Mortgage Interest Deduction: What Counts?

Include only mortgage interest and points deductible for the tax year after checking the loan’s security, use of proceeds, applicable debt limits, and payment timing. Then combine that amount with your other allowable itemized deductions and compare the result with your available standard deduction. Neither your total mortgage payments nor the amount on Form 1098 automatically equals your deductible interest. IRS Publication 936 explains the qualification and limitation rules.

Which mortgage interest belongs in the comparison?

For the federal home mortgage interest deduction, the debt generally must be secured by a qualified home in which you have an ownership interest. A qualified home can be your main home or one qualifying second home. For acquisition debt, the borrowed funds must be used to buy, build, or substantially improve the home securing that loan. You claim the deduction by itemizing on Schedule A, not by adding mortgage interest to the standard deduction.

Use the following distinctions when reviewing your annual mortgage statement and closing records:

These classifications follow Publication 936 and the Schedule A instructions. Interest attributable to business, rental, or investment use may require different treatment; do not deduct the same expense both on Schedule A and elsewhere.

A second home rented to others needs an additional qualification check. Publication 936 applies personal-use requirements before treating it as a qualified second home. A vacation-rental mortgage should not automatically be combined with interest on a personal residence.

What loan information do you need before calculating?

Start with the tax year and filing status. Then gather these records for every relevant mortgage, including loans on a second home:

• Origination date, original principal, and refinancing history.
• Loan documents identifying the property securing the debt.
• Records showing how purchase, improvement, and cash-out proceeds were used.
• Balance information needed for the average-balance methods in Publication 936.
• Forms 1098, payment statements, and closing disclosures.
• Points paid and any remaining points being deducted over a loan’s term.
• Your share of payments if another borrower also paid interest.
• Any mortgage interest credit or assistance payments affecting the deduction.

The origination date matters because different debt categories can have different limits. For tax year 2025, Publication 936 generally limits qualifying acquisition debt incurred after December 15, 2017, to $750,000, or $375,000 for married filing separately. Certain older acquisition debt falls under the higher tax year 2025 limits of $1 million or $500,000, respectively, and grandfathered debt has separate treatment. These are debt limits—not annual interest deduction allowances—and they apply across the relevant homes rather than separately to each mortgage.

For another tax year, use that year’s Publication 936 and applicable legislative updates. Do not select a limit solely from the current loan’s closing date: qualifying refinancing can preserve older debt treatment, but cash-out borrowing does not automatically inherit it. Mixed debt categories require the Publication 936 worksheet rather than a simple comparison with one headline limit.

Why doesn’t Form 1098 establish the deduction?

Form 1098 reports lender information. It does not establish how you used borrowed funds, whether another borrower paid part of the interest, or whether your combined mortgages exceed the applicable debt limits. The deductible amount therefore may differ from the reported amount.

Reconcile the statement with your records before using it:

1. Identify the interest attributable to qualifying debt.
2. Remove amounts belonging to another borrower or deducted elsewhere.
3. Apply debt limitations using Publication 936 when required.
4. Determine which points are deductible this year.
5. Account for adjustments such as refunded interest or a mortgage interest credit.

Not receiving Form 1098 does not, by itself, eliminate an otherwise allowable deduction. The Schedule A instructions explain reporting for interest not shown on Form 1098, including seller-financed mortgages and shared interest reported under another borrower’s name. Supporting records still matter.

How do HELOCs and cash-out refinancing affect eligible interest?

Follow the borrowed money, not the loan’s marketing name. Interest on a HELOC used to substantially improve the home securing it can qualify. Interest on the same HELOC used for a vacation, credit-card repayment, or other personal expenses does not qualify as home mortgage interest. Borrowing against one home to improve a different home also does not meet the same-home use requirement.

When a loan has both qualifying and nonqualifying uses, maintain records tracing each portion. An allocation based only on the original proceeds may become inaccurate after additional draws or repayments. Publication 936 addresses mixed-use mortgages and the allocation needed before calculating deductible interest.

For a cash-out refinance, separate the amount replacing existing qualifying debt from additional borrowing. Analyze the cash-out portion according to its actual use rather than treating the entire new balance as acquisition debt.

Which points can you deduct this year?

Points generally represent prepaid interest and are deducted over the loan’s term. Certain points paid to buy or build a main home can qualify for a deduction in the year paid, but only when all applicable Publication 936 tests are met. Those tests address local lending practice, the amount charged, the funds supplied at closing, and how the charge appears on the settlement statement.

The treatment differs by transaction:

Publication 936 also provides special rules when a mortgage ends early. Refinancing with the same lender can change the treatment of remaining points, so do not automatically deduct the entire unamortized balance.

Include deductible points only once. Reconcile amounts reported on Form 1098 with your separate amortization records before adding them to annual interest.

Do mortgage insurance premiums belong in the total?

Check the tax year separately from ordinary mortgage interest. For tax year 2025, Publication 936 states that the mortgage insurance premium deduction had expired. For tax year 2026, Publication 505 describes the restored deduction for qualifying premiums connected with acquisition debt under insurance contracts issued after December 31, 2006. The One Big Beautiful Bill Act changed this treatment, so the tax year 2025 exclusion should not simply be carried forward.

For a tax year 2026 comparison, determine the allowable premium deduction under the applicable Schedule A and Publication 936 instructions, including income limitations and any required allocation of prepaid premiums. Keep it separate from ordinary interest until those rules have been applied; the amount paid is not automatically the amount deductible.

How does eligible interest change the itemizing decision?

First calculate your other allowable itemized deductions. These can include qualifying state and local taxes, charitable contributions, deductible medical expenses, and other Schedule A categories. Use amounts after their respective limitations—not gross spending—and exclude anything already deducted elsewhere.

For a straightforward comparison, define all amounts in dollars for the same tax year:

• (M): allowable mortgage-related deduction, including deductible interest and points.
• (O): other allowable itemized deductions.
• (S): available standard deduction for your filing circumstances.

If both deduction methods are available, no overall itemized limitation applies, and no deduction changes with the choice:

[
I=O+M
]

[
\text{Additional deduction from itemizing}=\max(0,I-S)
]

The break-even point is (O+M=S). Mortgage interest below that point may simply replace part of the standard deduction rather than produce an additional deduction. This follows the IRS’s general rule of comparing allowable itemized deductions with the available standard deduction.

To isolate how much the mortgage deduction changes the amount selected:

[
\text{Mortgage-related increase in selected deduction}
=
\max(S,O+M)-\max(S,O)
]

This formula measures a deduction difference, not a tax saving. It also assumes that removing mortgage interest does not change any other deduction or limitation.

When does the simple comparison need adjustment?

For tax year 2026, eligible non-itemizers may claim a separate deduction for qualifying cash charitable contributions, while itemizers face a charitable contribution floor. Higher-income taxpayers may also face an overall limitation on itemized deductions. Compare the full deduction calculation under both alternatives when these provisions apply. Publication 505 provides tax year 2026 estimated-tax worksheets; use the applicable final return instructions when filing.

Also confirm that the standard deduction is available. For example, a married-filing-separately taxpayer generally cannot use it when the other spouse itemizes. The related explanation, Standard Deduction vs. Itemized: Which Should You Use?, develops the broader comparison.

Worked example: qualifying interest versus total mortgage costs

The following hypothetical example uses tax year 2026 solely to demonstrate the calculation.

Assume a married couple files jointly, both spouses are under age 65, neither is blind, neither is a dependent, and both qualify for the standard deduction. Their tax year 2026 standard deduction is $32,200 under Publication 505. Assume AGI is $150,000, no other deductions affect the taxable-income calculation, and no overall itemized limitation applies.

Their loan records show:

Assume the acquisition debt and qualifying HELOC portion remain below the applicable debt limit, the HELOC allocation remains 60% qualifying throughout the year, and all requirements for ratably deducting the refinance points are met. The couple has no deductible mortgage insurance premiums, mortgage interest credit, assistance-payment adjustment, or charitable contributions.

Step 1: Allocate the HELOC interest

[
\text{Qualifying share}=\frac{30{,}000}{50{,}000}=60%
]

[
\text{Eligible HELOC interest}=2{,}400\times60%=1{,}440
]

The remaining HELOC interest is attributable to personal spending and does not enter this home mortgage interest deduction.

Step 2: Calculate the current-year points deduction

[
\text{Deductible points}
=
\frac{3{,}600}{180}\times12
=
240
]

Only $240 enters the hypothetical tax year 2026 comparison, not the entire $3,600 paid for the refinance points. Publication 936 illustrates this ratable method using the loan term and payments made.

Step 3: Build the allowable mortgage-related deduction

[
M=18{,}000+1{,}440+240=19{,}680
]

Step 4: Compare itemizing with the standard deduction

[
I=18{,}000+19{,}680=37{,}680
]

[
I-S=37{,}680-32{,}200=5{,}480
]

Itemizing reduces taxable income by an additional $5,480 in this scenario. Although the allowable mortgage-related deduction is $19,680, its incremental deduction benefit is only $5,480 because the couple would otherwise use the standard deduction.

All example amounts and intermediate results are whole dollars, so rounding does not change the outcome. The example does not calculate final federal income tax, a refund, or state tax.

How should you interpret the comparison result?

A deduction reduces taxable income; it is not a dollar-for-dollar tax credit. Its tax effect depends on the tax calculation under both alternatives. A marginal rate may support a limited approximation when the entire difference falls within one rate band, but an effective tax rate is not a substitute for recalculating tax. Preferential capital-gain rates, alternative minimum tax, and other limitations can require additional calculations. Publication 505 provides separate methods for several of these situations.

Withholding is separate from liability. Claiming mortgage interest on a return does not itself change payroll withholding; a withholding adjustment requires a separate review of Form W-4 and the applicable instructions.

For any calculator comparison, check the selected tax year, debt-limit assumptions, and whether fields request gross payments or already-limited deductions. A simplified estimate cannot establish the use of loan proceeds, resolve missing ownership records, prepare a return, or submit an election. You remain responsible for the facts entered and for checking the result against current official instructions.

A federal result also does not establish the state result. Review your state revenue department’s instructions for the same tax year before treating the federal deduction difference as a combined federal-and-state tax benefit.