What You Must Know About Slot Machine Bonus Rounds

Slot-Machine-Bonus Star-Chips

If you’ve read any of my blog posts about slot machines before this one, you already have an idea of how a slot machine game works.

A computer program called a random number generator (RNG) cycles through numbers constantly and stops when you hit the spin button on the machine. Since there’s no way to know which number it will land on, the results are random.

Each number on the RNG corresponds to a combination of reel symbols. And each combination of reel symbols has a payout attached to it.

Most of the money you put into a slot machine is returned in the form of a payout, but it’s on an X for Y basis. In the long run, the relatively small percentage of money that doesn’t get returned as a payout adds up into huge losses for the players and huge wins for the casino.

Let’s take an extremely generous slot machine that pays back 97% of the money put into it. How much money does that machine make?

Assume an average bet of $3 per spin, and an average play rate of 600 spins per hour. That means you’re putting $1800 per hour into action.

The machine pays back an average of 97% of that, or $1746, which means you’ve lost $54 that hour of play.

Of course, that’s a statistical average. Some hours, you’ll win some money, and others, you’ll lose more than that amount. But that’s how a slot machine works.

What Happens to a Slot Machine When You Add in Bonus Rounds?

The most important thing to a casino is to get people to spend a lot of time playing on a slot machine. They do this by making sure that the ratio of wins to losses is optimal to keep you motivated. They also want to make sure that the sights and sounds associated with the game are exciting enough to get you playing.

Several years ago, IGT came up with one of the most attractive sights and sounds in slot machine history. They rolled out a slot machine game based on Wheel of Fortune, the TV game show.

The game features a bonus round where you get to spin the wheel, just like you would if you were on the show. This bonus round is so popular that I’ve read stories about players who have won progressive jackpots who were disappointed they didn’t get to spin the wheel.

Other games with popular licensed bonus rounds rolled out soon afterward. Some were based on game shows, but others were based on board games like Monopoly.

The Illusion of a Bonus

On most slot machine games, the bonus round feature doesn’t really give you anything extra. It’s just the illusion of a bonus. Sure, it’s fun watching the wheel spin, but you pay for that bonus round in the form of a reduced payback percentage on the game itself (this is also true of progressive jackpots, but that’s a topic for another post).

Ask yourself this—where does the money paid out in the bonus round come from? It has to come from the base game or the slot machine as a whole couldn’t stay profitable.

I know I used 97% as an example payback percentage earlier, but a more realistic payback percentage might be 92%. That 92% includes payouts from the bonus rounds. This means that during the regular gameplay on the machine, you have less money for payouts.

If 20% of the payouts from the regular game are “diverted” to the bonus rounds, most of the time, you’ll be seeing lower payouts during the regular game.

And since bonus round payouts need to be higher to compensate for this, it means that you’re going to see much smaller and less frequent wins during the base game.

Multiple Payline Games With Bonuses


If you’ve never played a slot machine game, you might think that you just put in the wager amount and hit spin. Then, you’d see if you got three winning symbols in a row across the middle of the machine.

That’s not exactly how modern slot machines work, though.

First of all, most modern slot machines allow you to choose how many coins you want to wager on each spin. You can wager up to 100 coins or more. These limits are determined by the slot machine game’s programming.

On top of that, there are more ways to form a winning combination than just a horizontal line across the middle. On most slot machines, you can see the row of symbols above and below the main payline.

The paylines are like patterns on a bingo card. The problem is, to activate these additional paylines, you must bet money on each of them. And some modern slot machines might have as many as 40 paylines.

This is why penny slots can be so profitable for the casino. If you bet five coins each on 40 paylines on a penny machine, you’re betting $2 per spin.

And the same games that have multiple paylines are usually the ones with the bonus rounds.

The casinos and the slot machine manufacturers are being somewhat disingenuous by making you think you’re getting something for nothing with these bonus rounds.

At the end of the day, though, these little perks just wind up costing you more money.


Slot machines with bonus rounds are almost ubiquitous now, but that doesn’t mean they’re the best slot machine games in the casino to play.

Do you play bonus slots? What’s your experience with them been like? Let me know in the comments.

Posted in: Slots

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