Republican leaders recently offered reassurances that when Congress tackles taxes this fall, the mortgage interest deduction will be protected.
This begs the question: Who really benefits from it?
The vast majority of people see no tax benefit from the deduction, because just 20 percent of filers use it, according to the Urban-Brookings Tax Policy Center. And if Republicans successfully deliver generous increases in the standard deduction while eliminating other deductions, its utility could decline even more.
"At that point, very few people would claim the mortgage interest deduction," said Joseph Rosenberg, a senior research associate at the Tax Policy Center. "It may be the case that a lot of taxpayers wouldn't care if it went away, but it's a politically difficult thing to touch."
In an analysis of the GOP tax plan released last year, the Tax Policy Center estimated that of the 45 million filers who itemize, 38 million, or 84 percent, would opt for the $24,000 standard deduction proposed under the Republican plan because it would exceed the combined value of other deductions available to them.
The tax break for mortgage interest has remained unchanged since the Tax Reform Act of 1986, when it survived the legislative ax to deductions for other forms of consumer interest (such as on credit card debt). The provision generally lets taxpayers deduct the interest on mortgage debt up to $1 million, along with interest on home-equity debt up to $100,000.
To claim it, you must itemize deductions on your tax return, which only about a third of taxpayers do. Of those one-third, 74 percent take the mortgage interest deduction, according to the Tax Policy Center.
The biggest benefits tend to go to higher-income taxpayers. The 7.18 million filers with incomes of $200,000 or more who claim the deduction will reduce their taxable income by an aggregate $29.78 billion this year, according to recent tax expenditure estimates released by the congressional Joint Committee on Taxation.
In comparison, the 14.6 million filers with incomes of $100,000 to $200,000 will save less: $24.85 billion. Filers with incomes below that have even smaller tax savings.
Another group of taxpayers who find the deduction appealing are those in high-cost housing areas such as New York or San Francisco.
Often, taxpayers in high-cost ZIP codes also claim other deductions, including those for property taxes and state and local income taxes. It's unclear whether those deductions and others will remain as legislators identify ways to offset promised tax cuts with new sources of tax revenue.
The deduction for mortgage interest is among the most expensive individual tax breaks, costing an estimated $357 billion in revenue from 2016 through 2020, according to Joint Taxation Committee's recent report.
President Donald Trump's one-page tax plan released in April and the 35-page GOP tax reform blueprint released last year included elimination of all deductions except those related to charitable contributions and mortgage interest.
Since then, however, rumors have swirled on Capitol Hill that while the deduction might not go away, the cap on interest could be lowered to mortgage debt of $500,000, which would echo a provision in a Republican draft bill in 2014.
Supporters of the deduction include the National Association of Realtors, which says any changes would harm homeowners whether they have a mortgage or not.
The group released a study in May showing that if elements similar to GOP's plan went into effect, home values would fall by more than 10.2 percent on average in the near term.
The study also found that homeowners with income of $50,000 to $200,000 would face an average tax increase of $815 while non-homeowners in that range would get an average tax cut of $516.
Kathryn Hauer, a certified financial planner with Wilson David Investment Advisors in Aiken, South Carolina, said it's not just wealthy homeowners who like the mortgage interest deduction. She sees plenty of middle-class households where two earners bring in a combined $80,000 or so annually and rely on the break every year.
"For many homeowners, taking a deduction for that mortgage interest cost, which can be thousands of dollars, really helps lower their tax burden," Hauer said.