The payout percentage is the ratio of the money a player wagers vs the money they win. So if a casino has a payout percentage of 98%, it means that if a player wagers $1 million, he will win $998,000 and the casino will keep the remaining $2,000. Of course, when players recirculate the same money, the edge of the house will grind down the bankroll; in the end, players will retain a lot less than 98% of the money wagered. The best way to calculate your payout percentage is to separate the money you bet vs the money you win.