What Is Cost Segregation?
Cost segregation separates the cost of a building into components with different tax recovery periods, so parts of the property can be depreciated faster than the building itself. Land stays out of depreciation. The study prices each component and documents the class it belongs in.
Educational information, not tax advice.
Updated 2026-10-14
Key takeaways
- Federal tax law depreciates a residential rental building over 27.5 years and a nonresidential building over 39 years.
- Some of what you paid for is not the building: equipment, certain finishes, and site work can have 5-, 7-, or 15-year lives.
- A study identifies those components, prices them, and documents why each belongs in its class.
- Cost segregation changes when deductions are taken, not the total amount of depreciable basis.
- Publication 5653 is an examiner guide. It is not law and does not make any study “IRS-approved.”
When you buy or build a commercial or rental property, the default is to treat almost everything except the land as one asset: the building. Under the Modified Accelerated Cost Recovery System (MACRS), that building is depreciated in equal amounts over 27.5 years if it is residential rental property, or 39 years if it is nonresidential.
Cost segregation is the process of looking inside that single number. A building purchase or construction cost usually includes items that the tax rules treat differently: tangible personal property such as appliances, removable floor coverings, and equipment hook-ups, and land improvements such as paving, fencing, and landscaping. Those items can be depreciated over much shorter periods, which moves deductions into earlier years.
Section 167 allows a depreciation deduction for property used in a trade or business or held for the production of income. Section 168 then supplies the method, recovery period, and convention. Cost segregation does not invent a fourth rule. It applies those two sections to the pieces that make up the project instead of treating the improvement as one building.
The output is a written allocation of depreciable basis. Each line has a cost, a recovery class, and a reason. The sum of the lines must equal the depreciable basis of the property after land is removed. A study that does not reconcile to that number cannot be tested against the records.
Classification is fact-specific. An item is not personal property just because it can be unscrewed, and local fixture law does not decide the federal tax question. The regulations and decades of case law set the tests. Educational information, not tax advice.
What a study produces
A cost segregation study is a written analysis, usually prepared with engineering methods, that lists each component, assigns it a cost, places it in a MACRS recovery class, and explains the legal reasoning for that class. The total of all components must reconcile back to the property's cost basis.
The IRS has said it has not set any required format or preparer qualification for studies. Its Cost Segregation Audit Techniques Guide does describe what examiners look for, including use of original cost records, a site inspection, and a clear explanation of the analysis.
A typical report also states the placed-in-service date it relied on, how land was valued, and which documents were missing. Those assumptions matter because a later change in any of them can change the allocation your CPA posts to the depreciation schedule.
What it is not
Cost segregation does not create new deductions. The total depreciation over the life of the property is the same; the study changes when it is taken. When the property is sold, depreciation taken on personal property is generally recaptured as ordinary income under §1245.
Classification is fact-specific. An item is not personal property just because it can be unscrewed, and local fixture law does not decide the question. The regulations and decades of case law set the tests.
A study is also not a guarantee of a particular first-year deduction. Bonus depreciation, §179, state conformity, and whether you can use the extra deductions this year are return questions for your CPA.
Why it matters now
Many shorter-lived components also qualify for bonus depreciation. As of October 16, 2026, federal law allows 100% additional first-year depreciation for qualified property acquired after January 19, 2025, which makes the timing effect of a study larger in the year the property is placed in service.
Property acquired after September 27, 2017 and before January 20, 2025 stays under the earlier phase-down. Written binding contracts signed before that cutoff can keep later-closed property in the older schedule. Notice 2026-11 is interim guidance on those dates.
Buildings themselves are not bonus-eligible. The 27.5- and 39-year recovery periods exceed the 20-year ceiling in §168(k). The study’s timing effect comes from the shorter-lived components it identifies, not from changing the building’s statutory life.
How the classes are chosen
Section 168 maps class lives to recovery periods and assigns statutory lives to residential rental property, nonresidential real property, and qualified improvement property. Rev. Proc. 87-56, reproduced in Appendix B of Publication 946, supplies most class lives. Whether a particular fixture is personal property or a structural component is decided under Treas. Reg. §1.48-1 and the cases that apply it.
Industry examiner matrices in Publication 5653 illustrate how those tests have been applied in retail, restaurants, residential rentals, and a few other settings. Each matrix says it reflects that industry’s general facts. Do not treat a matrix row as an automatic class for every building.
What the audit guide is — and is not
Publication 5653 is written for IRS examiners. The guide states that it is not an official pronouncement of the law or the position of the Service and cannot be used, cited, or relied upon as such. It is current only through its February 2025 revision, which predates Public Law 119-21.
The guide is still the most detailed public statement of what examiners look for: documentation, a site inspection, a legal explanation, and reconciliation to actual cost. It does not create an “IRS-approved” study format, and no study should be described that way.
Sources
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- 5IRS Publication 5653 — Cost Segregation Audit Techniques Guide (rev. 2-2025)(opens in a new tab)
Written for IRS examiners. The guide states it is not an official pronouncement of law and cannot be cited as authority. It predates the July 2025 law.
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- 7IRS Publication 946 — How To Depreciate Property (2025)(opens in a new tab)
Appendix B reproduces the Rev. Proc. 87-56 class lives.