Last updated: May 2026. RTP behaviour modelled across 5,000 demo spins per featured AU casino during April-May 2026, plus reference to the official Relax Gaming math sheet.
99% RTP. That's the number. It's printed on every slot review of this game, plastered across every Relax Gaming marketing asset, and quoted by every YouTube reviewer who covers Book of 99. And it's actually accurate — Book of 99 carries the highest RTP of any mainstream video slot in regulated markets. But what does "99% RTP" actually mean for your session, your bankroll, your expected wins? This article is the one to read if you've ever wondered whether a 99% RTP pokie is mathematically better, or whether it's marketing — and how to make sure you're playing the certified 99% variant when you click "spin".
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What 99% RTP actually means
Return to Player (RTP) is the long-term average percentage of total bets that a slot returns to players as winnings. A 99% RTP means: across the entire population of every spin ever played on Book of 99, players collectively get back 99 cents for every dollar wagered.
The casino keeps the other 1 cent. That's the house edge.
For comparison, here's where Book of 99 sits in the industry:
| Slot | RTP | House edge per A$1 spun |
|---|---|---|
| Book of 99 (Relax) | 99% | A$0.01 |
| Mega Joker (NetEnt) | 99% (with optimal play) | A$0.01 |
| Blood Suckers (NetEnt) | 98% | A$0.02 |
| Jackpot 6000 (NetEnt) | 98.86% (with optimal play) | A$0.011 |
| Book of Dead (Play'n GO) | 96.21% | A$0.0379 |
| Sweet Bonanza (Pragmatic) | 96.51% | A$0.0349 |
| Book of Ra Deluxe | 95.1% | A$0.049 |
| Average online slot | 96% | A$0.04 |
| Average land-based pokie (AU) | 88-90% | A$0.11 |
The gap between Book of 99 and the average online slot is 3 percentage points — equivalent to a 75% reduction in the house edge. The gap between Book of 99 and the average Australian land-based pokie is 9-11 percentage points — equivalent to a ~90% reduction.
The compounding effect on your bankroll
A single spin's RTP difference looks tiny (A$0.03 vs A$0.04 = a one-cent gap). But spins compound. Here's what 99% vs 96% looks like across realistic session lengths at a A$1 bet:
| Spins | Book of 99 (99% RTP) expected return | 96% RTP slot expected return | Difference |
|---|---|---|---|
| 100 | A$99 | A$96 | A$3 |
| 500 | A$495 | A$480 | A$15 |
| 1,000 | A$990 | A$960 | A$30 |
| 5,000 | A$4,950 | A$4,800 | A$150 |
| 10,000 | A$9,900 | A$9,600 | A$300 |
Over 5,000 spins (a realistic year of casual weekly play at A$1 bets), Book of 99's higher RTP saves you roughly A$150 compared to a typical 96% slot.
Against a land-based pokie at 88% RTP, the same 5,000 spins at A$1 would expect to lose A$600. Book of 99 loses A$50. That's a A$550 swing for the same volume of play.
What 99% RTP does NOT mean
This is the part where new players get confused. 99% RTP does not mean:
1. "I will win 99% of the time." Hit frequency is independent of RTP. Book of 99 has ~23% base-game hit frequency — only about one in four spins wins anything. The 99% comes from the size of payouts when they hit, not from the frequency of payouts.
2. "Every A$100 I deposit, I get back A$99." No. RTP is an average across millions of spins. Your individual A$100 session can return anywhere from A$0 (you lost it all) to thousands (you hit a big bonus). RTP only emerges over very long sample sizes.
3. "99% RTP means it's a profitable game to play." Slightly tricky one. The expected value of every spin is still negative (-1% per spin on average). You're expected to lose, just less than at a 96% slot. The game is not "profitable" — it's "less unprofitable than average".
4. "99% RTP slots pay out faster." No. Spin speed is independent. RTP affects how much comes back; it doesn't affect when.
5. "If I see a long dry stretch, the game is 'due' to pay out." False — gambler's fallacy. Each spin is independent. A 50-spin dry stretch doesn't make the next spin more likely to hit.
Why 99% RTP works for advantage players (and what that means for you)
Advantage players — the kind who scour the slot landscape for value — care deeply about RTP because bonuses and promotions stack against RTP. If you're running a welcome offer with 30× wagering on a A$100 deposit, you need to spin A$3,000 of volume to convert the bonus to withdrawable cash.
At 96% RTP, your expected loss across that A$3,000 of volume is A$120. The bonus has to be worth more than A$120 for the play to be EV-positive.
At 99% RTP, your expected loss across the same volume is A$30. The bonus only has to be worth more than A$30 to be EV-positive.
This is why Book of 99 is a favourite for clearing wagering on casino welcome offers (where the game contributes 100% to wagering, which it does at most casinos). You complete the wagering with less expected loss than on any other mainstream slot.
Important catch: many casino welcome offers exclude or reduce contribution for high-RTP games specifically because of this. Check the bonus terms. If Book of 99 contributes only 50% (or 0%) to wagering, the EV argument collapses.
How to verify you're playing the 99% variant
Relax Gaming publishes Book of 99 in multiple RTP builds:
| Variant | Where deployed |
|---|---|
| 99% | Default — MGA-regulated, most EU markets, the four featured AU casinos |
| 96% | Some less-regulated jurisdictions |
| 94% | Used in jurisdictions with looser RTP-disclosure rules |
| 92% | Rare; lowest deployed variant |
Casinos choose which variant to deploy. The visual game is identical — same Orpheus, same expanding symbol, same 10 paylines. Only the math underneath differs.
Verify before you spin real money:
- Open Book of 99 in the casino lobby.
- Click the info icon (i) in the bottom-left corner of the game.
- Scroll to the RTP field.
- Confirm it reads 99%.
If it reads anything lower, close the game. You're playing a worse version of the same product.
All four featured casinos (Vegasnova, Joe Fortune, GreatSlots, CasinoRocket) run the 99% variant at the time of our last verification in May 2026. Unknown offshore brands sometimes run reduced variants — verify yourself before depositing.
Where 99% RTP doesn't save you
1. Bad bankroll management. A A$50 bankroll at A$5 stakes lasts ~12 spins. 99% RTP doesn't matter if you flame out before the math has a chance to work.
2. Wrong stake size for the variance. Book of 99 is high volatility. The 99% RTP is delivered through bigger payouts in free spins. If you're stake-sized to last only 100 spins, you may never trigger a bonus, and the high RTP delivers you nothing in that session. The 12,075× max-win path only opens once Orpheus is selected as the expanding symbol — and that requires bankroll patience.
3. Casinos that limit wagering contribution. If the casino's terms say Book of 99 contributes only 50% to wagering, your effective RTP for bonus-clearing purposes is 49.5%, not 99%.
4. Chasing losses. Every spin is independent regardless of RTP. Doubling your stake after losses just doubles the variance — it doesn't shift the math in your favour.
5. Playing the wrong variant. If you're playing the 92% variant without knowing, you're at a 8% house edge — worse than most pokies in the entire market.
Honest expectations for a session
Here's what a realistic Book of 99 session looks like at a A$100 bankroll, A$0.50 bets:
- Expected total volume: A$200-300 of spins before bankroll exhausts (assuming average variance).
- Expected bonus triggers: 1-2 (at ~1 in 220 spin rate).
- Most likely session outcome: small loss, maybe A$20-40.
- Best-case session outcome: Orpheus expanding symbol on a bonus round → 500-2,000× hit → A$250-1,000 win.
- Worst-case session outcome: zero bonus triggers, slow base-game drain → bankroll gone.
The 99% RTP means your expected loss is roughly A$3 per A$300 spun. The high volatility means your actual session outcome can vary wildly around that expectation.
Spin the highest-RTP mainstream pokie▶ Play Book of 99 · 🎁 Welcome Bonus
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Quick FAQ
Is 99% RTP really the highest of any mainstream slot? Yes, in the modern video-slot category from Tier-1 studios. Mega Joker (NetEnt) hits 99% with optimal supermeter play, but that's a niche fruit-machine title with active strategy required.
Does the casino have any way to reduce the RTP further? Only by deploying a lower RTP variant. The 99% variant is locked at 99%; the casino can't dial it down within that build.
Does the RTP change during free spins? No — the 99% applies across all phases of the game, base game and bonus combined. Free spins deliver higher RTP individually (because that's where the value lives) but the weighted average across base + bonus is 99%.
If I play 10,000 spins at A$1, will I be at -A$100? That's the expected value, but actual variance means you could be anywhere from -A$2,000 to +A$5,000 in a 10,000-spin sample. The 99% emerges over millions of spins, not tens of thousands.
Are there slots with higher than 99% RTP? A handful of niche games (some Mega Joker variants, some video poker games with optimal strategy) approach or exceed 99% — we compare Book of 99 to all of them. Among mainstream video slots, Book of 99 leads.
Why don't more studios make 99% slots? Margin. A 4% house edge generates four times the revenue of a 1% house edge on the same volume. Relax Gaming made Book of 99 as a marketing piece more than a profit center.
Should I switch all my play to Book of 99? It depends on what you enjoy. If you like high-variance book slots, yes. If you prefer low-variance slots with frequent small wins, no — different game style.
About this RTP analysis
Modelled across 5,000 demo spins per featured AU casino during April-May 2026. Reference math drawn from the Relax Gaming official product page and cross-checked against MGA-published certification documents.
Gambling responsibly. 99% RTP is the best math you'll find — and it still doesn't make slots profitable. Pokies are entertainment, not investment. Set deposit limits before depositing. AU support: gamblinghelponline.org.au · BetStop · 18+ only.
Further Reading
Related reading in this guide: