Hillary Clinton's proposed tax would affect roughly 0.02 percent of taxpayers. | AP Photo Clinton proposes a new 4 percent tax on the wealthy

Hillary Clinton today proposed a 4 percent surtax on the highest-earning Americans, as she seeks to boost taxes for the wealthiest Americans.

The proposal, which she announced in Iowa, would raise an estimated $150 billion over a decade, a Clinton aide said, and comes after the Democratic front-runner said that she would build on the so-called Buffett Rule that seeks to ensure that the middle class doesn't pay a higher tax rate than top earners.


The surtax would hit those with annual income of more than $5 million, and would affect roughly 0.02 percent of taxpayers.

Clinton is calling the plan a “fair share surcharge.” The Clinton aide cast the approach as a simple way to raise effective tax rates on the wealthiest, who can rely on tax planning and find ways to game the tax system.

The IRS recently announced that the 400 highest earners paid an average rate of less than 23 percent in 2013. They paid less than 17 percent in 2012, before the fiscal cliff deal raised taxes on the wealthy.

Clinton has said she will solely use tax hikes on the wealthy to pay for a variety of domestic initiatives, including expanded paid family leave. Her main rival, Sen. Bernie Sanders of Vermont, has called for a slight but broad increase in the payroll tax to boost family leave.

Clinton’s camp says she will roll out more proposals this week to force the wealthy to pay more in taxes.