Is mortgage interest on a building you use in the business line 16a or line 16b?

Mortgage interest paid to anyone other than a bank or similar institution goes on line 16b, not 16a.

Is mortgage interest on a building you use in the business line 16a or line 30?

If the mortgaged property is the home you live in, the business share runs through Form 8829 and line 30 rather than line 16a.

Where does business mortgage interest go? Line 16a

Short answer Schedule C, Line 16a Interest, mortgage (paid to banks, etc.)

Mortgage interest on a building you use in the business belongs on Line 16a, interest, mortgage.

Why line 16a

Line 16a is the one line for mortgage interest on real property used in the business and paid to banks or similar financial institutions. A loan on a workshop, office unit or warehouse you own and operate from fits it exactly. If the lender is not a financial institution, a seller carrying the note for example, the interest is still deductible but is reported on line 16b instead.

Stop looking up lines one at a time. ClaryBook totals your year into an IRS Schedule C worksheet in form order, Part I and Part II line by line, so mortgage interest on a building you use in the business lands on Line 16a without you sorting it.

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What mortgage interest on a building you use in the business is confused with

Line 16b, interest, other: Mortgage interest paid to anyone other than a bank or similar institution goes on line 16b, not 16a.
Line 30, line 30, business use of your home: If the mortgaged property is the home you live in, the business share runs through Form 8829 and line 30 rather than line 16a.
Schedule E, schedule e, rental real estate: If you rent the building out instead of operating from it, the interest belongs on Schedule E.

Examples that belong on line 16a

$9,400 of interest on a commercial mortgage on the unit your shop occupies
Interest on a bank loan secured by a detached studio building used only for the business
$6,100 of interest on a mortgaged warehouse where you store and pack inventory
The business-only share of interest on a mixed-use building where you occupy the ground floor

What does not belong here

Interest on your residence, which runs through the home office calculation
Principal payments
Property taxes on the building, which are line 23
Interest on a mortgage for a rental property, which is Schedule E

What to keep

Keep the lender's Form 1098 or annual statement, the note, and the deed showing the property and how the business uses it.

Related lookups

Sources

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.

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