How do slot machines work?

Most amateur gamblers believe that if a slot machine hits the jackpot, then it immediately goes ‘cold’. They also believe the opposite is true; if a machine runs cold for hours, then it’s ‘due’ for a big payoff. But if you look inside modern slot machines, you learn the cold hard truth. Every single pull of the lever has equal odds of winning, and those odds are steep.

Since the earliest mechanical slot machines, gaming manufacturers have weighted the machines to tweak the odds. If you look closely at the reels of old machines, you’ll find many more blanks and low-scoring symbols than pots of gold, especially on the third or final reel. This creates the famous ‘near miss’ effect.

Modern slots have replaced the gears, cranks and stoppers with precision step motors and random number generators (RNG). When you pull the crank on a modern slot, a built-in RNG selects three numbers between one and 64. Each number corresponds to one of 22 spots on the three reels. The trick is that half of the numbers between one and 64 correspond to blank spots and only one random number matches the jackpot symbol. The odds of nailing the jackpot are 1/64 x 1/64 x 1/64 or one in 262,144.

The lever is just for show. Three internal step motors spin each reel and stop them precisely at the positions chosen by the RNG. Still feeling lucky?

How do slot machines work?
How do slot machines work?

Return vs payback

There is no such thing as a ‘loose’ or ‘tight’ slot machine. In modern casinos, slot machines are programmed to deliver a precise return percentage, somewhere around 95 per cent. That means 95 per cent of the money that goes into a slot machine is paid back out to the players and the casino keeps the rest.
But here’s where things get tricky. The return percentage is not the same as the payback, which is the actual amount of money you win or lose during each gambling session at a slot machine. If you sat down at a slot machine for eternity and pulled the lever an infinite amount of times, your payback percentage would be exactly 95 per cent. Likewise, in a casino full of gamblers, the collective machines will pay back roughly 95 per cent of the total money gambled during the course of a day.

Unfortunately, you are only one person and you don’t have infinite pulls. So your odds of winning are equally good or bad every pull. You could lose all day and that doesn’t mean the machine is rigged. And it doesn’t mean that the guy who wins the jackpot found the ‘loose’ machine. He just got very, very lucky.

Top 5 Facts: Gambling stats

1) Big jackpot, big odds

The odds of winning the jackpot on a ‘progressive’ slot machine like Megabucks is one in 50 million, although if you are that one you’re likely to become very rich.

2) ‘Easy’ money

68 per cent of people who gamble at Las Vegas play the slot machines most often. And there’s a large target market as nearly 90 per cent of visitors to Las Vegas gamble.

3) The house wins

In the United States, gaming was a $92 billion industry in 2007, double what it was a decade ago. And in the UK, there were 143 casinos as of 31 March 2009.

4) United States of Slots

Even though Nevada is widely considered the gambling state, there are 37 US states with some form of legalised electronic gaming device like slot machines or video poker.

5) Vegas’ most wanted

The Nevada Gaming Commission maintains a list of 35 people who are not allowed in any casino or gambling establishment. Only one of them is a woman.

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