House edge and RNG

House edge and RNG are the two ideas on which every casino game, slot machine and lottery is built. The house edge is the small share of all the money bet that the operator keeps over time. The "house" is the casino, or whoever runs the game. An RNG, or random number generator, is the program that decides each result by chance, so that neither the player nor the operator can predict it or change it.

Here is how the house edge works. Each game pays winners slightly less than their true chance of winning would justify. Take a roulette wheel with 37 numbered pockets, from 0 to 36. A bet on one number wins, on average, once in 37 spins. But a win pays only 35 times the stake, plus the stake back, as if there were 36 pockets. So, over many bets, the casino keeps about ₹1 of every ₹37 bet, which is about 2.7 per cent. Any one player may win or lose on a given night. Across lakhs of bets, the casino's share comes out very close to 2.7 per cent. On a slot machine, the same idea is described from the player's side, as the return to player, or RTP. A machine with an RTP of 94 per cent pays back ₹94 of every ₹100 played, over time, and the casino keeps ₹6.

Here is how the RNG works. Inside the game's computer, the RNG produces new numbers all the time, thousands every second, even when nobody is playing. At the moment a player presses the button, the game takes the current number and turns it into a result, such as the symbols on the reels. Nobody can time a press to the thousandth of a second, so nobody can predict the result. Before a game may be used, an independent testing laboratory checks that its RNG is truly unpredictable and that the game pays back what it claims. A regulator then certifies it.

Take, for example, a slot machine in a casino. Its RNG picks each spin, and its certified RTP fixes how much it pays back across a year of play.

Consider an online card game. In online casino games, an RNG on the operator's server shuffles the cards, and the same kind of certification applies.

Say a state government sells lottery tickets. Its lottery system pays out only part of the ticket money as prizes, and a certified machine or RNG makes the draw.

Even in social casino games, played only for virtual coins, an RNG decides each result.

How is the house edge different from the margin in in-play odds for sports betting? A casino game's edge is fixed by its rules and is the same on every bet. A bookmaker builds its margin into the odds it sets, and those odds change during a match as live data arrives. In both cases, players as a group lose over time, which is why regulators also require responsible gambling tools.