What is RNG in Online Casinos and How Does It Work?

Every time you spin a slot or play digital blackjack, the outcome is decided instantly by a Random Number Generator (RNG). RNGs are computer algorithms designed to ensure fairness by producing unpredictable results. But how do they really work, and can players trust them? This guide explains the basics of RNGs, why they matter, and how independent labs test them to keep games fair. For trusted casinos using certified RNGs, see our list of licensed online casinos.

How Does a Random Number Generator Work?

An RNG is a piece of software that produces random results millions of times per second. Most online casinos use pseudo-random number generators (PRNGs), which rely on a starting “seed number” and mathematical algorithms. The seed is updated constantly, so each spin, card, or dice roll is unpredictable.

For example, in a slot game the RNG assigns a number to every symbol on every reel. When you press spin, the RNG generates a set of numbers that match those symbols, creating the result. The same principle applies to roulette wheels (numbers 0–36) or blackjack decks (1–52 cards).

Why RNGs Make Casino Games Fair

Without RNGs, online games could be predictable or manipulated. RNGs ensure:

• Every spin or hand is independent of the last one.
• Players cannot predict outcomes.
• Casinos cannot change results based on bet size or winnings.

This means your odds are always based on the game’s built-in payout percentage (RTP), not external factors. RNGs are the digital equivalent of shuffling a deck or spinning a real roulette wheel. For mobile-focused players, our guide to mobile casinos explains how fairness is maintained on apps as well.

Which Casino Games Use RNG?

Most digital casino games rely on RNG software:

• Slots: RNGs assign values to reel symbols to create random results.
• Roulette: RNGs generate numbers that correspond to the wheel pockets.
• Blackjack and card games: RNGs simulate shuffled decks for each hand.
• Video poker: RNGs deal random cards from a virtual deck.

The only exception is live dealer games, which use real cards or wheels operated by a human dealer on camera.

When Does the RNG Decide the Result?

The outcome is fixed the moment you press play. For example, in slots the RNG result is determined the second you hit “spin,” not when the reels stop spinning on screen. The animations are only there to display the already-decided outcome.

Independent Testing of RNGs

Reputable casinos use independent labs to verify that their RNGs are fair and truly random. Leading auditors include:

• eCOGRA – Industry-recognized testing agency.
• Technical Systems Testing (TST) – Now part of GLI, specializing in RNG audits.
• iTech Labs – Global testing lab with strict certification standards.

These organizations run statistical tests, check payout percentages, and perform penetration/security checks. Certified casinos display their logos and certificates, giving players confidence that outcomes are not manipulated.

Common Questions About RNGs

Can casinos rig RNGs? Licensed casinos cannot. RNGs are tested regularly by third parties, and regulators require certification. Unlicensed or shady casinos may not offer the same guarantees.

Are RNG games truly random? Yes — within the limits of computer algorithms. For players, the difference between “true random” and PRNG is invisible. Every result is unpredictable and fair.

How do I know if an RNG is fair? Check for certification logos (eCOGRA, iTech Labs, GLI) and always play at regulated casinos.