Are progressive jackpots random: the short version

Penny slots work on the smallest coin value a machine accepts, but almost no one plays a single penny. Each spin multiplies that value by the number of lines and by a bet level, so a penny slot with fifty lines costs fifty times its coin value or more on every spin. That is why penny slots are so expensive in practice: the headline value is small while the real stake, and the speed of play, add up quickly. How much a session costs follows from that per spin figure.

Progressive jackpots work by taking a small share of every stake and adding it to a prize that keeps growing until someone wins it. The jackpot meter on the screen shows that running total, and on networked games it rises with stakes from many casinos at once. A mystery progressive jackpot is paid at a random moment before the meter reaches a hidden limit rather than on a symbol combination, so any spin can trigger it.