Myth check · RTP and Odds
How Slot Games Work: From Random Number to Reel Stop
One spin traced from the random number to the reels: how the paytable fixes RTP, why near misses are banned, and what regulators say a slot must pay back.
SlotFacts Editors · Nov 9 2026
A slot game works by drawing a random number for every spin, turning that number into a set of reel stops, and paying whatever the paytable says those stops are worth. The spinning reels you watch are a picture of a result that was fixed the moment you pressed spin. Nothing about the last spin, the time of day or how long you have been playing changes the odds of the next one, and regulators put that in writing.
To show how slot games work in practice, we follow one spin from the generator to the screen, then show where the payback figure comes from.
What happens in one spin, from random number to reel stop?
Each spin takes a fresh number from a random number generator (RNG), scales it to the positions on each reel, and reads the matching symbols off the reel strip. The UK Gambling Commission, whose technical standards are the clearest public statement of these rules (as of May 2024), requires that the random inputs are mapped according to pay tables and the game's stated probabilities.
Step by step, a regulated spin looks like this:
| Stage | What happens | What the rules say |
|---|---|---|
| Draw | The RNG produces a number | Numbers are used in the order they are received |
| Scale | The number is cut down to the size of each reel | Scaling must keep the generator's uniform, unpredictable qualities |
| Map | Each scaled value points to a stop on a reel strip | The mapping follows the prevailing probabilities and paytable |
| Pay | The symbols on the payline are checked against the paytable | The win, if any, is paid as the paytable lists it |
| Show | The reels animate and stop where the number said | No swapping the result for a different-looking loss |
The order matters. A game cannot draw a few numbers and keep the one it likes, because a number that comes out of the generator has to be used.
How does the paytable fix a slot's RTP and hit rate?
The paytable and the reel strips together decide the return to player (RTP) before anyone spins. Take every possible combination of stops, multiply its chance of landing by what it pays, add the lot up, and you have the RTP. Count only the combinations that pay anything and you have the hit rate.
That is why a game with the same symbols can be built at different RTPs: the maker changes how many stops each symbol gets on a strip, or what each line pays, and the sum moves. Our guide on what slot has the highest RTP shows how far that sum usually sits from a full return, and the piece on whether a slot machine odds calculator can work explains why you cannot rebuild the sum from outside the game.
Once a game is live, its rules, payouts and outcome probabilities cannot change while it is open for play, except as its own rules already provide. In the UK, the operator must also show the house edge before you gamble, along with either the RTP percentage or win probabilities. If a site serving Nigerian players hides that figure, treat it as a gap worth noticing before you stake naira on the game. More on reading those figures sits in our RTP and odds guides.
Can a slot tighten up, loosen up or owe you a win?
No. Under the UK standards, adaptive, or compensated, games are not permitted: a slot may not shift its odds because it has paid out a lot, or because you have been losing for an hour.
This is the mechanical reason the "it just paid, so leave it" and "it is due" tips fail. Each spin is a new draw against the same fixed mapping. We take the popular version of this claim apart in our piece on how to win at a slot machine, and the answer is the same for any regulated title.
Why do near misses show up so often?
Near misses show up because the reel strips put symbols where they land next to each other, not because the game is teasing you on purpose. Regulators draw a hard line here: a game may not substitute a losing result with a near miss to make a win look closer than it was.
So the stops you see must be the stops the number picked. Two jackpot symbols and a blank one row off is just another losing combination, with the same weight in the RTP sum as any other loss.
Reels and video slots: does the screen change anything?
Whether a slot spins physical reels or draws them on a screen, the result comes from the same chain: random number, mapping, paytable. Video slots add features such as tumbling symbols, bonus rounds and free spins, but each feature is one more set of outcomes inside the same fixed sum, mapped under the same rules. The graphics decide how a result looks. They do not decide what it is.
How much does a slot actually pay back?
Legal minimums sit well below what games pay in practice. Nevada sets a 75 percent theoretical payout standard for gaming devices (as of February 2022), meaning machines there must return at least 75% of all money wagered.
What casinos keep in practice is much smaller and has crept up. A UNLV study reported in January 2026 found the average statewide hold reached 7.1% in 2025, against 6.55% in 2004. Hold is the share of money wagered that the machines kept, so on average a little more of every bet stays with the house than it did in 2004.
None of that is a forecast for your session. RTP and hold are long-run averages across an enormous number of spins. Over an evening, volatility decides whether your balance goes up or down, and the house edge decides which way it drifts the longer you play.
Quick questions
How do online slots decide who wins?
A random number generator picks each result, and the game maps that number to reel stops using fixed probabilities and a paytable. In regulated markets the numbers must be used in the order they come out.
Are slot machines truly random?
The draw is random, but the odds are not even: the maker sets how often each symbol appears and what it pays. The randomness decides which spin wins. The design decides how much the game returns over time.
Should you play a slot machine that just paid out?
It makes no difference. Regulated slots cannot adjust their odds after a payout, so the next spin has the same chances as the last.
What's the best time to play slots?
There is none. The rules, payouts and probabilities of a regulated game cannot change while it is available, so morning, midnight or payday all face the same odds.
Is slot luck or skill?
Luck, for the result of each spin. The only choices that matter are which game you pick, how much you stake and when you stop.
Sources
- UK Gambling Commission, RTS 7 Generation of random outcomes, 7 May 2024
- UK Gambling Commission, RTS 3 Rules, game descriptions and the likelihood of winning, 7 May 2024
- Nevada Gaming Control Board, Proposed amendments to Nevada Gaming Commission Regulation 14, 24 February 2022
- Covers, Nevada Slot Machines Gradually Paying Out Less, Study Finds, 21 January 2026
