WASHINGTON — All it took for Debbie Hays to make the jump from long-time renter to first-time homeowner was a bit of math.

The 58-year-old looked at the increasing rent checks she was signing for her Plano apartment of 15 years. She then eyed the prospect of paying about the same for a $1,100-a-month mortgage to own a cheery Cape Cod-style bungalow in Denton County’s Providence Village.

And one key part of her calculation was the mortgage interest deduction she now takes each year on her tax returns.

“It puts an incredible amount of money back in my savings account,” said Hays, who made the move in 2014.

That perk that so many tout as critical to boosting homeownership could be threatened as Congress pursues what would be the first major overhaul of the tax code in three decades.

The break — which allows individuals who itemize their tax returns to deduct the interest paid on mortgages of up to $1 million — isn’t likely to disappear. But the incentive could be capped at a much lower threshold or otherwise lessened through other efforts to streamline the tax code.

The potential impact, however, is hard to define.

Most taxpayers in Texas and everywhere else don't use the mortgage interest deduction. Those who do tend to be wealthier. And there's a chance that the negative side effects from tweaking the break could be offset by lower tax rates and other perks that lawmakers are pursuing.

“For the average taxpayer, it’s a big ‘so what?’ ” said James Gaines, chief economist at Texas A&M University’s Real Estate Center.

The mortgage interest deduction, by all accounts, is a political powerhouse. But what’s been described as an “American birthright” has also been dubbed the “accidental deduction.”

The break, which dates back a century, was initially folded into a broader provision covering “all interest paid within the year by a taxable person on indebtedness.” And since so few Americans paid federal income tax at that time, the perk’s original purpose is a bit muddied.

"One thing is clear: Congress did not see it as a way of promoting homeownership," Dennis Ventry, a University of California-Davis professor, wrote in a 2016 study of the break's history.

House Ways and Means Committee Chairman Kevin Brady, R-Texas, center, has pledged to "continue to reward homeownership." (J. Scott Applewhite / The Associated Press)

But that vision has evolved over the years.

More than 75 percent of homeowners use the deduction at some point while owning a home, according to the National Association of Realtors. Politicians are loathe to speak ill of the perk, in part because it’s become so closely tied to the classic vision of the American dream.

And for those who take the break, it means real savings that average $1,950 a year, according to the Urban-Brookings Tax Policy Center.

“The home is the largest, single asset that most families buy,” said Kent Conine, a past president of the Dallas Builders Association. “We want to incentivize that however we can.”

Debbie Hays bought her first home in Providence Village three years ago, and just this month won her neighborhood's "Yard of the Month" award. She counts on the mortgage interest deduction as a major source of savings. (Courtesy of Debbie Hays)

Consider Hays, who takes the break on her Providence Village home. She described the purchase as a transformative event, proudly noting that she recently won “Yard of the Month” for an immaculately landscaped array of flowers and bushes.

“I never thought this would have been possible,” she said.

That viewpoint is echoed by 53-year-old Laura Harshbarger.

She and her husband purchased a two-bedroom home in North Richland Hills after also seeing their rent go up every year. The tax implications were among the factors they considered in the process as they looked for a home with a good commute and space for their dogs.

“It’s one of the few breaks we get,” said Harshbarger, who works for an insurance company in Dallas.

But the mortgage interest deduction has its skeptics.

Only one in five taxpayers use the break, opting instead for the standard deduction. Gaines, the Texas A&M expert, said he sees the perk used more as “gravy” for homebuyers, with other factors playing a much bigger role in who buys a home and how they pick the right one.

And critics point out that the wealthy are much more likely to benefit.

About 60 percent of those who take the break have an annual income of $100,000 or more, and that group accounts for about 80 percent of the benefits produced by the deduction, according to Congress’ Joint Committee on Taxation.

“Where do we as a nation want to spend money on housing?” said Sarah Mickelson of the National Low Income Housing Coalition. “It should go to the people with the greatest need.”

The perk also presents Congress with a financial crunch.

Top GOP policymakers want to overhaul the tax code by lowering rates, increasing the standard deduction and ending provisions like the estate tax. That costs a lot of money. And measures like the mortgage interest deduction represent billions of dollars that could be used as offsets.

So while the break is likely to remain on the books, one rumored proposal would cap the deduction to interest paid on home mortgages of up to $500,000.

That wouldn't shrink who can use the perk. The Urban-Brookings Tax Policy Center estimates the change would reduce the average benefit for users by $130 per year, with the wealthy bearing the brunt. And the Tax Foundation, a conservative-leaning think tank, says it would raise $300 billion over the next decade.

President Donald Trump has been prodding Congress to overhaul the tax code. (Alex Brandon / The Associated Press)

But that's a non-starter for the housing industry, even though only 7 percent of Texas homes were last year priced at half a million dollars or more, according to Texas A&M Real Estate Center.

The deduction's backers argue that even a cap would hurt homeowners, particularly since the limit has been static for 30 years. They also say it could be part of a double-whammy, since ideas like axing the state and local deduction would ding those with lots of local property taxes.

And one of the big worries is that such changes could lower home prices, causing some in Texas and across the U.S. to go underwater on their mortgages.

“The impact would be greater than is realized in the numbers,” said James Martin, a Dallas real estate agent who serves as president of the MetroTexas Association of Realtors.

But some are skeptical of those predictions. Homeowners, such as Harshbarger in North Richland Hills, say they might be willing to make a trade for something like a doubled standard deduction, even if that would effectively reduce the incentive of the mortgage perk.

And some top lawmakers have sought to reassure homeowners.

“We will continue to reward homeownership,” Texas Rep. Kevin Brady, the House’s top tax writer, said last month. “And we are exploring ways ... where we can reward and encourage more ownership.”