How Online Slots Work: RTP, RNG and Volatility Explained

How online slots really work: random number generators, what RTP means, why volatility matters, and the law in Singapore, Malaysia and Thailand.

Quick answer: An online slot is a computer program. A random number generator (RNG) decides every result, and the game is designed to pay back less than players stake over time. That gap is the house edge. RTP describes the long-run average, not what will happen in your session.

What decides the result of a spin?

Modern slots do not depend on physical reels. A random number generator picks the outcome, and the reels on screen simply display it. Because software can give each symbol a different probability, a “near miss” can look much closer to a win than it really was. Earlier spins do not make a win “due”.

What does RTP mean?

RTP (return to player) is the percentage of all money staked that a game is designed to pay back as prizes. The UK Gambling Commission stresses that it is an average achieved over a very large number of plays, not each time a game is played. A machine with 85% RTP returns, on average, 85p for every £1 staked over the long run, and the rest is kept by the operator.

A worked example from Wikipedia: on a $1-per-spin game with 95% RTP, players who stake $1,000,000 over a million spins get back about $950,000. The operator keeps about $50,000. Individual players can win or lose far more than 5% in a session, but the operator’s share is built in.

RTP	Average kept by the operator per 100 staked
99%	1
95%	5
90%	10
85%	15

Minimum payback rules vary by place. Wikipedia lists, for example, a 75% legal minimum in Nevada and 90% in Western Australia, while the UK Gambling Commission says there is no minimum RTP on a gaming machine. Unlicensed online sites answer to no one on this.

What is volatility?

Volatility (or variance) describes how a game’s wins are spread out. Low-volatility games pay smaller wins more often. High-volatility games pay larger wins less often, which means longer losing runs. Volatility changes how a session feels, but it does not change the house edge.

Who checks that a slot is fair?

In a regulated market such as Great Britain, games that rely on RNGs must be tested by an approved test house before launch, and operators must monitor live games to confirm they deliver their designed RTP. Players using unlicensed sites have no regulator checking that the RTP shown is the RTP delivered.

Is online slots legal in Singapore, Malaysia or Thailand?

Singapore: Singapore Pools is the only operator licensed by the Gambling Regulatory Authority (GRA) for remote gambling. Playing slots with an unlicensed online operator while in Singapore can lead to a fine of up to S$10,000, up to 6 months’ jail, or both. See online casino Singapore: is it legal?

Malaysia: online gambling is prohibited under the Betting Act 1953 and the Common Gaming Houses Act 1953, and there is no online casino licensing system. See online casino Malaysia: is it legal?

Thailand: online gambling is illegal under the Gambling Act B.E. 2478 (1935). See online casino Thailand: is it legal?

Slots FAQ

Can you predict when a slot will pay out?

No. Each result is decided by the RNG, and past spins do not change the odds of the next one.

Does a higher RTP mean I will win?

No. RTP is a long-run average across all players. In any session you can lose your whole stake.

Are online slots legal in Malaysia?

No. Online gambling is prohibited under the Betting Act 1953 and the Common Gaming Houses Act 1953.

Getting help

If gambling is causing problems for you or someone close to you, call the National Problem Gambling Helpline (Singapore) on 1800 666 8668 (daily, 8am–11pm).

Related guides

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Sources

AuthoritySlot does not link to, promote or earn from any gambling operator. This page explains how a game works; it is not an invitation to gamble and not legal advice. Last checked: 24 October 2026.