Home mortgage interest where you have a home office belongs on Line 30, line 30, business use of your home.
Why line 30
Mortgage interest on the home you live in does not go on line 16a even when a room is your office. It is an indirect expense on Form 8829, where your business use percentage is applied and the result carries to line 30. The remaining share stays available as a personal itemized deduction on Schedule A, so the Form 8829 route splits the interest rather than losing it.
Log it once, with the line already on it. Type an expense in plain words in ClaryBook and it is filed with a date, vendor, amount and what it was for, so the number your preparer needs for home mortgage interest where you have a home office is already written down.
Start for freeWhat home mortgage interest where you have a home office is confused with
- Line 16a, interest, mortgage
- Line 16a is for mortgage interest on property used in the business, not on the home you live in; a home office sends the interest through Form 8829 instead.
- Schedule A, schedule a, personal itemised deduction
- The non-business share of home mortgage interest is itemized on Schedule A, and if you take the standard deduction that share is simply unused.
Examples that belong on line 30
- $11,000 of home mortgage interest at a 12 percent business use percentage, giving $1,320 on Form 8829
- A detached garage studio measured at 15 percent of the home's area, applied to the interest
- Interest allocated by square footage for a 140 square foot office in a 1,600 square foot house
- A second mortgage on the same home, allocated the same way
What does not belong here
- Line 16a, which is the most common mistake here
- The full interest as a business expense
- Any allocation at all under the simplified method, which is a flat rate per square foot
- Interest on a home equity loan you spent on personal things
The limit that applies
The home office deduction is capped by the gross income limit on Form 8829, and the simplified method replaces the allocation with a flat rate per square foot.
What to keep
Keep Form 1098, the square footage of the office and of the whole home, and proof the space is used only for business.
Other expenses on line 30
| Expense | Line |
|---|---|
| a home's electricity bill with a home office | Line 30 |
| home costs for a home office | Line 30 |
| homeowner's or renter's insurance with a home office | Line 30 |
| renting a room in your own home to your business | Line 30 |
| the simplified home office method | Line 30 |
| working from home | Line 30 |
Related lookups
Sources
- Publication 587, Business Use of Your Home
- About Form 8829, Expenses for Business Use of Your Home
- Instructions for Schedule C (Form 1040)
This page explains how Schedule C lines work. It is general information, not tax advice for your situation. If an expense is large or the answer turns on a fact about your business, confirm it with your tax preparer.
Looking for a different expense? The full Schedule C line lookup has every line from 8 to 27 with the expenses that belong on each, and Schedule C expense categories walks the whole form in order.
Log it once, with the line already on it. Type an expense in plain words in ClaryBook and it is filed with a date, vendor, amount and what it was for, so the number your preparer needs for home mortgage interest where you have a home office is already written down.
Start for free