IRS Form 8829 Instructions: Line-by-Line Guide to Home Office Expenses

Form 8829 is the IRS form for calculating home office expenses using the regular (actual expenses) method. If you're self-employed and want to deduct more than the $1,500 simplified method cap, this is the form you fill out. Here's how it works, section by section.

Part I: Calculating Your Business-Use Percentage

Part I asks for two numbers: the square footage of your home office and the total square footage of your home. The form divides them to produce your business-use percentage — the core ratio that drives every calculation that follows.

Line 1: Area of your home office in square feet. Measure the floor area of the dedicated space only. If it's an irregular room, break it into rectangles, calculate each, and add them together.

Line 2: Total area of your home. Count finished square footage only — exclude unfinished basements, garages, and attics unless they're permanently converted to living space.

Line 3: Divide Line 1 by Line 2. This is your business-use percentage.

Two notes: First, if you use more than one space in your home for business, you can combine them, but each must independently pass the exclusive-use test. Second, if you used the space for business for only part of the year (say, you started your business in July), the form asks you to adjust the calculation for the number of months in use.

Part II: Deductible Expenses

Part II is where the actual deduction takes shape. The form divides expenses into direct expenses (100% deductible) and indirect expenses (multiplied by the business-use percentage from Part I).

Columns: Each line has two columns — Column A for direct expenses, Column B for indirect expenses.

Line 9 — Casualty losses: Only relevant in specific federally declared disaster situations. Most filers leave this blank.

Line 10 — Deductible mortgage interest: For homeowners using the regular method. Enter the full annual mortgage interest here. The form will calculate the deductible portion. Important: the business-use portion claimed here must be subtracted from the total you deduct on Schedule A (Itemized Deductions), Line 8b — you cannot claim the same interest dollars twice.

Line 11 — Real estate taxes: Same treatment as mortgage interest. Enter total; the business-use portion is deducted here, the remainder on Schedule A. Under current law (OBBBA), the SALT deduction cap on Schedule A has increased to $40,000, giving homeowners more room on the personal side.

Line 12 — Excess mortgage interest: Used when your mortgage exceeds the IRS limit for deductible interest ($750,000 for loans originating after 2017). Most residential borrowers won't use this line.

Lines 14–19 — Indirect expenses not on lines 10–12: This is where you enter utilities, insurance, repairs, and other household operating costs. These are multiplied by your business-use percentage from Part I.

Lines 20–21 — Repairs/maintenance and depreciation: Direct repairs to the office space go in Column A (Line 20) at 100%. For depreciation, see Part III (covered below).

Lines 22–26 — Summary and gross income limit: The form adds up allowable deductions, then applies the gross income limitation. Your total home office deduction cannot exceed your gross income from the business, minus all other Schedule C expenses. If your deduction exceeds that limit, Part IV carries the excess forward.

Part III: Calculating Depreciation

Part III is required for homeowners using the regular method. It calculates the annual depreciation deduction on the home office's share of the building.

Line 35: The smaller of the fair market value of your home on the date the office was first placed in service, or your adjusted basis (purchase price + capital improvements).

Line 36: The value of the land. Land is not depreciable. If your tax assessment doesn't break out land separately, a common approximation is 20% of total property value — but use the actual assessment if you have it.

Line 37: Subtract Line 36 from Line 35. This is the depreciable building basis.

Line 38: Multiply by your business-use percentage from Part I. This is the home office's depreciable basis.

Line 40: Apply the IRS depreciation percentage for the applicable year. For most filers using the straight-line method over 39 years, the annual rate is 2.564% (first and last partial years are slightly less under the mid-month convention).

Line 41: The annual depreciation deduction.

This depreciation carries to Line 22 in Part II and factors into the overall deduction.

Important: if you used the simplified method in any prior year, you may have suspended carryover losses. Those carryovers cannot be used in a year when you elect the simplified method — they sit dormant until you return to the regular method.

Part IV: Carryover of Unallowed Expenses

If Part II's gross income limitation capped your deduction this year, Part IV tracks the excess. It shows how much of each expense category — operating expenses and depreciation — gets carried forward to reduce taxes in future years when business income is higher.

This carryover is indefinite. It doesn't expire. For businesses in early years with modest income, these carryforwards can become a meaningful deduction bank.

Simplified vs. Regular: Which One to Choose

The choice isn't permanent — you can switch each year. Here's when each typically makes sense:

Choose simplified when:

• Your office is 300 sq. ft. or smaller and actual expenses wouldn't exceed $1,500
• You own your home and want to avoid depreciation recapture on eventual sale
• You're in a startup year with complex bookkeeping and want to reduce the filing burden
• You plan to sell your home soon and want to minimize unrecaptured Section 1250 gain

Choose regular when:

• You rent and pay $1,200+/month — rent allocation alone likely exceeds the $1,500 cap
• Your office is large and actual expenses are substantial
• You have significant home maintenance costs or made capital improvements
• You're a homeowner planning to hold the property for 20+ years (the tax savings now outweigh the future recapture)

A side-by-side comparison using real numbers is more useful than any rule of thumb. The Home Office Tax Deduction Guide includes a worksheet that models both methods against your actual household expenses and lets you see the difference immediately.

Home Office Deduction vs. the Standard Deduction

One common confusion: the home office deduction is completely separate from the standard deduction vs. itemizing decision. Here's why:

The home office deduction is an above-the-line deduction on Schedule C. It reduces your adjusted gross income before you even reach the standard/itemize question. It lowers both your income tax and your self-employment tax on Schedule SE.

The standard deduction ($16,100 single / $32,200 joint in 2026) and itemized deductions live on Schedule A. They're mutually exclusive — you pick whichever is higher.

The home office deduction lives on Schedule C. Most self-employed individuals who claim it still take the standard deduction. The two coexist.

The wrinkle: if you're a homeowner using the regular method, the business-use portion of your mortgage interest and property taxes is claimed on Form 8829 (Schedule C). The personal portion is claimed on Schedule A. If you're taking the standard deduction, you can't also claim that personal portion — but the business portion on Form 8829 still stands regardless.

For homeowners who itemize, this creates a planning situation: claiming more business-use percentage shifts expenses from Schedule A to Schedule C, which is generally better (it reduces SE tax), but it also reduces your Schedule A deductions. Run both scenarios before filing.