The Psychology of Free Spins in Slot Machines

Free spins are one of the most attractive features of modern slot machines. They promise “extra play for free,” exciting animations, and boosted win chances. But are they really just a harmless bonus — or do they play a deeper role in gambling behavior?

A doctoral thesis from Victoria University of Wellington investigated this very question, revealing fascinating insights into how free spins influence player preferences, behavior, and risk of problem gambling.

This article is based on a doctoral thesis submitted to Victoria University of Wellington in 2017, which explored the role of free spins in slot-machine gambling. The research investigated how free spins influence player preference, betting behavior, and persistence, using carefully designed laboratory experiments. By translating these academic findings into accessible insights, I aim to show what free spins really mean for players and regulators — beyond the flashing lights and exciting animations.

Key takeaways:

• Free spins enhance player preference, not persistence – they attract players but don’t significantly affect their tendency to continue playing despite losses.
• Simple free spins are less effective than complex ones – basic spins are less preferred compared to those with added effects like animations and music.
• Free spins encourage riskier betting – players tend to bet more, especially on the triggering spin, increasing risk without fully realizing it.
• Perceived excitement outweighs rational decisions – players often prefer machines with free spins, even if other machines offer higher RTP, due to excitement.
• Free spins increase time-on-machine and player engagement – they help casinos boost playtime and engagement through anticipation and perceived value.

Why Free Spins Matter

Free spins are one of the most eye-catching features in modern slot machines, and research shows they play a central role in both player enjoyment and the psychology of gambling. They are not just about giving players “something extra.” Instead, they combine design, reward mechanisms, and psychological triggers that make slots more compelling.

A Core Part of Slot Machine Design

You can’t find a modern slot machine that doesn’t have any bonus or free rounds in its design. Studies show that free spins are no longer a minor bonus — they are built into the mathematics of the machine:

• In real machines analyzed by researchers, over 20% of the total return to player (RTP) came from bonus rounds.
• Players typically spend around 11% of their game time in free-spin modes, meaning these features are not rare events, but a regular part of play.

This makes free spins a fundamental structural element, not a side attraction.

Modern bonus rounds are design with extra sound and visual effects and can last longer than basic spinning.

Player Perceptions

Let’s discuss what a player feels when expecting a free spins round. Gamblers themselves consistently highlight free spins as the most exciting part of slots:

• In interviews and surveys, both casual and problem gamblers ranked bonus features and free spins as one of the main reasons for choosing a machine.
• Many described free spins as the most addictive part of modern slot play, more critical than jackpots or visual themes.
• Focus groups conducted for the New Zealand Ministry of Health reported that “free spins were discussed as the most attractive and important feature of electronic gambling machines” and were strongly associated with increased gambling sessions.

The Illusion of “Free”

The UKGC has even banned calling them “free spins”; instead, they are referred to as bonus spins, additional spins, etc. in the ads. While free spins feel like an extra reward, the thesis highlights that they are an illusion of freeness:

• No balance is deducted during free spins, but the overall payout rate outside the bonus is reduced to compensate.
• In effect, players receive more exciting bursts of rewards in the bonus round, but the game is mathematically adjusted to maintain a consistent long-term RTP.
• This design enhances short-term excitement while disguising the long-term cost.

Psychological Triggers

Free spins also exploit well-known psychological mechanisms:

• Goal orientation: Players view “unlocking free spins” as a target, providing them with a sense of progress and achievement.
• Flow and immersion: The flashing animations, music, and interactive elements of bonus rounds help players “tune in” and block out external thoughts, a state often described as being in “the zone.”
• Conditioned reinforcement: Because bonus rounds usually pay out more frequently or at higher multipliers, the signals that announce free spins (symbols, sounds, animations) themselves become mini-rewards, conditioning players to anticipate them eagerly.

I remember myself hunting those special symbols for a bonus round its really a thing.

Why They Keep Players Engaged

Ultimately, free spins matter because they combine:

• The anticipation of triggering a bonus,
• The heightened excitement of music and visuals during the feature,
• The perceived value of getting extra spins “for free,” and
• The burst of higher wins that are only available during the bonus.

This powerful mix of mathematics, design, and psychology makes free spins one of the most effective tools casinos use to increase time-on-machine and player engagement, even if they don’t necessarily make gamblers more persistent in the face of losses.

Player Preference: What the Research Shows

The thesis conducted multiple laboratory experiments where participants played on two otherwise identical slot-machine simulations: one with a free-spins feature and one without. This allowed researchers to isolate the effect of free spins and measure how much players actually preferred them.

Simple vs. Complex Free Spins

The research revealed an important distinction:

• Simple free spins (a basic feature with no added effects — just a few spins without deducting balance) were not strongly preferred. Participants treated them as an extra spin, but not as a major attraction.
• Complex free spins, however, were a different story. When the feature included animations, music, on-screen messages, and an increased win rate during the bonus, players showed a clear preference for the free-spins machine.

This shows that it’s not the “freeness” alone that matters — it’s the multimedia package and the sense of excitement that drives attraction.

Im personnaly look for and extended bonus rounds with some progression bard, etc. To feel like Im playing an addiotional version of the game.

How Preference Was Measured

Instead of just asking players which machine they liked more, the thesis measured preference by recording how many spins participants allocated to each machine after being exposed to both. This created a graded measure of preference:

• Some players gave 100% of their spins to the free-spins machine (an extreme preference).
• Others split spins more evenly, showing only a mild attraction.

This method revealed degrees of preference, not just yes/no choices, and confirmed that the added features (music, visuals, enhanced wins) were crucial in making free spins appealing.

I personally would spend all free spins (as a deposit bonus) at my favourite slot rather than playing multiple different slots.

Effect on Betting Behavior

The experiments also looked at bet amounts, and the results were telling:

• Players tended to bet more on machines with free spins.
• In particular, the bet placed on the triggering spin (the spin that activates the free-spin bonus) carried over into all the bonus spins. This created an incentive for players to increase their wagers, as higher bets resulted in higher payouts during the bonus.
• This mechanism subtly encourages riskier play without players always being aware of it.

Real Money vs. Hypothetical Money

A later experiment tested whether player preferences changed when they gambled with:

1. Hypothetical credits (play money), or
2. Credits exchangeable for real rewards.

The outcome?

• Players showed a similar preference for free spins in both conditions.
• However, when using hypothetical money, they tended to place larger bets and gamble for longer periods.
• This suggests that free spins are inherently attractive, but the willingness to gamble more heavily may be linked to the perceived “safety” of not risking real funds.

RTP and Player Sensitivity

Another interesting finding was that players were generally insensitive to RTP (return to player) differences when choosing between machines. Even when one machine mathematically offered better long-term returns, participants often continued to prefer the free-spins machine if it had the complex bonus features.

This suggests that perceived excitement outweighs rational expected value — players tend to go where the fun is, not necessarily where the odds are best.

Key Insights from the Experiments

• Free spins are not equal: basic versions have little effect, but enhanced versions drive strong preference.
• Multimedia cues (animations, sounds, increased wins) are the fundamental drivers of attraction.
• Betting patterns change: players wager more on machines with free spins, especially on triggering spins.
• Free spins are appealing across contexts, whether playing for real or hypothetical money.
• RTP has little effect compared to the psychological impact of free spins.

Do Free Spins Cause Persistent Gambling?

One of the most important questions about free spins is whether they encourage persistence in gambling — continuing to play despite losses, which is a hallmark of problem gambling. To test this, the thesis developed a new persistence-measuring task based on principles from Behavioral Momentum Theory.

The Persistence Task

Participants played two slot-machine simulations in a multiple schedule design:

• One machine included the complex free-spins feature (with animations, music, and increased win rates).
• The other was a control machine with no bonus.

The experiment had two phases:

1. Baseline phase: Players gambled normally, alternating between the two machines.
2. Disruption phase: Distractor video clips were embedded into the screen to interrupt play.

By comparing the rate of gambling during the disruption phase to the baseline, researchers measured how persistent players were, with the idea that more resistant play (less slowdown during distraction) indicated stronger persistence.

Findings: Free Spins and Persistence

Surprisingly, the results showed that free spins did not make players more persistent:

• Players did not continue gambling at higher rates on the free-spin machine once disruptions were introduced.
• Even though free spins increased preference and enjoyment, they did not significantly increase resistance to stopping when play was interrupted.
• In other words, free spins hook attention but don’t necessarily deepen compulsive persistence on their own.

Testing Win Frequency

Another line of research investigated whether different win frequencies (i.e., the frequency of small wins) affected persistence. The outcome was similar:

• Players did not gamble more persistently on machines with higher win frequencies.
• Persistence seemed unaffected by these subtle variations in reinforcement schedules.

This suggests that single slot-machine features in isolation do not easily manipulate persistence — it may require a combination of design elements, context, and personal risk factors to drive compulsive persistence.

Implications for Gambling Theory

The results also carry implications for Behavioral Momentum Theory, which suggests that persistence should vary depending on reinforcement history. The experiments showed that comparing disruption phases to baseline may not be sensitive enough to detect small differences caused by free spins or win frequency.

This means the psychological “weight” of free spins lies more in attraction and preference than in long-term persistence. They make players choose a machine, bet more, and stay engaged, but they don’t necessarily increase the stubbornness to keep playing when obstacles arise.

Key Insights from Persistence Studies

• Free spins increase enjoyment and preference, but not persistence in the face of distraction.
• Changing win frequencies also did not boost persistence.
• Persistence seems to be influenced by multiple factors (structural features, individual vulnerability, context), not free spins alone.
• From a regulatory perspective, removing free spins might reduce player enjoyment but would not significantly reduce problem gambling persistence.
• The persistence task developed is a valuable tool for future research on how other slot features (jackpots, near wins, losses disguised as wins) might affect gambling resistance.

I remember one of my first slot machine experience was a 3 reel NetEnt slot with tier jackpots. And it often show a near-win spin when I needed just one diamond symbol to hit the jackpot. And its a rea thing that effects your perseption of the game.

Conclusion: Implications for Players and Regulators

The thesis results offer important lessons for both casino players and regulators. While free spins clearly increase enjoyment and machine preference, their effect on persistence is more limited. This balance has different consequences depending on perspective.

Implications for Players

1. Free spins are not truly free. The machine compensates for these bonus rounds by lowering payouts during standard play, meaning the overall return-to-player (RTP) remains constant.
2. The thrill of the bonus creates an impression of extra value, but mathematically, players are not gaining an advantage.
3. The research found that players often bet more on machines with free spins, particularly on the triggering spin, since this bet amount carries through the entire bonus round.
4. This design encourages players to engage in riskier betting behavior, even if they are not consciously aware of it. Free spins make slots more entertaining and immersive, with music, visuals, and boosted wins.
5. However, they did not make players more persistent under disruption in lab studies. This suggests free spins attract attention and extend sessions, but are not the sole driver of gambling addiction.

Free spins are best understood as a psychological hook: they increase excitement, encourage larger bets, and make slots more fun, but they don’t change the long-term odds.

Implications for Regulators

1. Removing or banning free spins could reduce enjoyment for recreational players, but may not significantly reduce problem gambling persistence.
   This creates a policy dilemma: free spins are highly appealing, but they don’t directly fuel compulsive play in isolation.
2. Regulators could require casinos to disclose how RTP is redistributed during free spins clearly.
   • What percentage of RTP comes from bonus features.
   • How much base-game RTP is reduced to compensate?
3. This would prevent the illusion of added value and help players make informed choices.
4. Since persistence wasn’t strongly affected by free spins, regulators might find greater impact by focusing on other slot features, such as:
   • Losses Disguised as Wins (LDWs), which distort players’ perception of success.
   • Near wins, which create false expectations of being “close” to a jackpot.

Instead of outright bans, regulators could consider:

• Limiting bonus round frequency to reduce overexposure.
• Restricting audiovisual intensity (music, flashing graphics) that heightens excitement.
• Mandating player information prompts showing how free spins work mathematically.

Implications for Research and Industry

• The persistence-measuring task developed in this thesis is a new tool that can be applied to other slot-machine features.
• The findings highlight the importance of studying interaction effects — how free spins combine with jackpots, sound effects, or LDWs to shape player behavior.
• For the industry, this research suggests that free spins enhance enjoyment and player preference; however, casinos that rely too heavily on them may not be increasing long-term engagement as much as expected.