If they're no longer easy to shuffle or stick together, it's probably best to get a fresh deck. And of course, if you're missing any cards, you should definitely buy a new pack. "Basically when they get too dirty to use, you have to change them out," says Kalush. This could include the edges getting too dark or spotting on the cards that make it hard to see the number or suit. Routinely freshening up your cards can help them last long, says Kilbert. "Plastic cards should last for years as long as you refresh them periodically by dropping them a a solution of dishwashing liquid and drying them thoroughly," he says. He also recommends owning two decks to switch between.