Home Office Deduction for Contractors: Square Footage, Simplified Method, and What the IRS Actually Requires

A general contractor spends the day on the job site and the evening at the kitchen table writing bids, ordering materials, and chasing payments. A specialty sub runs estimates from a spare bedroom and stores tools in the garage. Both of them can take the home office deduction under IRC 280A, and for many contractors it’s one of the most overlooked write-offs on the return. The deduction converts a portion of your rent or mortgage interest, property taxes, utilities, insurance, and maintenance into a business expense, and it creates a second deduction for the business mileage from your home office to the first job site of the day (a commute without a home office isn’t deductible at all). The rules aren’t complicated, but they’re specific, and the IRS has denied the deduction often enough on audit that getting the details right matters.

Do contractors qualify for the home office deduction?

Almost always, yes. The two requirements under IRC 280A(c) are regular and exclusive use and principal place of business. Here’s why contractors clear both.

Regular and exclusive use means the space is used for business on a consistent basis and not for anything else. A spare bedroom where you keep your plans, laptop, and files qualifies. The dining room table where your kids do homework after you finish your bids doesn’t. The IRS looks for a defined space with a business purpose, not occasional use of common areas. You don’t need a separate room, but you do need a clearly identifiable area that’s dedicated to the business.

The storage exception is worth knowing about. If you store inventory, tools, or supplies at home (think: spare parts, fasteners, small power tools, safety equipment), the area where they’re stored qualifies under IRC 280A(c)(2) even without the exclusive-use test, as long as your home is the sole fixed location of the business and the storage is in a “separately identifiable space” used on a regular basis. A dedicated shelf or section of the garage counts.

Principal place of business used to be the hard test for contractors. The IRS argued that the job site was the principal place, and it won in Commissioner v. Soliman (1993). Congress fixed it in 1999 by amending 280A to add a management-activities test: a home office qualifies if the taxpayer uses it “for the administrative or management activities of any trade or business” and “there is no other fixed location of such trade or business where the taxpayer conducts substantial administrative or management activities.” A contractor who handles bidding, bookkeeping, project management, and client communication from a home office, with no separate rented office space, meets this test squarely.

Simplified method vs. regular method: which one saves more?

The IRS offers two methods, and you can switch between them year to year.

Simplified method

Introduced in 2013 as a safe harbor, the simplified method gives you $5.00 per square foot of the home office area, up to a maximum of 300 square feet. That’s a $1,500 ceiling. You don’t have to calculate actual expenses, track utility bills, or depreciate the home. You still deduct mortgage interest and property taxes on Schedule A as itemized deductions (they don’t get reduced by the business percentage). The calculation takes one line on Schedule C.

The appeal is simplicity. The limitation is the cap. If your home expenses are significant (a large house, high utility bills, substantial maintenance costs), $1,500 barely scratches the surface.

Regular method

The regular method deducts the actual business-use percentage of allowable home expenses. You calculate the percentage by dividing the square footage of your office by the total square footage of the home (or you can use a room-count method if the rooms are roughly equal in size). Then you apply that percentage to:

• Mortgage interest (or rent, if you’re a renter)
• Real estate taxes
• Homeowner’s insurance
• Utilities (electric, gas, water, internet, phone)
• Repairs and maintenance that benefit the entire home
• Depreciation on the home (the structure, not the land)

Expenses that benefit only the office (a built-in desk, rewiring an outlet for your printer, painting the office) are 100% deductible. Expenses that benefit only a non-business area (new carpet in the master bedroom) aren’t deductible at all.

Expense category	Simplified	Regular
Mortgage interest / rent	Claimed on Schedule A (no reduction)	Business % on Schedule C; remainder on Schedule A
Property taxes	Claimed on Schedule A (no reduction)	Business % on Schedule C; remainder on Schedule A
Utilities	Not deducted as home office	Business % deductible
Insurance	Not deducted as home office	Business % deductible
Depreciation	None (no recapture risk)	Business % of the home’s basis, depreciated over 39 years
Repairs (whole home)	Not deducted as home office	Business % deductible
Cap	$1,500	No cap (limited to business income)

What about the mileage deduction from a home office?

This is where the home office deduction creates a secondary benefit that many contractors miss entirely. Without a home office, your drive from home to the first job site of the day is a personal commute, and commuting miles aren’t deductible. With a qualifying home office, your home becomes your principal place of business, and the drive from your home office to the job site is a business trip. So is the drive home at the end of the day.

For a contractor who drives 30 miles each way to a job site, 250 days a year, that’s 15,000 additional deductible miles. At the 2025 standard mileage rate of $0.70 per mile, that’s $10,500 in deductions, on top of the home office deduction itself. The mileage benefit alone can exceed the home office deduction by a factor of five or more.

The same logic applies if you use the actual expense method for your vehicle instead of the standard mileage rate. The home-to-site miles become business miles in the ratio, increasing the deductible percentage of your fuel, insurance, maintenance, and depreciation.

What records do I need to keep?

The IRS has denied home office deductions on audit for lack of documentation more than for any substantive failure. Keep these:

• A floor plan or measurement showing the office area and the total home area. A simple sketch with dimensions is fine. Measure once and keep it in your records.
• Expense records for every category you’re deducting: mortgage statements, utility bills, insurance declarations, repair receipts. For the regular method, you need the full-year total for each category.
• A log showing regular and exclusive use. The IRS doesn’t require a daily diary, but if audited, you’ll need to show the space is used consistently for business. Photos of the office setup, a calendar showing when you worked from the office, and business records created at home (bids, purchase orders, invoices) all support the claim.
• Mileage records for every business trip from the home office to a job site or supplier. The IRS requires contemporaneous records: date, destination, business purpose, and miles. A log kept after the fact doesn’t count.

For the regular method, you’ll also need the home’s cost basis (purchase price plus improvements, minus land value) for the depreciation calculation. Your closing statement from the home purchase has this, and the county assessor’s breakdown of land vs. improvement value helps separate the two.

Does the deduction work for S-Corp owners?

It does, but the mechanics change. If your construction business is an S-Corp, you’re an employee of the corporation, and employees can’t deduct home office expenses on their personal returns (the TCJA suspended the employee business expense deduction through 2025). Instead, the S-Corp reimburses you for the business use of your home under an accountable plan, and the reimbursement is deductible by the corporation and tax-free to you.

The accountable plan needs three things: a business connection (the home office must meet the same 280A requirements), substantiation (the same records described above), and return of excess reimbursements. Have the S-Corp adopt a written home office reimbursement policy, calculate the deduction using the regular method, and reimburse yourself monthly or quarterly. The corporation deducts the payment as rent expense, and it doesn’t show up on your W-2.

What should I do next?

If you run any part of your contracting business from home (bidding, estimating, bookkeeping, project management, client calls), you almost certainly qualify for the home office deduction. Start by measuring the space, then run the numbers both ways (simplified vs. regular) to see which saves more. Don’t skip it because the direct deduction seems small. The mileage reclassification is usually worth more than the deduction itself.

• The construction deductions guide covers every other expense you should be writing off, including vehicles, tools, and materials.
• The entity structure guide explains when the S-Corp election makes sense and how it changes the home office mechanics.
• Quarterly payments on estimated taxes change when your deductions change: the estimated tax guide walks through the safe harbor calculation.
• If you carry insurance premiums paid from home, those are a separate deduction on top of the home office.

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.