Sen. Elizabeth Warren rolled out a “calculator for the billionaires” on Thursday in a not-so-subtle swipe at her superrich critics Bill Gates and Leon Cooperman, both of whom recently attacked her wealth tax.

“Some billionaires seem confused about how much they would pay under my #TwoCentWealthTax,” the Warren campaign said, referring to her signature tax. “Don’t worry, now we have a calculator for that too.”

Users are invited to identify their net worths, as well as whether they are billionaires. Special links are included for Gates and Cooperman that autofill their estimated fortunes – $107 billion and $3.2 billion, respectively.

The calculator comes a day after Gates criticized Warren's wealth tax, which would impose a 2% tax on households with net worths above $50 million and levy a 6% rate on fortunes over $1 billion annually. The tax forms a key part of her populist campaign, and Warren has welcomed public clashes with billionaires to highlight her progressive zeal.

At the New York Times Dealbook Conference on Wednesday, Gates said he already paid $10 billion in taxes and he would be "fine" with paying $20 billion.

"But, you know, when you say I should pay $100 billion, OK, then I'm starting to do a little math about what I have left over," Gates said. "Sorry, I'm just kidding. So you really want the incentive system to be there, and you can go a long ways without threatening that."

Gates then said he hadn't spoken with Warren and questioned her willingness to meet with a wealthy person. He could pay over $6 billion in wealth taxes under Warren's proposal.

"You know, I'm not sure how open-minded she is, or that she'd even be willing to sit down with somebody, you know, who has large amounts of money," Gates said.

Warren responded later in the evening with a tweet saying: "I'm always happy to meet with people, even if we have different views. @Bill Gates, 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.)"

Cooperman is another critic of the Massachusetts senator, and he has slammed her wealthy proposals as needlessly vicious to American billionaires.

"I don't need Elizabeth Warren telling me that I'm a deadbeat and that billionaires are deadbeats," Cooperman told CNBC on Monday. "The vilification of billionaires makes no sense to me."

The hedge-fund manager later said: "This is idiocy. It's appealing to the lowest common denominator and basically trying to turn people's heads around by promising a lot of free stuff."