The Home Office Deduction, Explained

The arithmetic behind the home office deduction is trivial: measure a room, divide by the size of the house, apply that percentage to your housing costs. Whether you are entitled to any of it is the hard part, and it is worth settling before running any numbers at all.

Exclusive use is where most claims fail

Three tests, and the second is the one that disqualifies people.

Regular use — the space is used for business on a continuing basis, not occasionally.

Exclusive use — the space is used only for business, with no meaningful personal use.

Principal place of business, or a place where you regularly meet clients. For most self-employed people working from home, the first applies.

A spare bedroom that is nothing but an office qualifies. The same room with a guest bed used twice a year generally does not. The dining table where you work during the day and eat dinner at night does not, however many hours you put in at it.

It does not have to be an entire room — a clearly delineated portion of one can satisfy the test — but exclusivity is binary, and it is what an examiner actually asks about.

One important boundary: employees are treated very differently from the self-employed, and employee deductions for unreimbursed expenses have been sharply restricted in the US. If you work from home for an employer, check the current rules before assuming anything — and ask about an accountable reimbursement plan, which is generally better for both parties than a deduction would have been.

Two methods

Simplified pays a flat rate per square foot up to a square-footage cap. No expense records, no depreciation, no allocation. You measure the room and multiply.

Actual takes your real housing costs and deducts the business-use share of them.

The trade is exactly what it sounds like — the simplified method trades money for effort — and how much money depends almost entirely on your rent or mortgage interest.

The home office calculator runs both at once and shows which wins, because the answer is not obvious and it flips on realistic inputs.

Business-use percentage, and the two kinds of expense

Office square footage divided by total home square footage. A 180 sq ft office in an 1,800 sq ft home is 10 percent.

That percentage applies to indirect expenses — costs of running the whole house:

• Rent, or mortgage interest (not principal — principal is not an expense)
• Property tax
• Utilities: electricity, gas, water, internet
• Homeowner's or renter's insurance
• General repairs and maintenance
• Depreciation, for owners

Direct expenses are different and are counted at 100 percent. Painting the office, a dedicated phone line, a repair to that room alone — these benefit only the business space, so no allocation applies. People routinely prorate these by mistake and give away most of the deduction.

Which method wins

The pattern is consistent once you see it.

Simplified wins when the office is small and housing is cheap. The cap means the deduction stops growing past a certain size, so a large office gets no extra benefit while the actual method keeps scaling.

Actual wins when rent or mortgage interest is high, when the office is large relative to the home, or when utilities are substantial. In an expensive metropolitan rental, 10 percent of a large annual housing cost dwarfs any per-square-foot flat rate.

In the calculator's default scenario — 180 sq ft in an 1,800 sq ft home at $24,000 a year in rent — actual wins by a wide margin. Drop the rent to $9,000 and it flips.

The depreciation trap for homeowners

Here is the consideration that does not show up in this year's deduction and should still influence the choice.

Under the actual method, homeowners depreciate the business-use portion of the house. That depreciation reduces your adjusted basis, and when you sell it is generally recaptured — taxed, often at a rate above long-term capital gains.

Worse, as with rental depreciation, the recapture generally applies to depreciation you were allowed to claim, whether or not you claimed it.

The simplified method involves no depreciation at all. Which makes it quietly attractive for a homeowner in an appreciating market who intends to sell, independent of which method gives the bigger number this year. The capital gains estimator shows how basis adjustments flow through to a sale.

Renters do not have this problem, which is one reason the actual method is an easier call for them.

The audit-risk myth

The home office deduction has a folk reputation as an audit magnet. It is largely outdated. The deduction is common, the simplified method exists specifically to make it accessible, and claiming something you are entitled to is not a red flag.

What is a red flag is a claim that would not survive the exclusive-use question, or a business-use percentage that does not describe a home anyone would recognise. Measure the room, take a photo, keep the lease or mortgage statement. Then the claim is boring, which is the goal.

It pairs with the vehicle question

One consequence worth knowing: if your home is your principal place of business, trips from home to clients and job sites generally stop being commutes and start being deductible business miles.

That single fact often makes the home office question and the vehicle question two halves of the same decision. The mileage vs actual expenses calculator covers which vehicle method comes out ahead, and commuting versus business travel is the distinction that matters most there too.

What the calculator leaves to you

The rate and the cap are inputs, so the page stays correct in any year. Also not modelled: the deduction limit, which generally caps the home office deduction at business income and carries the excess forward; depreciation calculation for owners; separate structures, which have their own and often more favourable rules; and the specific exceptions for daycare providers and storage use.

State treatment does not always follow federal either.

For the current rules, the IRS publishes guidance on the home office deduction and Publication 587, which walks through the tests with examples. If you are newly self-employed, the estimated tax calculator covers the other half of the year's admin.