Casino games make money for the house by paying less than the true odds of winning the bet. At double zero roulette, for example with numbers 1 through 36 plus 0 and 00, the true Roulette odds against any specific number are 37-1, but the house pays single-number winners only 35-1.
Slot machine odds work in a similar fashion to the roulette example, except there are many more possibilities on the slots.
There are thousands, and sometimes millions, of reel combinations.
There also is an open field for game designers to assign how much each winning combination pays.
The number of winning combinations and the payoffs per winner work together to determine a game’s odds.
The sheer number of possibilities makes the math that goes into slot machine odds more complicated than on table games.
The change to virtual reels enabled programmers to make the reels to behave as if they had any number of stops.
With 100 stops on each of three reels, there are 1 million combinations.
The Megabucks three-reel slot that paid the world record jackpot of more than $39 million has about 50 million combinations.
Most modern video slots have five video reels can be as long as the gamemaker needs them to be.
With 100 symbols on each of five reels, there are 10 billion combinations.
To see how slots pay less than true odds to give the house an edge, let’s set up an example that’s as streamlined as slot odds can get, a game of the type used in the early decades after Charles Fey invented the three-reel slot machine in 1895.