What Is Cost Segregation? A Commercial Owner's Guide
By Basis Property Group | June 2026 | Approx. 6 minute read
Most commercial owners write off their building the slow way, one even slice a year for 39 years. Cost segregation is the engineering study that finds the parts of your building that wear out faster, moves them onto shorter depreciation schedules, and lets you take those deductions far sooner. Here is what it is, in plain English.
What cost segregation is
Cost segregation is an engineering-based study that breaks a building's purchase or construction cost, what the tax code calls its basis, into individual components and assigns each component its correct IRS depreciation life. Instead of treating the whole property as one slow-depreciating asset, the study recognizes that a building is really a bundle of very different things: structural shell, carpeting, cabinetry, specialty electrical, parking lots, landscaping. Those parts do not last the same number of years, and the tax code does not require you to pretend they do.
The result is a documented reallocation of basis that lets the faster-wearing components be depreciated over far shorter periods than the building itself. That timing shift is the entire point: the same total deduction, taken much sooner, is worth more because of the time value of money.
How a building gets split
By default, the IRS depreciates a commercial building straight-line over 39 years (residential rental property runs over 27.5 years). A cost segregation study leaves the structural shell on that long schedule but pulls eligible components into three shorter categories:
- 5-year property: items like carpet, certain fixtures, and equipment
- 7-year property: furnishings
- 15-year property: site and land improvements such as paving, landscaping, and exterior lighting
- 39-year property: the structural shell, roof, and core systems that remain on the standard commercial schedule
One rule sits above all of this: land is never depreciable. The study carves land out first, then works only with the depreciable building basis. How much moves into the shorter buckets depends on the property type, but reclassifying somewhere in the range of 20 to 35 percent of building basis is common.
Why it matters now
Timing is what makes cost segregation valuable, and current law amplifies that timing. Property with a recovery period of 20 years or less qualifies for bonus depreciation, and the 5, 7, and 15-year components a study identifies all fall under that ceiling. The 39-year shell does not, which is exactly why the split matters.
This pairs directly with the One Big Beautiful Bill Act of 2025, which made 100% bonus depreciation permanent for qualifying property acquired and placed in service after January 19, 2025. In practice, that means the shorter-life components a study uncovers can often be deducted in full in the first year rather than spread across decades. Cost segregation is the mechanism that exposes those components in the first place.
A simple example
Picture a building with $1,500,000 of depreciable basis (land already excluded). A study reclassifies roughly 28 percent of it, about $420,000, into shorter-life property: 5-year fixtures and equipment, 7-year furnishings, and 15-year site improvements. The remaining basis stays on the 39-year schedule. Under current bonus depreciation rules, much of that $420,000 can be deducted up front instead of over 39 years. These numbers are illustrative; your actual result depends on your property and an engineered study.
Who it is for
Cost segregation is built for owners of commercial and investment real estate: multifamily, retail, office, industrial, hospitality, medical, and similar properties held to produce income. As a rough screen, a study tends to make sense when building basis is somewhere above $300,000, because the benefit has to clear the cost of the study itself. The more a property has been built out or improved, the more there typically is to reclassify.
What it is not
Cost segregation is not a loophole or an aggressive scheme. It is a long-standing, IRS-recognized method, sanctioned since Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997), and the IRS itself publishes a Cost Segregation Audit Techniques Guide describing how a proper study should be performed. It is also not a do-it-yourself exercise. A credible study is an engineering analysis, not a spreadsheet estimate, and it produces documentation built to withstand scrutiny. And it is not a replacement for your CPA. The study supplies the component detail; your CPA files your return using it.
What to do next
You do not have to commit to anything to find out whether a study is worth it. The first step is simply to see how much of your specific building is likely to qualify for acceleration, before you spend a dollar.
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Frequently asked questions
What's the difference between 5, 7, 15, and 39-year property?
They are IRS depreciation lives. A commercial building shell is depreciated straight-line over 39 years. A study reclassifies faster-wearing parts into shorter lives: 5-year for items like carpet, certain fixtures, and equipment; 7-year for furnishings; and 15-year for site and land improvements such as paving, landscaping, and exterior lighting.
How much of my building can be reclassified?
It depends on the property type, but reclassifying roughly 20 to 35 percent of building basis into shorter-life property is common. Heavily improved properties such as restaurants and hotels tend to fall at the higher end. Land is never depreciable and is excluded entirely.
Is cost segregation IRS-approved?
Yes. The approach has been sanctioned since Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997), and the IRS publishes a Cost Segregation Audit Techniques Guide that describes how a proper engineering-based study should be conducted and documented.
Do I need a study if I already have a CPA?
Usually yes. A cost segregation study is an engineering analysis that most CPAs do not perform in-house. The study produces the component detail and supporting documentation; your CPA then uses it to file your depreciation. The two work together.
Sources
» IRS Cost Segregation Audit Techniques Guide, irs.gov
» Internal Revenue Code Section 168, accelerated cost recovery system
» Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997)
» IRS Publication 946, How to Depreciate Property
Basis Property Group is a cost segregation advisory and brokerage. It is not a certified public accounting firm or a law firm, and nothing in this article constitutes tax, legal, or accounting advice. Tax outcomes depend on an engineered study and on your individual circumstances, and are determined by you and your tax advisor.
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