The "Shark Tank" star has eight credit cards, but says you should have at least two.
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Many financial experts agree that utilizing credit cards in a responsible way is an important route to building credit, so that you can then borrow money at a decent rate for big purchases like a home or car.
Even Kevin O'Leary, star of ABC's "Shark Tank" and a financial expert, who strongly advocates against taking on unnecessary debt, recommends swiping a credit card every now and then.
And he has a strategy.
"I recommend that everybody have at least two credit cards," O'Leary tells CNBC Make It.
"The first credit card is one that has a very low limit, let's say $2,000," O'Leary explains. "That's the [one] you use on all the online services. If they get hacked, nobody can spend more than $2,000. That's how you protect yourself.
"The other card is the one you use when you actually buy things that are not online," he adds. "And perhaps, those purchases can be much more expensive. But you haven't exposed that number to the Internet. You need both. One that's out there, and one that's private. That's the way to do it."
As for credit card rewards programs — getting points for purchases, which can be redeemed for a wide array of goods — skip rewards like airline miles and gift cards and go for a cash-back option, he recommends.
"Forget about affinity points," O'Leary says. "There's so much inflation in that. You get less and less every year for the points. Get the cash back."
So how many credit cards does O'Leary himself have?
O'Leary travels frequently, often internationally, for business and pleasure, so he carries eight different credit cards in multiple currencies, like Swiss francs, British pounds, euros and more.
"I look for efficiency, and having all these credit cards gives me diversity. It makes sure that I'm not being charged for currency conversion. Drives me out of my mind when I'm buying something in London and I'm getting whacked on a conversion price back in U.S. dollars. That doesn't happen to me, because I have one in British pounds," he says.
"My whole thing about credit cards is I don't like fees," O'Leary says. "I'm cheap."
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Kevin O'Leary: This is how many credit cards you should have (and how to use them) | CNBC Make It.