He argued that taxing too much, though, could jeopardize the U.S.' status as the place to build innovative businesses. Gates said he was somewhere in between the extremes of cutting the estate tax and imposing a 6% wealth tax on billionaires, an idea Warren, a Massachusetts senator, floated last week . Gates said the estate tax could be higher.

"I'm all for super-progressive tax systems," said Gates , the world's second-richest person and co-chair of the nonprofit Bill & Melinda Gates Foundation, during an appearance at the New York Times' DealBook conference in New York on Wednesday.

Democratic presidential candidate Elizabeth Warren announced on Wednesday that she would be willing to meet with Bill Gates, hours after the Microsoft co-founder stopped short of expressing support for Warren's proposed 6% tax on billionaires to cover Medicare costs. He had said he wasn't sure if she would be open to sitting down with him.

Warren's willingness to talk with Gates suggests that there could be even more attention on an already controversial policy that's emerged in the run-up to the 2020 presidential race. In recent days Warren has exchanged criticisms with investor Leon Cooperman in the context of the federal contributions billionaires ought to make.

Gates said he has paid over $10 billion in taxes, more than anyone else, and would be happy to pay $20 billion.

"When you say I should pay $100 billion, OK, then I'm starting to do a little bit of math about what I have left over," Gates told Andrew Ross Sorkin, a New York Times columnist and co-anchor of CNBC's "Squawk Box." "Sorry, I'm just kidding."

Warren alluded to Gates' $100 billion comment in a Wednesday tweet in which she offered to meet with him.

@ewarren: I'm always happy to meet with people, even if we have different views. @BillGates, if we get the chance, I'd love to explain exactly how much you'd pay under my wealth tax. (I promise it's not $100 billion.)

Gates was asked how he would proceed if Warren were selected to face President Donald Trump in the election next year.

"I'm not going to make political declarations," Gates said. "But I do think no matter what policy somebody has in mind, a professional approach is even — as much as I disagree with some of the policy things that are out there, I do think a professional approach to the office — whoever I decide would have the more professional approach in the current situation probably will weigh — is the thing that I'll weigh the most."

Gates is hoping the more professional candidate is electable, he added.

"I'd love somebody to find a middle-ground approach, because the government's role in health care and better education — the government does need more resources than it has today," Gates said.

WATCH: Sen. Warren has a new tax proposal