If you work from home and use part of it exclusively for business, the IRS gives you two ways to turn that space into a deduction: a flat, no-receipts simplified method, or an actual-expense method that prorates your real housing costs. Most people never compare them — they just default to whichever one their tax software suggests first. This calculator runs both methods side by side on your numbers, tells you which one wins, and estimates the tax you'd actually save by claiming it.
How it works
The simplified method multiplies your qualifying office square footage by a flat IRS rate of $5, capped at 300 square feet — so the most this method can ever produce is $1,500. No receipts, no depreciation schedules, just square footage times a fixed rate.
The actual expense method instead prorates your real home costs. Add up your annual rent or mortgage interest, utilities, homeowners or renters insurance, and repairs for the whole home, then multiply that total by the fraction of your home's square footage the office occupies (office square feet ÷ total home square feet). There's no cap on this method beyond the math itself — a larger office in an expensive home can produce a much bigger deduction than the simplified method's $1,500 ceiling.
The calculator computes both methods from your inputs and reports the larger of the two as your recommended deduction, since nothing stops you from picking whichever number is bigger (you just can't mix both methods in the same tax year). It then multiplies that recommended deduction by the marginal tax rate you supply to estimate the actual dollars it saves you — a deduction only helps to the extent it's taxed away, so a $2,000 deduction at a 22% marginal rate saves $440, not $2,000.
Worked example
Say you have a 200 sqft home office in a 2,000 sqft home, your total annual home expenses (rent, utilities, insurance, repairs) run $20,000, and your marginal tax rate is 22%.
- Simplified method: 200 sqft × $5 = $1,000
- Actual method: (200 ÷ 2,000) × $20,000 = 10% × $20,000 = $2,000
- Recommended deduction: the larger of the two = $2,000
- Estimated tax saved: $2,000 × 22% = $440
Here the actual expense method wins by a wide margin, because the home's overall costs are high relative to its size. Flip the ratio — a small office in an inexpensive home — and the flat $5/sqft simplified method often comes out ahead instead, especially once the office is anywhere near the 300 sqft cap.
How to interpret your result
The recommended deduction is whichever method produced the bigger number for the figures you entered — the calculator picks it for you so you don't have to run both by hand. The simplified and actual method figures are both shown so you can see how close the comparison was and sanity-check the inputs (a huge gap between the two often means the "total home expenses" figure needs a second look).
Estimated tax saved is a first-order estimate, not a guarantee: it applies your stated marginal rate directly to the deduction, without modeling bracket boundaries, phase-outs, the standard deduction, or how self-employment tax interacts with your overall return. Treat it as a "worth roughly this much" figure, not a line you can copy straight onto a return.
Remember also that you must actually elect a method when you file — the IRS does not let you claim the simplified method one line and the actual method on another for the same tax year, and once you've chosen for a given year you can't switch retroactively. If your actual and simplified figures are close, factor in how much recordkeeping you're willing to do: the simplified method needs none, while the actual method requires you to substantiate every expense you prorate.
This tool covers only the federal home office deduction and only for US taxpayers; it does not address state-specific rules, and it is not a substitute for a tax professional or IRS guidance.
Methodology & sources
Simplified method: min(officeSqft, 300) × $5. Actual method: (officeSqft ÷ homeSqft) × totalHomeExpenses, guarded against a zero or negative home square footage. Recommended deduction is max(simplified, actual); estimated tax saved is recommendedDeduction × (marginalRatePercent ÷ 100).
The $5-per-square-foot rate and 300-square-foot cap come from the IRS's safe harbor under Rev. Proc. 2013-13, unchanged since it took effect for the 2013 tax year. See the IRS's own page, Simplified option for home office deduction, for the full rules on eligibility, the "regular and exclusive use" test, and how to elect a method.