Washington (CNN) Sen. Elizabeth Warren is promoting an online calculator that shows voters just how much -- exactly -- they'd benefit from her proposal to cancel outstanding student loans.

Speaking Friday at Iowa State University, the Massachusetts Democrat and 2020 presidential hopeful asked people to take out their phones and plug their debt amounts into the calculator , which is available on her campaign's website.

"Anybody in here have student loan debt? Anybody in here know someone with student loan debt? Okay, I think we got almost everybody," the Massachusetts Democrat said.

The calculator, she added, is "a way to make real to people what it means to talk about student loan debt cancellation."

Warren released her loan forgiveness plan last week, which she says would be paid for by her proposed wealth tax . Her campaign estimates that the one-time debt cancellation would cost $640 billion.

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