Bonus Round

Bonus rounds are where slot machines transform from simple spinning reels into interactive experiences with massive win potential. These special features—triggered by scatter symbols or random events—offer mechanics impossible in base gameplay: unlimited multipliers, expanding wilds, pick-and-click prizes, and cascading wins. Most modern slots concentrate 60-80% of their theoretical return within bonus rounds, making them the primary driver of both big wins and the game's overall volatility.

How Bonus Rounds Work
Types of Bonus Rounds
Bonus Round Math
Triggering Bonuses
Bonus Buy Feature
Evaluating Bonus Potential
Common Myths

How Bonus Rounds Work {#how-it-works}

The Basic Concept

Bonus rounds are separate game states with enhanced mechanics:

Aspect	Base Game	Bonus Round
Win frequency	Regular	Often higher
Win potential	Limited	Enhanced
Special features	Few	Many
Multipliers	Rare	Common
Duration	Unlimited	Limited (usually)

Trigger Mechanisms

Trigger Type	How It Works
Scatter symbols	Land 3+ scatters anywhere
Bonus symbols	Land bonus symbols on specific reels
Random trigger	Mystery trigger any spin
Accumulator	Fill meter over multiple spins
Buy feature	Pay to instantly trigger

Bonus Round Flow

Trigger: Meet activation requirements
Award: Receive spins/picks/starting multiplier
Play: Complete bonus with enhanced mechanics
Settlement: Total wins credited to balance
Return: Back to base game

Types of Bonus Rounds {#types}

Free Spins

The most common bonus type—spin without wagering from balance:

Feature	Description
Spin count	Typically 8-20 free spins
Multiplier	Often starts at 1x, can increase
Retrigger	Additional scatters add more spins
Enhanced	Special symbols, expanded wilds

Examples: Book of Dead (10 free spins with expanding symbol), Starburst (up to 3 re-spins with expanding wilds)

Pick and Click

Interactive games where player choices reveal prizes:

Variant	Mechanic
Prize pick	Choose items to reveal cash/multipliers
Avoid the bomb	Keep picking until hitting terminator
Trail/ladder	Advance through levels for bigger prizes
Match	Find matching pairs for rewards

Examples: Rainbow Riches (Pots of Gold pick), Fishin' Frenzy (fish selection)

Wheel Bonuses

Spin a wheel to determine prize:

Feature	Description
Segments	Different prizes on wheel sections
Multipliers	Some segments multiply total
Jackpots	Often linked to progressive
Re-spins	May award additional wheel spins

Examples: Mega Fortune (three-tier wheel), Crazy Time (various wheel segments)

Cascading/Avalanche Features

Winning symbols disappear, new symbols fall:

Mechanic	Detail
Initial win	Matching symbols removed
Cascade	New symbols drop from above
Multiplier	Often increases per cascade
Chain	Continues until no new wins

Examples: Gonzo's Quest (increasing multipliers per cascade), Sweet Bonanza (tumble feature)

Hold and Spin

Special symbols lock in place for respins:

Feature	Description
Trigger	Land minimum special symbols
Respins	Usually 3 respins to start
Lock	Specials stay, respins reset on new symbol
Prizes	Symbols reveal cash, jackpots, or features

Examples: Lightning Link (hold and spin), Wolf Gold (Money Respin)

Multi-Level Bonuses

Progress through stages for bigger rewards:

Level	Typical Reward
Level 1	Small multipliers/prizes
Level 2	Medium rewards
Level 3+	Maximum potential

Examples: Immortal Romance (four different free spin modes unlock progressively)

Expanding Features

Features that grow during bonus:

Type	Mechanic
Expanding reels	Grid grows during bonus
Expanding wilds	Wilds cover entire reels
Expanding multipliers	Multiplier increases throughout
Expanding ways	More paylines/ways added

Examples: Big Bass Bonanza (expanding fisherman collection), Reactoonz (expanding wild cluster)

Bonus Round Math {#math}

RTP Distribution

\text{Total RTP} = \text{Base Game RTP} + \text{Bonus RTP}

Typical distribution for a 96% RTP slot:

Component	RTP Contribution	Percentage
Base game	38.4%	40% of total
Bonus rounds	57.6%	60% of total
Total	96%	100%

Bonus Contribution Calculation

\text{Bonus RTP Contribution} = P(\text{Trigger}) \times \text{Average Bonus Win}

Example:

Trigger probability: 1 in 150 spins (0.67%)
Average bonus win: 90x bet
Bonus RTP contribution: 0.0067 × 90 = 60.3%

Expected Bonus Value

\text{E[Bonus]} = \sum_{i=1}^{n} P(i) \times \text{Win}(i)

Outcome	Probability	Win	EV Contribution
Minimum (20x)	30%	20x	6x
Average (80x)	55%	80x	44x
Big win (200x)	12%	200x	24x
Max win (5000x)	3%	5000x	150x
Total EV			224x (theoretical)

Note: Actual distributions are game-specific

Trigger Probability

P(\text{3 Scatters}) = \binom{5}{3} \times p^3 \times (1-p)^2

Where p = probability of scatter on each reel. Typical trigger rates:

Trigger Frequency	Spins Between	Considered
1 in 80	80 spins	Frequent
1 in 150	150 spins	Average
1 in 250	250 spins	Rare
1 in 400+	400+ spins	Very rare

Variance Impact

Bonus rounds dramatically increase variance:

\text{Total Variance} = \sigma_{base}^2 + \sigma_{bonus}^2 \times P(\text{bonus})

Slot Type	Base Variance	Bonus Variance	Total Feel
Low volatility	Low	Medium	Steady wins
Medium volatility	Medium	High	Balanced
High volatility	Low	Very high	Bonus-dependent

Triggering Bonuses {#triggering}

Scatter Requirements

Scatters	Common Result
3 scatters	Minimum trigger (10 spins typical)
4 scatters	Extended bonus (15 spins typical)
5 scatters	Maximum spins (20+ typical)
6+ scatters	Rare, huge bonus (25+ spins)

Retrigger Mechanics

Landing scatters during bonus extends it:

Retrigger	Typical Award
2 scatters	+2-3 spins
3 scatters	+5-10 spins
4+ scatters	+10-15 spins

Some slots cap retriggers; others allow unlimited extensions.

Scatter Positions

Requirement	Description
Anywhere	Most common—position doesn't matter
Specific reels	Only middle reels count (1-3-5 or 2-3-4)
Adjacent	Scatters must be on consecutive reels
Left to right	Must start from reel 1

Bonus Trigger Tips

Strategy	Reality
Change bet before bonus	No effect—RNG is instant
Play longer sessions	No effect—each spin independent
Switch slots if no bonus	No effect—no "due" mechanic
Higher bets = faster triggers	No effect on probability

Bonus Buy Feature {#bonus-buy}

How Bonus Buy Works

Pay a premium to skip directly to the bonus round:

\text{Buy Cost} = \text{Bet} \times \text{Multiplier (typically 80-100x)}

Example	Bet	Buy Cost
Standard buy	$1	$80-100
Enhanced buy	$1	$200-500
Super buy	$1	$500-2000

Bonus Buy Economics

Factor	Natural Trigger	Bonus Buy
Cost	Variable (average 100-150 bets to trigger)	Fixed (80-100x typically)
Time	Hours potentially	Instant
RTP	Full game RTP	Often 1-2% lower
Variance	Lower (includes base game)	Maximum

RTP Comparison

Method	Typical RTP
Natural play	96%
Standard bonus buy	94-95%
Enhanced bonus buy	93-95%

Bonus Buy Variations

Type	Description
Standard	Buy basic bonus entry
Enhanced	Buy bonus with extra feature (higher multiplier start)
Super	Buy best possible bonus setup
Random	Buy random bonus tier

Legal Restrictions

Region	Bonus Buy Status
UK	Banned (as of October 2021)
Sweden	Restricted
Germany	Restricted
Malta-licensed	Allowed
Curacao-licensed	Allowed

When to Consider Bonus Buy

Use Case	Recommendation
Testing a slot's bonus	Acceptable (demo mode)
Entertainment/excitement	Personal choice
Optimal EV	Never (lower RTP)
Bonus clearing	Often prohibited in terms

Evaluating Bonus Potential {#evaluation}

Key Metrics

Metric	What It Tells You
Average bonus win	Expected return per bonus
Max win in bonus	Upside potential
Trigger frequency	How often you'll reach bonus
Retrigger potential	Can bonus extend significantly
Multiplier ceiling	How high multipliers can go

Bonus Quality Indicators

Feature	Positive Sign
Unlimited multiplier	High ceiling
Sticky wilds	Consistent wins during bonus
Retrigger available	Extended play possible
Win multipliers	Exponential potential
Progressive features	Bonus improves as it plays

Red Flags

Feature	Concern
Fixed low multiplier	Capped potential
No retrigger	Fixed short bonus
Pick to end	Can terminate early
Complex mechanics	May hide poor returns

Comparing Bonus Quality

Slot	Bonus Type	Max Win	Average	Volatility
Book of Dead	Expanding symbol FS	5,000x	80x	High
Sweet Bonanza	Tumble + multipliers	21,175x	100x	Very high
Starburst	Expanding wild respins	500x	15x	Low
Gonzo's Quest	Cascading multipliers	2,500x	50x	Medium

Bonus Round Strategy {#strategy}

Game Selection

Priority	Choose Slots With
Big win potential	High max multiplier bonuses
Consistent returns	Frequent small bonuses
Entertainment	Interactive pick features
Low risk	Low volatility bonuses

During Bonus Rounds

Tip	Explanation
No decisions affect outcome	Results are predetermined by RNG
Enjoy the experience	Entertainment value is real
Note the mechanics	Learn what makes good bonuses
Track your results	Understand actual vs. expected

Bankroll for Bonus Hunting

\text{Minimum Bankroll} = \text{Bet Size} \times \text{Average Spins to Trigger} \times 2

Trigger Rate	Bet	Minimum Bankroll
1 in 100	$1	$200
1 in 200	$1	$400
1 in 300	$1	$600

Session Planning

Factor	Consideration
Target bonuses	How many bonuses do you want?
Bankroll needed	2-3x expected cost to trigger
Time available	Slow slots = fewer triggers
Loss limit	Accept possibly 0 bonuses

Common Myths {#myths}

Myth 1: Bonuses Are "Due" After Dry Spell

Reality: Each spin has identical trigger probability regardless of previous results. After 500 spins without a bonus, the next spin has the same odds as after 5 spins.

P(\text{Bonus on spin 501}) = P(\text{Bonus on spin 1}) = \frac{1}{150} \text{ (example)}

Feature	Detail
Variety	Thousands of unique mechanics
Complexity	Multi-level, progressive features
Bonus buy	Often available
RTP disclosure	Usually published

Land-Based Slot Bonuses

Feature	Detail
Variety	More limited selection
Complexity	Often simpler mechanics
Bonus buy	Rarely available
RTP disclosure	Usually hidden

Notable Differences

Aspect	Online	Land-Based
Innovation	Cutting-edge	Conservative
Max wins	Higher (50,000x+)	Lower (2,500x typical)
Frequency	Varies widely	Often more frequent
Jackpots	Progressive common	Less common

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Bonus Round

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