Bonus round slots: how they’re made and why casinos need them

Early slot machines were fairly simple mechanical contraptions—you spun the reels and hoped the symbols aligned. Modern slots are a world apart from their predecessors, with various unique mechanics and bonuses. Players love slot games with bonus rounds, developers enjoy creating them, and casinos host them in their thousands.

So, how do bonus round slots work, and why are they so ubiquitous? 

Slots with bonus round mechanics: The basics

Bonus features are unlockable mini-games. They are distinctive from the main game and typically use a different grid and symbol setup. For instance, they may add more wild symbols and multipliers or even expand the reel set. However it functions, a bonus round offers players a higher chance of winning than the main game, and gives them a target to chase.

Players trigger bonus rounds by landing a specific number of scatter or bonus icons. Some rounds also launch at random or via some other triggering mechanic, such as a minimum number of cascades in a cascading reels slot.

For example, Lucky Legion Hold and Win and Lucky Selva Hold and Win both feature a Hold and Win round. Triggered by landing three or more bonus coin symbols, it removes all main game symbols and leaves only bonus coin and jackpot coin icons, a combination of which can produce sizeable payouts.

The inner workings and psychology of bonus round slots

A random number generator (RNG) determines the outcome of bonus games, as it does with main game spins. Developers tie these features to a particular combination of symbols that don’t appear as often as other symbols. As a result, activations are rarer than standard wins, and bonus features may appear once for every 50 or 100+ spins on average.

Bonus features give players a realistic target to chase. The player knows the feature can trigger during any spin, and they know the rewards can be high. However, it’s random, and thus it’s very satisfying when the feature triggers.

Players often get the same satisfaction from a bonus trigger that they’d get from a big win, and if they have any near misses (such as landing two scatters when three are needed), it begins to feel more achievable, so they keep spinning. 

Activating bonus rounds in online slot games

Developers use various mechanics to trigger bonus games. Their goal is to provide a clear and obvious route to the bonus round—one that most players will understand—while still ensuring it’s a somewhat rare event.

Common triggers for slots with bonus rounds include:

• Scatter or bonus symbols: The most common way to trigger features is by revealing a specific number of bonus or scatter symbols, as with Very Lucky and Lucky Crown Plus. Some slot machine games require bonus symbols to line up on an active payline, but with most, those symbols can appear anywhere on the reels. These setups are familiar and make the game more accessible.
• Wild symbols: A wild symbol substitutes for most main game symbols, making it one of the most impactful symbols in any slot. Some games enhance the wild’s impact by tying it to bonus features—it essentially doubles as a scatter, and focuses the player’s attention on the wild.
• Random triggers: A randomly triggered bonus round can launch at any time and on any spin. In recent years, we’ve seen an influx of slots where specific coins/tokens have a chance of triggering a bonus every time they appear, but ultimately, it’s random, and players know they can trigger the bonus even on a non-winning spin.
• Progressive systems: A progressive system keeps the player engaged by requiring them to collect a certain number of symbols. They’re less likely to walk away from a slot if they’re close to a feature trigger, making these systems very effective at increasing retention rates.

Common features in slot games with bonus rounds

Slot developers have many different bonus games at their disposal. They can stick with classics like free spins or explore a visual showcase in the form of an arcade game. 

Improved technologies and higher player demand mean many slots combine features, such as Hold and Win rounds with free spins, jackpots, and pick’em games. The most common bonus features found in bonus round slots include:

Free spin/bonus spin features

Free spins, also known as bonus spins, are the most common features in bonus round slots. They’re also one of the simplest, at least on the surface.

Players are given a number of free spins of the reels, the value of which is set by their triggering stake. Developers mix things up by adding additional features and modifiers to the bonus reels, creating a grid that’s distinctive from the base game and offers higher payout potential.

Seen in slots like Book of Money, Booming Spins 243, and Cash’n Spins 27 Plus, free spin features essentially let players turn one spin into several. While many of these features have fixed totals tied to the triggering scatters (4 or 5 scatters will usually award more spins than 3), others go on indefinitely until the player reveals a specific symbol or reaches the end of a countdown.

Pick’em features

A simple but beloved concept, the pick’em or pick-a-box bonus round presents players with a variety of options and asks them to choose one. They will then receive an instant payout. Most pick’em bonuses are short, but by adding unique visual elements, developers can work these rounds into the overall theme and create a more engaging experience.

Cascading/tumbling reels and the sliders bonus

The cascading reels feature goes by several names, including tumbling reels, avalanche, and rolling reels. It all comes down to how the developer describes the feature, but the concept is the same: winning symbols disappear, new ones replace them, and the process repeats with more payouts.

Cascading reels are typically available in the main game + bonus round (usually a free spins bonus). However, with the rare sliders bonus, developers stick to standard main game formats and only add cascading reels to the bonus feature. It adds more depth to the bonus round and creates more of a spectacle.

Mini-games and gamble features

Many bonus games function like mini arcade games. Players advance through multiple levels, collecting modifiers and payouts as they go. The mechanics vary, and can include everything from cheering on a horse in a race or scoring penalties in a football-themed slot to advancing along a trail. 

Many developers also add gamble mini-games to their slots. These optional games become available after every payout. If launched, the player can choose to risk their recent spin winnings on a double-or-nothing game. 

More often than not, gamble mini-games transport players to a card game where they choose whether the next card will be red or black. They can also risk their winnings on a 4x return by guessing the suit of the next card.

Interactive bonus rounds

Slots use random number generators (RNG) that effectively determine the outcome as soon as the player hits the play button. They are also games of chance that don’t require skill or prior game knowledge. As a result, it’s difficult to make bonus rounds fully interactive, but developers have found ways to insert partial interactivity.

Using the above example of arcade games, players may be asked which direction they want to take on a trail bonus or where they want to direct the ball in a football bonus. Their decisions don’t always impact the outcome, but interactivity engages the player and immerses them in the experience.

How bonus rounds benefit casino operators

Player retention is everything in the online casino sector, and even the slightest increases in retention rates can significantly boost total revenue. Slots with bonus rounds could play a major part in every casino’s efforts to keep players engaged.

Studies show that players are more drawn to bonus round slots. One study in particular compared slots with bonuses to those without, and found that participants were much more likely to engage with the games that had bonus rounds.

It’s the anticipation of something big—free spins, wilds, multipliers, mini-games—coupled with the potential for major payouts. It also feeds into the psychological need to have that one more spin and take one more chance. 

For many players, a bonus round is the ultimate goal of playing that slot, and they won’t walk away until they’ve triggered it. What’s more, if they eventually trigger the bonus feature and like what they see, they’ll want to keep spinning to repeat that process.

You don’t always need big 3D graphics and complex payline mechanics to make a slot game appealing. We’ve proved that with retro-themed slots like Mystical Luck Hold and Win and Classic Chilli Hold and Win. But for many players, bonus rounds are essential, and considering the impact they have on engagement, they are just as essential for casino operators.

Incorporating bonus rounds into the development process

During the slot development process, the developer must first consider whether they want to implement bonus rounds, as well as which bonus rounds to use. From there, they need to think about:

• How it influences the mechanics: Developers can’t simply attach a bonus round to an existing slot and hope for the best. It could drastically alter the volatility and RTP, so the game must undergo lengthy testing in its final state to calculate accurate metrics.
• How often it triggers: A bonus round that triggers too often loses its power. Players want to unlock these features because they’re infrequent and rewarding, and that stops being the case if they trigger every few spins. At the same time, players may get frustrated if the features trigger far too infrequently. Balance is key.
• How much it pays: Players expect to get something from a bonus feature, and will be disappointed if it rewards less than the average main game spin. However, it can’t be so generous that it tanks the casino’s profits. Again, balance is important—it should be enticing, with occasional big payouts, but not overly generous.
• How it ties into the theme: A good slot supplier will always tie the bonus to the theme. They’ll consider how it looks and sounds, and whether their choice of feature is a good match for the overall aesthetic.

Bonus round slots in the 1spin4win roster

Most 1spin4win slot games include bonuses. We tend to lean toward classic slots that utilize retro styles, but at the same time, we understand the importance of bonus rounds and unique features.

Hold and Win is a great example. It’s a respin mechanic that offers something different from traditional free spins, and it works well with fixed jackpot payouts. Players love it, and so do we, which is why we use it in so many of our top titles, including Lucky Arena Hold and Win, Lucky 1spin4win Hold and Win, and Gold Oceanica Hold and Win.

We still use free spins, as seen in Gems and Cash Win Spins, but we like to mix things up and use engaging, unique bonuses where possible. Don Catleone Win Spins, with its titular Win Spins feature, is a prime example.

Final thoughts: Bonus rounds and the power of engagement

Slot games with bonus rounds typically perform much better than games without. There are still players who prefer simple layouts and single-screen gameplay, but they are in the minority. 

Modern players want originality, but at the same time, they expect to see classic features and bonus rounds in their online slots. Slot developers cater to these players by adding bonuses like free spins and Hold and Win, and by implementing fun twists and modifiers whenever they can.

FAQs

‍What are bonus features?

They are unlockable mini-games or free spin/respin features in online slot machines.

How do slot bonus rounds work?

It depends on the specific feature, but most trigger with scatter/bonus symbol combinations and offer a chance of big payouts.

What’s the most common type of bonus round in a slot game?

Free spin features are the most common, as they’re very popular with players and don’t deviate too much from the base gameplay.

Why should operators care about slot game bonus rounds?

Bonus rounds drive engagement and improve player retention. They keep players spinning in the hope of triggering a feature. They also expand on the gameplay loop to add more depth and prevent players from growing tired of the core mechanics.