Here's how much cash Warren Buffett carries in his wallet

Warren Buffett, who is worth nearly $89 billion according to Forbes, is famous for spending only $3 a day on breakfast.

So how much cash does the frugal billionaire have in his wallet?

"I probably carry maybe $400," Buffett told Yahoo Finance editor in chief Andy Serwer in an interview published Monday.

"My wife likes to use cash, so I just take home a chunk of cash every now and then and she doles it out," said Buffett of wife Astrid Menks. 

"She looks at my billfold and sees whether all the 100s are gone," Buffett said.

Buffett said he uses cash "98% of the time. If I'm in a restaurant, I'll always pay cash. It's just easier."

But he does have at least one credit card: "I've got an American Express card which I got in 1964," Buffett said. (Buffett's holding company, Berkshire Hathaway, owned 17.9% of American Express at the end of 2018, according to its year-end financial report.)

Buffett's tendency to use cash puts him in the minority among Americans — in 2018, only 18% made "all or almost all of their purchases" with cash, according to the PEW Research Center. About half (52%) of Americans made "some" of their purchases with cash and 29% made none of their purchases with cash.

Using cash, however, can actually be a good way to save money. Paying with cash can be used as a negotiation tool, according to Mark Cuban. And researchers have found that physically handing over money feels painful, making you less likely to do it, CNBC Make It previously reported.