How online slots work

Slots are the biggest game in online casinos and the least understood. The reels, sounds and near-misses are presentation. Underneath, every slot is a random number generator, a paytable and a set of rules about how often it pays and how much. Once you can read those three things, you can tell a gentle slot from a brutal one before you spin, see what a bonus will cost to clear on it, and know what the casino has chosen to keep. This guide covers it all, with the studios' own published numbers.

What happens when you press spin

A slot's random number generator (RNG) picks the result the moment you spin. The animation that follows just shows that result. Three things follow from that:

• Every spin is independent. A slot does not remember the last spin and is never "due" to pay.
• Near-misses mean nothing. Two scatters and a third just above the line is a display choice, not a close call.
• Speed does not change the odds. Turbo mode and quick stop only change how fast you see the outcome, and how fast you spend.

Paylines, ways and clusters

How a slot decides which symbols pay is its "pay mechanic". The common ones:

The ways count is just multiplication: symbols per reel multiplied across all reels. Four rows on five reels is 4^5 = 1,024 ways; five rows is 5^5 = 3,125. More ways does not mean a better game. The paytable is scaled to the mechanic, so a 117,649-way slot pays less per symbol combination than a 10-line slot.

Cluster and pay-anywhere games usually add tumbling (or cascading) reels: winning symbols disappear, new ones drop in, and one paid spin can chain into several wins.

RTP: the long-run return

Return to player (RTP) is the share of all money bet on a slot that it pays back over a very long run. The rest is the house edge.

Studios publish the RTP of each game. From their own game pages:

The RTP setting your casino chose

Here is what most players never see: many slots ship with several RTP versions, and the casino picks which one to run. Hacksaw Gaming's own page for Wanted Dead or a Wild lists four: 96.38%, 94.55%, 92.33% and 88.42%. Same graphics, same features, very different cost.

The lowest setting costs more than three times as much as the highest per dollar wagered (115.80 vs 36.20). The only way to know which one you are playing is the game's own info or help screen, which states the RTP at that casino. Check it before you play a slot for the first time at a new casino. Our RTP and volatility guide goes further, and highest payout casinos looks at which casinos publish their settings.

Volatility and hit frequency

Two slots with the same RTP can feel completely different. Volatility (also called variance) describes how the payback is spread:

• Low volatility: frequent small wins; the balance drifts down slowly.
• High volatility: long dry runs, rare large wins; most of the RTP sits in a few big bonus rounds.

Studios rate it on their own scales. Hacksaw rates Wanted Dead or a Wild 4 out of 5, with a maximum win of 12,500 times the stake. There is no industry-wide definition of "high", so compare within one studio's scale.

What volatility does to a session: on a high-volatility slot, most short sessions return less than the RTP, because the big wins that hold up the average are rare. A few sessions return far more. If you have C$50 for the evening, a low-volatility game makes it last; a high-volatility game gives a small chance at a big hit and a large chance of a short night.

Hit frequency is the share of spins that pay anything, including wins smaller than the stake. It is not the same as volatility: a slot can hit one spin in four and still be high volatility if most hits are tiny and the real money sits in the bonus.

Features that drive the payouts

• Free spins. Triggered by scatters. Book of Dead gives 10 free spins for three scatters, with one symbol chosen to expand across its reel for the whole feature. Sweet Bonanza gives 10 free spins for four to six scatters.
• Multipliers. Sweet Bonanza's multiplier symbols are worth 2x to 100x and add together at the end of a tumble sequence; Gates of Olympus multipliers reach 500x; Sugar Rush marks winning spots and doubles a spot multiplier up to 128x.
• Hold and win / respins. Wolf Gold's Money Respins start with six money symbols, reset to three respins with each new one, and pay a fixed Mega jackpot of 1,000 times the bet for filling all 15 positions.
• Jackpots. Fixed jackpots pay a set multiple; progressive jackpots grow with every bet. See jackpot slots.
• Maximum win. Many modern slots cap the total win per spin or bonus as a multiple of the stake, stated in the game rules.

Bonus buys

Many slots let you pay a fixed price, a multiple of your stake shown before you confirm, to start the bonus round at once. Two things to know:

• The buy's RTP can differ from the base game's; the game rules state it where the studio publishes it.
• Bonus buys concentrate volatility: you skip the base game and stake a large amount on one feature.

With a casino bonus active, most terms ban bonus buys or count the buy as a single spin at its full price. V.Vegas's terms say a bonus-buy counts as a spin subject to the per-spin cap; at that point one click breaks the max bet rule and can void the bonus.

Slots and casino bonuses

Slots are the game bonuses are designed for, because they count fully toward wagering at most casinos. Jackpot City's published terms count slots at 100%, but NetEnt slots at 50%, re-spin slots at 10% and progressive jackpots at 0%. Read the game weighting guide before choosing a slot to clear a bonus.

To estimate what clearing a bonus costs on a given slot, multiply the wagering by the house edge (100% minus RTP):

At typical wagering, the expected cost of clearing can exceed the bonus, and the RTP setting can decide whether the bonus is worth anything at all. Run the numbers with the wagering calculator, and read wagering requirements and free spins explained for the terms around them. Current offers sit on free spins bonuses.

What a session costs per hour

RTP turns into an hourly price once you count spins.

Spins per hour are illustrative; autoplay and turbo modes can push the count much higher. The quickest way to spend less is fewer, slower spins.

Reading a paytable

Every slot has a paytable and a rules screen, usually behind an "i" or menu icon. Five minutes there tells you more than an hour of spinning.

• Symbol values. Payouts are shown as multiples of the stake or of the line bet. Check which: a "500" on a 20-line game may be per line, which is 25 times the total stake.
• Feature triggers. How many scatters start the free spins, and whether the feature can retrigger.
• Maximum win. The cap on a single spin or feature, stated as a multiple of the stake.
• RTP. The setting this casino runs. If the screen lists several RTPs for different modes (base game, bonus buy, ante bet), each applies only to that mode.
• Malfunction clause. Every game voids pays and plays on a malfunction. This is standard wording, not a warning sign.

Myths worth dropping

"It's due." A slot that has not paid for a while is no more likely to pay on the next spin. Each result is independent.

"Bigger bets get better odds." On a standard slot the RTP is the same at every stake. Some jackpot games are the exception, and their rules say so.

"Casinos tighten slots at night." The RTP setting is chosen per game and per casino, not adjusted spin by spin. The help screen shows the setting in use.

"Autoplay plays worse." It plays exactly the same; it just plays faster, so you wager more per hour.

Choosing a slot

1. Check the RTP in the game's info screen at your casino; prefer the top setting.
2. Match volatility to your budget. Small budget, long session: lower volatility.
3. Read the paytable and max win so you know where the money sits.
4. With a bonus, check the weighting and max bet before the first spin.

Browse games on our slots page; casino reviews such as Jackpot City and V.Vegas list each casino's bonus terms for slots.

Where Canadians play slots

Provincial sites such as BCLC's PlayNow (B.C.), PlayNow Manitoba and Saskatchewan, Loto-Quebec and Atlantic Lottery offer online slots in their own provinces. Offshore casinos licensed abroad serve players outside Ontario and Alberta; provincial protections and self-exclusion do not reach them, so their own limit tools are what you rely on.

Set the price before you play

A slot is entertainment with a price per hour. The Lower-Risk Gambling Guidelines suggest no more than 1% of household income a month on gambling and no more than four days a month. Use deposit limits and session reminders in your casino account, and see the responsible gambling tools guide. Free, confidential help for your province is listed on our responsible gambling page.