Can the Home Office Deduction Be Bigger Than Your Side Income? The IRS Limit

No. The home office deduction cannot be larger than what your business earned from that space after its other costs, so it cannot create or deepen a loss. Under the regular (actual expense) method the part you cannot use this year carries over to a later year; under the $5-per-square-foot simplified method it is simply lost.

You can qualify for the deduction and still get little from it in a slow year. The qualifying tests and the two methods are in the simplified vs regular home office deduction guide; this post covers only the ceiling.

1. What the IRS says the limit is

Publication 587 states the limit this way: your deduction for business use of the home is limited to the gross income from the qualified business use of the home, reduced by business deductions that are unrelated to the use of the home. If those unrelated deductions are greater than the gross income, you cannot take a deduction for the home at all.

Unrelated expenses, per Publication 587, include advertising, wages, supplies, dues, and depreciation on equipment.

The IRS simplified-option page says the same in its comparison table: for both methods, the deduction "cannot exceed gross income from business use of home less business expenses."

2. How the limit works under the regular method

Publication 587 describes a two-step test for the actual-expense method.

1. If gross income from the business use of your home equals or exceeds your total business expenses (including depreciation), you can deduct all your business expenses related to the use of your home.
2. If gross income is lower than those expenses, your deduction for otherwise nondeductible home expenses, such as insurance, utilities and depreciation of the home, is limited to the gross income minus two things: the business part of expenses you could deduct anyway (such as mortgage interest and real estate taxes, if you itemize), and the business expenses that relate to the activity but not to the home (phone, supplies, equipment depreciation).

Publication 587 adds that if you are self-employed, you do not include your deduction for one-half of self-employment tax in that second subtraction. It also says depreciation of the home is taken last, so it is the first thing squeezed out.

The IRS's own example shows the order. A person with $6,000 of gross business income subtracts $3,000 of deductible mortgage interest and real estate taxes and $2,000 of business expenses unrelated to the home, which leaves a deduction limit of $1,000. Maintenance, insurance and utilities of $800 fit inside it, so only $200 of the $1,600 depreciation is allowed, and the remaining $1,400 carries over to 2026. Check: $6,000 - $3,000 - $2,000 = $1,000, and $1,000 - $800 = $200.

3. What carries over, and what does not

Publication 587 says excess business expenses for the home can be carried over to the next year in which you use actual expenses. They are subject to that year's limit, whether or not you live in the same home that year. Schedule C filers figure the limit and carryover on Form 8829.

The simplified method works differently. According to the IRS comparison table:

Publication 587 adds that a carryover from an earlier actual-expense year is not deducted in a simplified-method year. It is not erased, though: it keeps waiting for the next year you use actual expenses.

4. A worked example for a small side business

This example reuses the renter from the simplified vs regular guide: a 150-square-foot office in a 1,500-square-foot apartment, which is 10% of the home. Rent is $18,000, utilities are $2,400 and renters insurance is $300 for the year. The regular method figure is 10% x ($18,000 + $2,400 + $300) = $2,070. The simplified figure is 150 x $5 = $750.

Now suppose the side business took in $4,000 and had $3,100 of expenses unrelated to the home (software, supplies, ads). A renter has no mortgage interest or real estate taxes to subtract, so under the Publication 587 formula the limit is $4,000 - $3,100 = $900.

Two lessons come out of the numbers. First, the regular method's larger $2,070 is capped at $900, so its advantage over the simplified $750 shrinks to $150 this year. The $1,170 carryover is only worth something if a later year has enough business income to absorb it. If the business never earns that much, it never gets used.

Now change the income to $3,000 with the same $3,100 of other expenses. The gross income is smaller than the unrelated expenses, so the limit is below zero and, per Publication 587, no home deduction is allowed that year. The regular method would park the full $2,070 as carryover. The simplified method would give nothing and carry nothing.

5. What this means for choosing a method

• In a year with thin profit, compare the capped figure, not the headline figure. The IRS says you pick a method each year by using it on your timely filed original return, and you cannot switch for that year afterward, so run both numbers before filing.
• If you expect stronger income later, the regular method's carryover can preserve value. The simplified method cannot.

6. Key takeaways

• The home office deduction is capped at business gross income minus business expenses not tied to the home (IRS Publication 587).
• Regular method: the excess carries over to the next year you use actual expenses. Simplified method: the excess does not carry over.
• In the example above, a calculated $2,070 deduction is limited to $900 when income is $4,000 and other expenses are $3,100.
• If other business expenses exceed business gross income, no home deduction is allowed that year.
• Check Form 8829 instructions or a tax professional for your own numbers; this is general information, not tax advice.