President Trump’s massive tax-cut proposal would slash taxes on hundreds of businesses he and his family own.

The White House on Wednesday unveiled a proposal that would cut the top tax rate for corporations, as well as entities known as pass-through businesses, to 15 percent.

That could prove to be a windfall for the Trump Organization, the private umbrella company for hundreds of Trump real estate, licensing and other companies, many of which qualify as pass-through businesses.

Trump has refused to release his tax returns, making it impossible to know how much his businesses could save on taxes.

In addition, the White House said it would create rules to prevent wealthy individuals and corporations from taking advantage of the low pass-through rate. But because they did not provide details, it’s difficult to know how those rules would apply to the Trump companies.

“We will make sure that there are rules in place so that wealthy people can’t create pass-throughs and use that as a mechanism to avoid paying the tax rate that they should” pay on personal income, Treasury Secretary Steven Mnuchin said Wednesday.

A copy of Trump’s tax return from 2005 suggests that a tax cut similar to the one Trump is proposing could have lowered his tax obligation by potentially tens of millions of dollars in a single year.

“Trump is the king of pass-throughs,” said Steven M. Rosenthal, a senior fellow at the nonpartisan Tax Policy Center. “He has pass-through businesses everywhere. This is a very large issue.”

The Trump Organization, which itself qualifies as a pass-through business, did not respond to requests for comment.

The White House also did not respond to questions from The Washington Post about how Trump’s tax-cut proposal could affect his finances. In a news conference with reporters, Mnuchin declined to answer how the cuts could benefit the president or his businesses, saying, “What this is about is creating jobs and creating economic growth.”

Asked whether the president would release his tax returns, Mnuchin said that Trump “has no intention” to release and “has given more financial disclosure than anybody else.”

[White House unveils dramatic plan to overhaul tax code in major test for Trump]

(Jhaan Elker/The Washington Post)

Trump could stand to benefit personally from one of the proposal’s broadest changes, which would drop the income-tax rate for America’s wealthiest individuals from 39.6 percent to 35 percent.

Trump also called for a repeal of the “alternative minimum tax,” a parallel tax system that kicks in when taxpayers request many itemized deductions and that rejects specific deductions, including for assorted real estate write-downs that Trump tapped in past years. That tax collectively raised Trump’s 2005 income taxes and self-employment taxes from $7 million to $38 million, according to a copy of Trump’s 2005 return released last month.

The proposed pass-through rate cut could make a big impact on the Trump company’s bottom line. Pass-through businesses do not pay corporate taxes; instead, that income passes through to the owner’s personal income taxes, skipping the corporate-tax rate altogether.

That income is then taxed at the owner’s income-tax rate, which now is capped at 39.6 percent. Trump’s proposed drop would essentially cut pass-through business owners’ top tax rate from 39.6 percent to 15 percent.

That drop would also cost government budgets an estimated $1.5 trillion over the next decade, according to the Tax Policy Center. About 40 percent of that lost money would come from people reclassifying their income or incorporating as a pass-through business so they could pay taxes at a lower rate, the center said.

[Treasury secretary says Trump ‘has no intention’ of releasing tax returns]

One clue to how much Trump’s private company could save from this cut comes from his 2005 tax return. The return shows that Trump filed for $42 million in business income and $67 million in income from partnerships, S-corporations, trusts and other entities. The proposed pass-through tax cut could have lowered Trump’s tax obligation by tens of millions of dollars in that year alone.

Trump left the management of his private companies to his adult sons and a longtime employee. He also shifted his assets into a revocable trust, moves that Trump and his lawyers said would resolve worries over conflicts of interest. But Trump can draw money from the trust whenever he wants and can dissolve it at any time, filings show.

The pass-through rate cut proposal could also benefit Jared Kushner, Trump’s son-in-law and a White House senior adviser. In financial disclosure forms, Kushner reported owning a stake in nearly 300 different assets or companies collectively worth hundreds of millions of dollars, most of which he still owns. Hundreds of those companies classify as pass-through businesses.

Most American businesses are pass-throughs, including limited-liability companies (LLCs), S-corporations, partnerships and sole proprietorships. The Tax Foundation, a nonpartisan think tank, estimates that pass-throughs account for more than 90 percent of all companies in the United States.

Although pass-throughs were designed for small businesses, many law firms, real estate partnerships, hedge funds and other big companies are now counted among their ranks, often in pursuit of tax savings and other benefits. Shareholders of traditional companies, known as C-corporations, pay taxes on not just corporate income, but on any gains tied to selling stock or receiving dividends.

Small businesses and their lobbying groups have championed pass-through tax cuts by saying they would encourage new investments and increased hiring. During his presidential campaign, Trump referred to pass-through cuts as an important boost to America’s small businesses and self-employed entrepreneurs.

But a large part of the pass-through tax savings is enjoyed by America’s richest taxpayers. A 2015 study by the nonpartisan National Bureau of Economic Research said that 69 percent of pass-through income earned by individuals goes to the top 1 percent of tax filers.