U.S. · Tax forms
Form 8829 line 16, excess mortgage interest.
Where mortgage interest goes if you take the standard deduction, and what counts as excess if you itemize.
Line 16 takes mortgage interest that line 10 cannot. If you claim the standard deduction, enter all home mortgage interest on loans used to buy, build or substantially improve the business home in column (b) of line 16. If you itemize, enter only the excess that the personal deduction limits disallow.
Look up a line 16 case
Result
Line 10 versus line 16 (2025 instructions)
| Item | Meaning | What the IRS says |
|---|---|---|
| Standard deduction | All interest on line 16 | Enter all home mortgage interest paid for loans used to buy, build or substantially improve the home in column (b) of line 16; leave line 10 blank |
| Itemizing | Line 10, then excess on 16 | Line 10 gets the deductible amount from Schedule A (Pub. 936); line 16 gets the excess attributable to the business home loans |
| Home equity loan for other uses | Not included | Do not include interest on a loan that did not benefit your home, for example used to pay off credit cards, buy a car or pay tuition |
| Column | (b) Indirect | Mortgage interest is entered in column (b); do not claim it in column (a) as a direct expense, even for a separate structure |
| Line 23 | Adds lines 16–22 | Excess mortgage interest is part of operating expenses |
| Line 24 | Line 23 (b) × line 7 | Business share of the excess interest |
The IRS example
If you paid $15,000 of home mortgage interest on loans used to buy, build or substantially improve the business home but could deduct only $12,000 on Schedule A because of the personal limits, you include $3,000 ($15,000 − $12,000) in column (b) of line 16.
Why column (b) only
The Line 10 instructions explain that the personal limits are figured using all loans secured by your homes, so mortgage interest cannot be a direct expense in column (a), even when you use a separate structure for the business.
Schedule A side
If you itemize, the personal portion of the interest you entered in column (b) of line 10 (for example 70% if your line 7 percentage is 30%) is still deductible on Schedule A.
Worked example
Rita takes the standard deduction and paid $9,000 of mortgage interest on the loan that bought her home. Her business percentage on line 7 is 15%. She leaves line 10 blank and enters $9,000 in column (b) of line 16; line 24 multiplies it by 15%, and the business share is $1,350, which then competes under the line 27 limit. Names and figures are made up.
More line pages in this set
Related lines: Form 8829 Line 11, Form 8829 Line 22, Form 8829 Line 8.
Sources
- Instructions for Form 8829 (2025): the line-by-line instructions on this page. Page last reviewed or updated April 30, 2026. Read November 2, 2026.
- Form 8829 (2025): the printed line wording and arithmetic on the form. Read November 2, 2026.
Tax year 2025 edition of Form 8829 and its instructions (page last reviewed or updated April 30, 2026). Line numbers and dollar limits are those printed in the 2025 form and instructions and can change by year. Names in worked examples are made up.
Frequently asked questions
What goes on Form 8829 line 16?
Excess mortgage interest: for standard deduction filers, all home mortgage interest on loans used to buy, build or substantially improve the business home; for itemizers, the part that exceeds what Schedule A allows.
I take the standard deduction. Do I use line 10?
No. Do not report an amount on line 10; use column (b) of line 16.
Does a home equity loan used for other purposes count?
Not if it did not benefit your home, such as paying credit cards, buying a car or paying tuition.
Can mortgage interest be a direct expense?
No. The instructions say not to claim mortgage interest in column (a), even for a separate structure.
Where can I read the Schedule A limit?
The instructions refer to Pub. 936 for the home mortgage interest deduction and its limits.
Not tax advice
This page summarizes IRS instructions, mostly written for the people who prepare the form, and is not tax, legal or financial advice. A CPA or an enrolled agent can confirm what a line means for your return. Everything runs in your browser; nothing you enter is sent anywhere.