a higher chance it will hit. At a certain point the likelihood of hitting the progressive jackpot is high enough so that the edge flips to the player side.

Mustang Money Slot Machine

There is a well-known formula (see this book) that can be used to tell the exact dollar value of a jackpot on a slot at which the edge flips to being in the player's favor. Like accumulator slots, the advantage player is wandering through the casino looking for must-hit-by progressives that have a player edge.

Between accumulator slots and must-hit-by progressives, the able advantage player has plenty to do. He wanders the casino floor with a list of slots in hand, looking for an abandoned accumulator or a primed must-hit-by. He may know how to beat 50 or more different slots. More likely he is part of a team, ready to pounce on a group of linked must-hit-by progressive slots while vulturing accumulators and Ultimate-X video pokers. 

From the casino side, the player is not beating the house by beating these slots. Progressives and accumulators are going to be paid out eventually. The advantage player is simply winning money left for the taking by less knowledgeable slot players. In this sense, it is a more innocuous brand of advantage play than methods that directly win the house's money. 

Over the past year I learned that there are smart phone apps that can be used to hack the RNGs on certain slot machines. These allow the player to know where in the RNG cycle the game is, and therefore to know when various jackpots are going to hit. This method requires a particularly stupid implementation of the RNG by the manufacturer. For example, seeding the RNG with a known value or using a short-cycle or predictable RNG. I know this situation actually happens because I have helped debug several slot machines that were having exactly these RNG issues.

In the words of an anonymous slot professional I know,

To the few of us "Machine AP's" that actually exist in the world, almost all of us know about the 5 or 6 games from a very specific manufacturer, on a very specific cabinet. The running gag between us being the belief that someone high up in that company HAD to be an AP for so many of their themes to be vulnerable.

That said, I want to emphasize that hacking an RNG is almost certainly illegal in your jurisdiction. I know two websites (both located on Russian servers) where you can purchase RNG prediction apps for these games. You can also find information about it on YouTube.  I'll leave it to you and your good friend Google to find them. Anyway, don't do this.

As manufactures release new ideas and math models onto the floor, the selection of beatable slots only increases. With the next generation of "skill-based" slots entering the market, a whole new genre of beatable games may be on the horizon. What's certain is that if it's possible to beat any of these new games, then professionals will be there on day one to cash in.

Received his Ph.D. in Mathematics from the University of Arizona in 1983. Eliot has been a Professor of both Mathematics and Computer Science. Eliot retired from academia in 2009. Eliot Jacobson