Mortgage Interest Deduction
Mortgage Interest Deduction
Mortgage interest is a direct deduction from rental real-estate income and can offset other income through passive loss rules. For primary-residence owners, the deduction is capped, but the tax savings are still substantial. The interaction between mortgage interest, depreciation, and property taxes creates powerful after-tax returns.
Key takeaways
- Mortgage interest on rental property is 100% deductible against rental income and can shelter other income (subject to passive-loss limitations).
- Mortgage interest on primary residence is deductible only if total acquisition debt is under $750,000 (under $1 million pre-2017 Tax Cuts and Jobs Act).
- State and local property taxes (SALT) are capped at $10,000 combined with income taxes, limiting the total tax-deduction benefit.
- A $1 million rental property financed at 70% loan-to-value (LTV) with 6% interest generates $42,000 annual mortgage-interest deductions.
- The deduction is greatest in year one (highest interest portion) and decreases over time as principal paydown accelerates.
Rental property: unlimited deduction subject to passive-loss rules
If you own a rental property and finance it with a mortgage, the full amount of mortgage interest is deductible against rental income. There is no cap on the size of the mortgage. A $10 million commercial building financed at 70% LTV ($7 million mortgage) at 5% interest generates $350,000 annual mortgage-interest deductions.
The key constraint is passive-loss rules. Rental real estate is generally classified as a passive activity. Losses from passive activities (including mortgage-interest deductions that exceed rental income) can be used to offset passive income only, not active income (wages, self-employment income) or portfolio income (dividends, capital gains).
However, real-estate professionals and active real-estate investors may be exempt from passive-loss limitations if they meet IRS tests. Additionally, up to $25,000 of rental losses can be deducted against active income by taxpayers with modified adjusted gross income under $100,000 (phasing out to $150,000).
In practice, most rental properties generate sufficient income to use mortgage-interest deductions directly. It's when you have multiple properties, depreciation losses, or capital-improvement deductions that passive-loss rules become binding.
Primary residence: the $750,000 cap
The Tax Cuts and Jobs Act of 2017 capped the mortgage-interest deduction on primary residences at interest paid on up to $750,000 of acquisition debt (down from $1 million). This applies to mortgages taken out after December 15, 2017.
The cap applies to acquisition debt only—debt incurred to purchase, construct, or substantially improve the home. Home-equity lines of credit (HELOCs) and other debt secured by the home but not used to acquire it are treated separately and are not deductible.
For a $2 million home in a high-tax state financed at 80% LTV ($1.6 million mortgage) at 6% interest:
- Mortgage interest: $96,000 annually.
- Deductible interest (on first $750,000 debt): $45,000.
- Non-deductible interest (on remaining $850,000): $51,000.
This cap has reduced the attractiveness of primary-residence ownership in high-cost real-estate markets. Combined with the $10,000 SALT cap (below), many high-income homeowners in expensive states have seen their total real-estate tax benefits shrink significantly.
The SALT cap and its interaction with mortgage interest
The Tax Cuts and Jobs Act also capped the combined deduction for state and local taxes (SALT)—including property taxes, income taxes, and sales taxes—at $10,000 per year. This cap is set to expire at the end of 2025 unless Congress extends it.
For a high-income earner in California, Massachusetts, or New York, the interaction is severe:
- Federal income tax: ~$200,000 (at 37% rate on high income).
- State income tax: ~$10,000 (if any, but California rate is 13.3%).
- Property tax on $2 million home: ~$20,000 (varies by locality).
- Total SALT: $30,000+.
The SALT cap means only $10,000 is deductible. The remaining $20,000 is lost forever. Meanwhile, mortgage interest of $96,000 is deductible (up to $45,000 on acquisition debt under the $750K cap).
Combined real-estate tax benefit: $45,000 + $10,000 = $55,000, on a $2 million property. This is meager—about 2.75% of home value in annual deductions.
By contrast, rental property in the same state incurs no SALT cap (deduction applies to business entity), and mortgage interest is unlimited. This explains why high-income investors in high-tax states often prefer to own investment property rather than maximize primary residence.
Amortization schedules and the interest/principal split
Early in a mortgage, payments are heavily weighted toward interest. Late in the mortgage, toward principal. This changes the tax benefit over time.
A 30-year $1 million mortgage at 6% interest:
- Monthly payment: $5,996.
- Year 1 total interest: $59,784 (deductible).
- Year 1 total principal: $11,952 (not deductible).
- Year 15 total interest: $34,316.
- Year 15 total principal: $37,420.
- Year 29 total interest: $3,548.
- Year 29 total principal: $68,188.
For investors seeking to maximize tax deductions in early years, this aligns well with cost segregation and bonus depreciation, which also front-load deductions. A property purchased in year one generates significant deductions from mortgage interest, depreciation, and cost-segregation components. By year 15, depreciation is unchanged, but mortgage interest has halved.
This creates a planning decision: should you refinance (reset the amortization schedule to boost interest deductions) or accelerate payoff? For tax purposes, carrying debt longer and maximizing interest deductions is advantageous if you're in a high tax bracket.
Rental income exceeding mortgage interest: a paradox
Some rental properties generate income that exceeds operating expenses plus mortgage interest. In this case, you have taxable rental income despite owning a property with cash flow. This is common in high-price-per-square-foot markets or fully-leveraged properties with modest debt.
Example: A rental apartment generating $60,000 annual rental income, with $15,000 in operating expenses and $30,000 in mortgage interest. Pre-tax cash flow: $60,000 – $15,000 – $30,000 = $15,000. But with a depreciation deduction of $18,000 (building value $500K, allocated at 70% structure ÷ 27.5 years), taxable income becomes negative: $15,000 (cash shortfall after deductions) + $3,000 (depreciation benefit) = $0 taxable income.
Wait—let me recalculate. Taxable income: rental income minus expenses minus mortgage interest minus depreciation = $60,000 – $15,000 – $30,000 – $18,000 = –$3,000. This is a paper loss, sheltering $3,000 of other income.
Meanwhile, actual cash received: $60,000 – $15,000 – $30,000 = $15,000. You have positive cash flow and a tax loss—the magic of depreciation. This is the reason real estate is favored: cash flow plus tax deferral.
Debt-equity ratio and leverage amplification
Higher leverage (more debt relative to equity) amplifies the tax benefit of mortgage interest:
Conservative leverage (50% LTV): $1 million property, $500K mortgage at 6% = $30,000 annual interest.
Moderate leverage (70% LTV): $1 million property, $700K mortgage at 6% = $42,000 annual interest.
Aggressive leverage (80% LTV): $1 million property, $800K mortgage at 6% = $48,000 annual interest.
At a 40% combined tax rate, the deduction benefit ranges from $12,000 to $19,200 annually. Over 10 years, that's $120,000 to $192,000 in tax savings—a difference that compounds.
Leverage increases risk (if rental income falls, debt obligations remain), but for tax-focused investors with stable income, higher leverage amplifies deductions.
Interest-only vs. amortizing mortgages
Some real-estate investors use interest-only mortgages, where early payments are 100% deductible (interest) with no principal reduction. This maximizes the tax deduction in the short term but increases the balloon payment or refinance risk later.
A $1 million interest-only mortgage at 6% requires $60,000 annual payments, all deductible. An amortizing 30-year mortgage at the same rate requires $5,996 monthly, of which ~$5,000 is interest in year one (but decreasing).
Interest-only mortgages are common among sophisticated real-estate investors, particularly for investment properties with strong cash flow. They maximize tax deductions while keeping debt manageable.
Flowchart: mortgage interest deduction analysis
Related concepts
Next
Property tax deductions compound the mortgage-interest benefit. But the $10,000 SALT cap limits the combined benefit of property taxes, income taxes, and mortgage interest for primary-residence owners. Understanding the SALT cap is essential for evaluating real-estate purchases in high-tax states.