Elizabeth Warren’s campaign just rolled out a handy wealth tax calculator for any billionaires worried about what they’d have to pay under her proposed tax plan.

The Massachusetts senator, who’s polling neck-and-neck with Bernie Sanders and Joe Biden for the 2020 Democratic presidential nomination, said she’d double her proposed wealth tax on billionaires from 3% to 6% to fund her progressive health care, climate, child care, and student loan proposals. Under the plan, billionaires would be taxed 6 cents for every dollar over $1 billion they’re worth. The plan would also put a 2% tax on net worth between $50 million and $1 billion.

Unsurprisingly, some billionaires aren’t too happy about it — and now Warren’s campaign has calculated just how much they stand to lose if she becomes president and enacts the tax.

According to the calculator, Facebook CEO Mark Zuckerberg would pay $4.249 billion. Amazon founder and CEO Jeff Bezos, who happens to be the richest man in the world, would pay $6.697 billion. And Bill Gates, who declined to say whether he’d vote for Warren earlier this week, would pay $6.379 billion if her plan goes into effect.

“Don’t worry too much about Bill Gates — if history is any guide, if billionaires do nothing other than invest their wealth in the stock market, it’s likely that their wealth will continue to grow,” Warren’s website reads.

Gates does seem a little worried, though.

“I’m all for super-progressive tax systems,” Gates said at a Wednesday conference. “I’ve paid over $10 billion in taxes. I’ve paid more than anyone in taxes. If I had to pay $20 billion, it’s fine.”

But he doesn’t seem to be fine with Warren’s tax plan, even though he’d pay less than $10 billion or $20 billion each year.

“But when you say I should pay $100 billion, then I’m starting to do a little math about what I have left over,” he continued. “So you really want the incentive system to be there, and you can go a long way without threatening that.”