Book of 99

Relax Gaming dropped Book of 99 back in May 2021, and honestly, it's a slot that still gets talked about for good reason. With a certified 99% return-to-player rate, this is one of the highest-RTP slots you’ll ever spin.

If you’re like most players, you’ve probably never actually hit “spin” on a modern slot with returns this high. Book of 99 stands out in a sea of average games, and it’s not just about the numbers—it’s about the way it plays. Before diving in, check if your casino lets you use a welcome bonus here; stretching your bankroll on a high-volatility slot is just smart.

The game sits on a familiar 5x3 grid, rocking 10 fixed paylines and a Greek mythology vibe. What really makes it tick? There’s a dual free spins entry system and a 99-book collection meter that slowly builds tension as you play.

AskGamblers rates Book of 99 at 8.9 out of 10. Players love it, and that’s not just hype. BigBookofSlots gives it 8.9/10 stars too, but they’re quick to remind you: 99% RTP is a return figure, not a guarantee you’ll walk away a winner every time.

Quick Verdict And Key Numbers

Book of 99’s reputation comes from pure math, not flashy animations or over-the-top features. That 99% RTP headline grabs attention, but the high volatility means the ride isn’t always smooth.

Expect cold spells before the free spins finally hit. Relax Gaming really dialed in the numbers here, and if you can snag a welcome bonus, it’s a great way to test the waters without risking too much up front.

What This Slot Is Best Suited To

This one’s not for everyone. It’s perfect for:

• Patient, session-focused players who aren’t afraid of a long grind and can manage their budget

• Fans who value long-term returns over a steady drip of small wins

• Slot regulars who understand high-volatility math and accept that variance is the price for bigger potential

• Anyone who loves “Book” slots but wants more than just standard free spins—something with a real layer of depth

If you’re a casual player or you get bored without frequent wins, this probably isn’t your game. It’s just not built for low-stake, quick-hit fun.

Third-Party Community Signals

AskGamblers and BigBookofSlots both land at 8.9 out of 10 for Book of 99. They’re upfront about the volatility, and honestly, it’s a big part of the experience. Most reviews zero in on that unique collection meter—it’s the mechanic that keeps you coming back.

So far, there’s no confirmed max-multiplier win tracker from the big community sites. If you’re chasing a leaderboard, you’ll have to go by what Relax Gaming lists as the ceiling.

Industry Benchmark Snapshot

Let’s see how Book of 99 stacks up against the competition.

Core Specifications At A Glance

How The Base Game Works

Book of 99’s base game is refreshingly simple. The 99% RTP hangs over every spin, but it’s the wild symbols that really drive the action.

Reels, Layout, And Fixed Paylines

Here’s the setup: 5 reels, 3 rows, and 10 fixed paylines. Wins always pay left to right, starting from reel one. The layout mirrors Book of Dead and Book of Ra, and that’s no accident—it’s what slot fans expect from a classic “Book” game.

Relax Gaming didn’t mess with the grid; instead, they tweaked the math model. You get the comfort of a familiar setup but with way higher returns if you stick with it.

With 10 paylines, you know exactly which lines are in play. There’s no toggling, no “ways” mechanic, no cluster pays—just classic lines and pure anticipation.

Symbols, Paytable, And Winning Logic

The symbols split into two clear camps. Here’s how it breaks down on the paytable:

High-value symbols (Greek gods):

• Four god characters—think Lamia and the like—paying from 2-of-a-kind upwards

• Payouts range from 0.50x to 500x your bet for five of a kind

• The top god symbol slaps down 500x for five across a line

Low-value symbols (card royals): These are your standard A, K, Q, J, 10.

• They only pay from 3-of-a-kind up

• Payouts run from 0.5x to 15x for five across—these don’t move the needle much for variance

The Book symbol:

• This one’s both a wild and a scatter. It’s the key to unlocking the real fun.

• It fills in for any regular symbol during base play

• Land three or more anywhere and you trigger free spins—this is where it gets exciting

• Every book wild you land also feeds the collection meter, building toward that secondary bonus

The paytable leans hard toward those four god symbols. Chasing card royals? Not worth your time here—the big wins live in the premiums.

Theme And Visual Identity

Book of 99 dives into Greek mythology, with crisp visuals and a moody, cinematic intro focused on the golden book. The whole vibe is darker and more intense than most book slots out there.

Background music hums along with a battle-ready energy. It fits the mythic theme and, thankfully, never gets annoying or drowns out the anticipation as the reels come alive.

What Makes The Bonus Cycle Different

Book of 99 gives you not just one, but two routes to the all-important bonus. There’s the classic free spins trigger, and then there’s the wild collection feature—honestly, this is the kind of mechanic that gets my slot-obsessed heart racing.

Most players chase those free spins, but the meter? That’s where Book of 99 breaks away from the “Book of” clones. The anticipation just builds and builds as you watch those wilds stack up.

The free spins round is the real star here, no question. It’s not just another bonus—it actually changes how you think about your whole session.

Free Spins Triggered By Scatters

Land 3 or more Book symbols (the scatter) anywhere on the reels and you’re in for 10 free spins at your current stake. Before those spins start, the game picks a random symbol to become the expanding symbol for the whole round.

When that chosen symbol hits, it stretches to fill the entire reel—watching those reels fill up never gets old. The best part? It pays on all 10 lines at once if you line it up right.

This is where the magic happens. If you manage to land the right expanding symbol across enough reels, you can actually hit the 5,000x max payout. Not saying it’s easy, but the potential is there—and the adrenaline when you see those reels light up? Unmatched.

The 99-Book Collection Meter

This meter is what turns Book of 99 into a marathon, not a sprint. There’s a counter next to the reels, starting at 99.

Each Book Wild that lands knocks the meter down by one. When you finally hit zero, boom—the free spins bonus triggers automatically.

Unlike most slots, this meter keeps ticking down across your whole session. It doesn’t reset if you take a break or change your bet.

If you’re in it for the long haul, you’ve got a real edge. The meter is a slow burn, but it guarantees you’ll see the bonus if you stick around long enough. No praying for a lucky streak—just steady progress.

Average-Bet Rule On Meter Bonuses

Here’s where it gets a bit technical, but trust me, it matters. When the meter triggers free spins, the game calculates your average bet across the whole session and uses that as your bonus stake.

This is different from the scatter-triggered bonus, which always uses your current bet. If you start at $1.00 a spin and ramp up to $5.00 right before the meter hits, you don’t get the $5.00 bonus—just the average across your session.

So, if you’re chasing the meter, keep your bets steady. Don’t try to game the system by cranking your stake at the last second. I’ve seen plenty of players get burned by that.

Expanding Symbol Behavior In Free Spins

In both the scatter and meter-triggered bonuses, one symbol becomes “the one.” When it lands during free spins, here’s what you’ll experience:

• It expands to fill the whole reel—all three rows, no hesitation.

• Payouts hit across all 10 paylines if you make the connection.

• When you land expanding symbols on multiple reels at once, that’s when the big wins roll in. The rush is real.

The mechanic is identical for both bonus paths. The only thing that changes is how the stake is set—average bet for the meter, current bet for scatters. Just something to keep in mind if you’re strategizing.

RTP, Volatility, And Session Value

The math in Book of 99 is wild—in a good way. There’s nothing else like it, honestly.

Let’s talk about that 99% RTP. On paper, it’s a dream. But what does it actually mean for your session? And how does the high volatility play into it?

What 99% RTP Really Means

RTP is just a long-term average, not a promise for your next 100 spins. With 99% RTP, the game pays back $99 for every $100 wagered—over millions of spins, not in your afternoon session.

Compared to a 96% slot, the edge here is real, but you only feel it if you’re spinning for the long run. For high-volume grinders, that 1% house edge is a game-changer. For casual players, honestly, you might not notice much difference in just a few sessions.

Why High Volatility Still Matters

High volatility means you’ll have dry spells—sometimes long ones. Big wins are possible, but they’re rare, and you can burn through your bankroll before you even sniff the bonus.

Usually, high-RTP slots are slow, steady grinders (like NetEnt’s Mega Joker). Book of 99 flips the script: you get sky-high RTP and wild swings. If you love the thrill and can stomach the swings, this is your playground. If you’re risk-averse, maybe not.

Bankroll Fit And Stake Planning

Here’s how I’d approach a session on Book of 99:

• Minimum session bankroll: 100x your stake per spin—bare minimum, honestly.

• Comfortable session bankroll: 200x your stake per spin. Gives you breathing room for those dry streaks.

• Stake for the collection meter: Keep it consistent. Don’t get cute with last-minute bet jumps, or your average will tank your bonus value.

The $0.10 minimum bet makes it super accessible. At ten cents a spin, you can get a 200-spin session for just $20. Not bad for testing the waters or just enjoying a longer grind.

How It Compares With Similar High-RTP Titles

Book of 99 is the only high-volatility, high-RTP “Book of” slot out there. Book of Dead and Book of Ra have the same core mechanic, but their RTPs are way lower. Mega Joker matches the RTP but is a totally different beast—no expanding symbols, just old-school grind.

Demo Play, Similar Slots, And Overall Fit

If you’re new to Book of 99, try the demo first. With the collection meter, you really want to see how it ticks down and how both bonus paths play out before you risk any real cash.

How To Use The Demo Before Playing

You can find the Book of 99 demo on most review sites. It works perfectly on mobile, too—no clunky controls or weird lag.

When you’re testing, pay attention to a few things:

• Watch how the collection meter drops. Track how many base-game Wilds you hit every 50–100 spins. It gives you a sense of how long a session might last before the meter triggers.

• Notice the average-bet calculation. Keep your demo stake steady and see what the bonus pays when the meter fires. It’s eye-opening if you’re used to last-minute bet jumps.

• Trigger the scatter free spins at least once. See the expanding symbol in action—when you hit it on 2–3 reels at once, you’ll know why this mechanic is so beloved.

Don’t use the demo to judge short-term returns. A couple hundred spins won’t show you the real power of 99% RTP. That only comes out over thousands, even tens of thousands, of spins. But for getting a feel for the features? It’s perfect.

Closest Alternatives For Book-Slot Fans

Who Should Skip This Game

Book of 99 really isn't for everyone. If you fall into any of these categories, you might want to look elsewhere:

• Casual spinners who need regular wins to stay engaged. The hit frequency in the base game can be brutal, and cold streaks? Oh, they happen—a lot.

• Players craving complex, multi-layered bonus features. Honestly, the features are stripped down: just two ways to trigger 10 free spins with expanding symbols, and that's it.

• Short-session players. The collection meter only shines if you’re in for 100–200 spins or more. Anything less, and you’ll barely notice it.

• Anyone at a casino running a lower RTP version. Some operators dial the RTP down below 99%. Always check the in-game info panel—don’t take it for granted.

Pros, Cons, And Final Take

Four Reasons It Works

Four Reasons It May Not