"He will have a tax increase," Mnuchin said. "For people who make over $1 million in the high tax states, there will be a tax increase."
Mnuchin was speaking at The Economic Club of New York ahead of the unveiling of the Senate GOP tax plan expected later Thursday.
Initial analyses of the tax plan suggest that Trump will see his federal tax rate decline if the Republican tax proposal is passed. His total tax rate, however, including state and local taxes, could increase, just as Mnuchin said.
Trump, like others making $1 million a year in taxable income, will benefit from a reduced federal tax rate, according to an analysis by the Joint Committee on Taxation. That analysis showed that the average millionaire will go from a tax rate of 32.5 percent to 29.9 percent.
The numbers could change as the House is revising the bill in committee.
Despite the likely decrease in his federal tax rate, taxpayers such as Trump who live in high-tax states and localities will be hit hardest by the House GOP's proposed end to state and local deductions for itemized filers.
The state and local tax deduction, or SALT deduction, is effectively a subsidy from the federal government to state and local governments. It's generally used by higher-income taxpayers and is disproportionately used by taxpayers in states with high state and local taxes. In Washington, D.C., the average SALT deduction in 2014 was $15,500, according to the Tax Policy Center.
For his part, Trump said Tuesday that he called his personal accountant to check how he would be affected, according to The Washington Post. According to the Post, the president told senators Tuesday that he would be a "big loser" under the plan.