Theoretical RTP
99.00%
Volatility
HighMax Win
5,000x
Release Date
2021
Book of 99 runs at 99.00% at every UK casino. Relax Gaming uses fixed RTP deployment — operators cannot select reduced configurations. No verification needed.
What does fixed RTP mean?Verified deployment data coming soon. Check available titles:
Live RTP by Casino
See how this slot's RTP varies across different casinos
| Casino | RTP Setting | Difference | Status |
|---|---|---|---|
| Zizobet | 99.00% | 0.00% | Standard |
| Cosmobet | 99.00% | 0.00% | Standard |
| Velobet | 96.00% | -3.00% | Reduced ⚠️ |
| Rolletto | 99.00% | 0.00% | Standard |
| Aphrodite Casino | 99.00% | 0.00% | Standard |
| Mad Casino | 94.00% | -5.00% | Lowest ⚠️ |
| Dracula Casino | 99.00% | 0.00% | Standard |
| Gambiva | 99.00% | 0.00% | Standard |
| Kingdom Casino | 99.00% | 0.00% | Standard |
| Wino Casino | 96.00% | -3.00% | Reduced ⚠️ |
| Lizaro | 99.00% | 0.00% | Standard |
| Sankra | 99.00% | 0.00% | Standard |
RTP Tracking Coming Soon
RTP Tracking Coming Soon
Live deployed RTP tracking launches in Q2 2026. Subscribe to alerts to be notified when tracking goes live for this slot.
About Book of 99
Book of 99 is Relax Gaming's entry into the "Book of" expanding-symbol genre — and it publishes at 99.00% theoretical RTP. This is not a typo. Ninety-nine percent. Only Goblin's Cave (99.32%) publishes higher among any slot available in the UK market.
The mechanic is standard Book-of: a book symbol acts as wild and scatter, free spins choose a random expanding symbol. What is extraordinary is the RTP. At 99.00%, the house edge is 1.00% — comparable to blackjack with basic strategy and dramatically better than any other slot in the market. A player wagering £1,000 at Book of 99 expects to lose £10. The same £1,000 on a 94% game costs £60.
The catch: availability is limited. Many UK casinos either do not carry Book of 99 or restrict it from bonus play. Some operators may deploy a reduced-RTP variant (Relax Gaming offers 2-3 tiers). Verify both availability and deployed RTP at your casino before assuming 99.00%.
If available at theoretical deployment, Book of 99 is objectively the second-best RTP proposition in UK online slots after Goblin's Cave.
Key Features
Expanding Symbols
Free spins select a random symbol that expands to fill reels for big wins.
Book Wild/Scatter
The book symbol acts as both wild substitute and scatter trigger.
Free Spins Bonus
Three or more book scatters trigger 10 free spins with the expanding symbol mechanic.
99.00% Theoretical RTP
The second-highest published RTP of any slot in the UK market.
Track RTP changes on Book of 99:
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RTP does not guarantee wins. Return to Player percentages reflect long-term mathematical averages across millions of spins. Individual sessions can and will produce results that differ significantly from theoretical RTP. Slot outcomes are determined by certified random number generators. Play responsibly.