Mortgage Interest Deduction

The mortgage interest deduction is a federal income tax allowance that permits taxpayers who itemize deductions to subtract the interest paid on up to $750,000 of qualifying home debt, reducing taxable income and thus tax liability.

Scope and eligibility

Only taxpayers who itemize deductions can claim the benefit. The standard deduction—a flat reduction in taxable income available to all—has risen substantially since the Tax Cuts and Jobs Act of 2017, making itemization uneconomical for many filers. In recent years, the standard deduction exceeds $13,000 for single filers and $26,000 for married couples. Unless a homeowner’s total itemized deductions (mortgage interest, property taxes, charitable giving, and state income taxes) exceed these thresholds, the standard deduction yields a larger benefit.

The mortgage interest deduction applies to qualified residences, defined as the taxpayer’s primary home and one secondary home (such as a vacation property). Debt on investment properties, rental houses, or personal real estate other than these two does not qualify. The interest must be on debt used to buy, construct, or substantially improve the residence; interest on a loan taken out against home equity but used for consumption (a vacation or car purchase) does not qualify.

The $750,000 acquisition debt cap

Prior to 2018, the cap on acquisition debt was $1,000,000. The Tax Cuts and Jobs Act reduced it to $750,000 for loans taken after December 31, 2017. For mortgages executed before 2018, the $1,000,000 limit still applies, creating a stair-step in deductibility across vintages.

Acquisition debt is the debt used to acquire, construct, or substantially improve the home. Home equity lines of credit (HELOCs) and loans secured by the home but used for other purposes fall into a secondary category: home equity debt, which carries its own $100,000 cap (or $50,000 for married individuals filing separately). Interest on home equity debt was temporarily non-deductible from 2018 to 2025 but has been restored.

A homeowner with a $600,000 mortgage and a $200,000 HELOC used for living expenses can deduct interest on the full $600,000 mortgage (within the $750,000 limit) plus interest on only $100,000 of the HELOC, even though the HELOC balance is $200,000.

Deductibility in practice

The deduction value depends on marginal tax bracket. A high-income earner in the 35% bracket who pays $15,000 in mortgage interest will save $5,250 in federal tax. A middle-income earner in the 22% bracket paying the same interest saves $3,300. Low-income earners in the 10% or 12% brackets save correspondingly less, and those below the standard deduction threshold save nothing at all.

This creates a regressive outcome: wealthy homeowners—who carry larger mortgages and itemize—receive larger tax benefits, while middle-income and lower-income homeowners derive less value or none. In effect, the federal government subsidizes borrowing disproportionately for the wealthy.

Historical context and policy debate

The mortgage interest deduction is one of the oldest and most generous tax preferences in the federal code, dating to the income tax’s inception in 1913. Its original purpose was to avoid taxing the implicit rent homeowners derive from living in their own homes; if the home generates no cash income, the logic went, its financing costs should not be deductible. Over a century, the rationale has eroded, and the deduction now functions as a blanket subsidy to real estate investment.

Economists and tax policy experts debate whether the deduction makes homes more affordable. Critics argue it inflates housing demand and prices, especially in high-tax states where combined mortgage interest and property tax deductions are substantial. Removing it would lower effective ownership costs for wealthy buyers but could reduce home prices, offsetting some losses. Proponents counter that the deduction encourages homeownership and wealth-building through home equity, supports construction employment, and that eliminating it would represent a large tax increase on an already-overburdened class.

State and local tax (SALT) deduction interaction

The deduction interacts with the state and local tax (SALT) deduction, which caps total deductions for income and property taxes at $10,000 per year. Homeowners in high-tax states like New York and California face binding SALT caps, which limit total itemized deductions. In such cases, mortgage interest and property taxes compete for the same ceiling, reducing the real benefit of mortgage interest deduction in high-tax jurisdictions.

Refinancing and prepayment

When a homeowner refinances a mortgage, the new debt replaces the old. If the new loan is for a larger amount than the original (a cash-out refinance), only the portion used to pay off the original debt qualifies as acquisition debt; the incremental amount is home equity debt, subject to the $100,000 cap. This discourages using refinances to extract home equity for non-home purposes, though the distinction is technically porous.

Mortgage prepayment does not affect deductibility. A homeowner can pay down a $750,000 mortgage to $500,000 and claim interest deductions on the outstanding balance. Conversely, taking out a new HELOC against the paid-down equity does not restore acquisition debt status.

Sunset and future uncertainty

The Tax Cuts and Jobs Act provisions, including the $750,000 cap, are scheduled to expire at the end of 2025, reverting to $1,000,000. The future trajectory is uncertain and depends on legislative action. If the cap reverts, many homeowners’ deductions will increase. If Congress extends the $750,000 cap, the status quo persists.

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