How Much Mortgage Interest Is Deductible? – If you’re a US homeowner wondering “how much mortgage interest is deductible” on your 2025 tax return (filed in 2026), you’re not alone. The mortgage interest deduction remains one of the most valuable tax breaks for homeowners who itemize deductions. However, strict IRS limits apply based on when you took out your loan, how you used the proceeds, and your filing status. Thanks to the Tax Cuts and Jobs Act (TCJA) and the permanent extension under the One Big Beautiful Bill Act (OBBBA) of 2025, the rules provide long-term clarity—no reversion to higher pre-2018 limits.
This guide breaks down everything using the latest IRS Publication 936 (for 2025), so you can maximize your deduction legally and avoid costly mistakes.
What Is the Mortgage Interest Deduction?
The mortgage interest deduction lets you subtract qualified home mortgage interest from your taxable income when you itemize on Schedule A (Form 1040). It applies only to interest paid on a secured loan for your main home or a second home—not personal loans or unsecured debt.
You must:
- Itemize deductions (the standard deduction for 2025 is $15,750 single / $31,500 married filing jointly, so run the numbers).
- Have ownership interest in a qualified home.
- Pay interest on a secured debt (mortgage, deed of trust, etc.).
Not all interest qualifies—proceeds must generally go toward buying, building, or substantially improving the home.
Who Qualifies for the Mortgage Interest Tax Deduction?
To claim any mortgage interest deduction in 2026:
- You file Form 1040 or 1040-SR and itemize.
- The loan is secured by your qualified home (house, condo, co-op, mobile home, boat, etc., with sleeping, cooking, and toilet facilities).
- You have an ownership interest and the lender intends repayment.
- For home equity loans/HELOCs: Proceeds must buy, build, or substantially improve the securing home (this rule is now permanent).
Second homes qualify if you designate one as your second home for the year. Cooperatives have special stock-based rules.
Current Mortgage Interest Deduction Limits for 2026
The IRS caps the amount of debt on which you can deduct interest. These limits are now permanent following the OBBBA:
- Loans taken out after December 15, 2017: Deduct interest on up to $750,000 of qualified debt ($375,000 if married filing separately).
- Loans taken out before December 16, 2017 (grandfathered): Deduct interest on up to $1 million of qualified debt ($500,000 if married filing separately).
The limits apply to the combined debt on your main and second homes. They are not indexed for inflation.
Important: Recent legislation made the $750,000 cap permanent, eliminating any scheduled increase back to $1 million after 2025.
Mortgage Interest Deduction for Pre-2018 Loans (Grandfathered Debt)
If your mortgage originated on or before October 13, 1987, or qualifies under the 1987–2017 window (with exceptions for binding contracts), you may use the higher $1 million limit. Refinancing older debt generally preserves grandfathered status up to the original principal.
This higher limit phases in with newer debt and reduces the room available under the $750,000 cap.
How Home Equity Loans and HELOCs Affect Your Deduction?
Home equity interest is only deductible if the borrowed funds are used to buy, build, or substantially improve the home that secures the loan. This restriction (introduced by TCJA and made permanent) means:
- Cash-out refinances for vacations, debt consolidation, or other personal uses → not deductible.
- Home equity used for kitchen remodel or addition → deductible (subject to overall limits).
Mixed-use loans require allocation of balances and interest.
How to Calculate Your Deductible Mortgage Interest If You Exceed the Limits?
If your total mortgage balances exceed the applicable limit, you cannot deduct 100% of the interest. Use the Worksheet in IRS Publication 936, Table 1 to figure your qualified loan limit and prorated deductible interest:
- Calculate average balances for each debt type (grandfathered, pre-2018 acquisition, post-2017 acquisition).
- Apply the limits step-by-step.
- Multiply total interest paid by the ratio of qualified limit to total average debt.
Example: If your average debt is $900,000 but your qualified limit is $750,000, you deduct about 83% of the interest paid ($750k ÷ $900k).
Three methods exist for average balance: first/last balance, interest-paid ÷ rate, or monthly lender statements. Use the one that fits your situation.
Points paid at closing are also prorated under the same ratio (or fully deductible in some cases for main-home purchase).
What Counts as Qualified Home Mortgage Interest?
- Interest on acquisition debt for buying, building, or substantially improving your home.
- Late payment charges (if treated as interest).
- Prepaid interest (allocated over time, except points).
Not deductible:
- Interest on debt used for non-home purposes.
- Mortgage insurance premiums (in most cases; check for limited post-2025 relief).
- Fees, property taxes, or principal payments.
How to Report Mortgage Interest on Your Tax Return?
- Form 1098: Your lender reports interest in Box 1. Enter on Schedule A, Line 8a.
- Additional deductible interest not on 1098 → Line 8b (attach statement).
- Points not on 1098 → Line 8c.
- Attach Form 8396 if claiming a mortgage interest credit.
Keep records of loan origination dates, proceeds use, and average balances.
Common Mistakes to Avoid with Mortgage Interest Deduction
- Claiming interest on home equity used for non-home purposes.
- Forgetting to prorate when debt exceeds limits.
- Using the standard deduction when itemizing (including mortgage interest + property taxes + charitable gifts) would save more.
- Missing the binding-contract exception for 2017–2018 loans.
- Not tracking mixed-use loans properly.
Frequently Asked Questions About Mortgage Interest Deductibility
Can I deduct mortgage interest on two homes?
Yes—limits apply to the combined debt.
What if I refinance?
Refinanced acquisition debt keeps the original date’s limit up to the prior balance.
Does this apply to investment properties?
No—rental properties use different rules (Schedule E).
Are there state tax differences?
Federal rules apply for federal taxes; some states conform differently—check your state.
Maximize Your Mortgage Interest Deduction in 2026
The mortgage interest deduction can save thousands in taxes, but only if you understand the IRS limits and rules in Publication 936. For most homeowners with mortgages originated after 2017, the permanent $750,000 cap ($375,000 MFS) applies—plan accordingly when buying or refinancing.
Tax laws are complex and subject to change. Always consult a qualified tax professional or use IRS.gov tools for your specific situation. Download the latest Publication 936 and Schedule A instructions directly from the IRS website for worksheets and examples.
By staying informed, you can confidently claim every dollar of mortgage interest you’re entitled to while staying fully compliant.