If you use part of your home regularly and exclusively for business, you may be eligible for a home office deduction — but calculating it correctly requires the right square footage math and expense allocation. This worksheet walks through both.
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The home office deduction has specific eligibility rules — regular and exclusive business use — and the calculation itself requires accurately allocating a percentage of shared home expenses. Getting either piece wrong either costs you a legitimate deduction or creates risk if the space doesn’t actually qualify.
Download and open in Excel or Google Sheets
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Measure your home office and total home square footage
This is the basis for the business-use percentage calculation.
Enter your home expenses for the year
Utilities, insurance, and mortgage interest or rent are commonly included.
Review the automatic deduction calculation
This applies your business-use percentage to the relevant home expenses.
Run the built-in AI prompt to review eligibility
Attach the saved file to ChatGPT or Claude and ask whether your setup sounds like it meets the general eligibility criteria — then confirm with a tax professional.
Built-in AI prompt
Once you've filled this template in, it includes a ready-to-use prompt at the bottom of the sheet. Attach your saved file to ChatGPT, Claude, or any AI chat tool and paste it in — you'll get plain-English feedback on whether your home office setup sounds like it meets typical eligibility criteria for the deduction, and what to confirm with a tax professional, no accounting background required.
Claiming a space that isn’t used exclusively for business
A room used for both business and significant personal purposes generally doesn’t qualify — the space needs to meet the regular and exclusive use standard.
Measuring square footage inaccurately
The business-use percentage calculation depends directly on accurate measurements — remeasure rather than estimating.
Forgetting to include all eligible shared expenses
Utilities, insurance, and other shared home costs are often only partially remembered — a complete list produces a more accurate deduction.
Not choosing between the simplified and regular method deliberately
Tax authorities in some jurisdictions offer both a simplified flat-rate method and a detailed actual-expense method — compare both rather than defaulting to one without checking.
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