Cost Segregation Studies: Faster Depreciation for Buildings Under IRC §168
In Short
Cost Segregation is an engineering-based study that splits the cost of a building into parts that can be depreciated over shorter periods than the building itself. It is commonly used by owners of commercial and rental real estate who want larger depreciation deductions in the first years of ownership.
TL;DR
- Residential rental buildings are generally depreciated over 27.5 years and nonresidential buildings over 39 years, but some parts of a property qualify for 5-, 7- or 15-year lives [1][3].
- Shorter-lived parts may also qualify for bonus depreciation, which the One Big Beautiful Bill Act made a permanent 100% for qualified property acquired after January 19, 2025 [4].
- The IRS publishes an Audit Techniques Guide describing what a quality study looks like [2].
- Faster deductions can be recaptured as ordinary income when the property is sold, and passive loss rules can limit their use [5][6].
Quick Facts
| Legal Reference | IRC §168 |
|---|---|
| Complexity | High |
| Audit Risk | Medium |
| Setup Cost | Moderate to high — a professional engineering-based study |
| Time to Implement | Several weeks for the study; applied on the return for the year placed in service or by an accounting method change |
| Illustrative Example | Illustrative example, not a projection. An investor buys a $2,000,000 commercial building (not counting land). Without a study, the building is depreciated over 39 years, about $51,000 a year. A study assigns $400,000 to 5-, 7- and 15-year property. If that property qualifies for 100% bonus depreciation, the first-year deduction is far larger, but the building's later yearly deductions are smaller and part of the gain on a sale may be taxed as ordinary income. Actual results depend on the facts, the study and the tax rates involved. |
Key Numbers & Limits
| Item | Limit or Rule | Notes |
|---|---|---|
| Residential Rental Building | 27.5-year recovery period | [1][3] |
| Nonresidential Real Property | 39-year recovery period | [1] |
| Personal Property and Land Improvements | Commonly 5, 7 or 15 years | Depends on the asset class [1][2]. |
| Bonus Depreciation | 100% for qualified property acquired after January 19, 2025 | Permanent under P.L. 119-21; a 40% (60% for certain property) election is available for the first tax year ending after that date [4]. |
| Recapture on Sale | §1245 gain taxed as ordinary income; unrecaptured §1250 gain taxed at up to 25% | [5] |
What Is Cost Segregation?
Cost segregation is the process of identifying the parts of a building's cost that are personal property or land improvements rather than the building itself, so they can be depreciated over shorter periods under IRC §168 [1][2]. Without a study, the whole cost of a residential rental building is generally depreciated over 27.5 years and a nonresidential building over 39 years [1][3].
Examples of items that may qualify for shorter lives include certain electrical and plumbing serving specific equipment, carpeting, cabinetry, decorative lighting, parking lots, sidewalks and landscaping. Whether an item qualifies depends on how it is used and on the asset classes the IRS applies, which the IRS discusses in its Cost Segregation Audit Techniques Guide [2].
The IRS guide says a quality study is accurate and well documented, and it describes several methods, from a detailed engineering approach based on actual cost records to rule-of-thumb estimates. It treats detailed engineering approaches as the most reliable [2].
Shorter-lived property can also qualify for bonus depreciation under IRC §168(k). The One Big Beautiful Bill Act (Public Law 119-21) made bonus depreciation a permanent 100% for qualified property acquired after January 19, 2025, and the IRS issued interim guidance in Notice 2026-11 [4].
How Does Cost Segregation Work?
- An owner buys, builds or renovates a building used in a business or held for rent [1].
- A specialist — often an engineer working with a tax professional — reviews plans, cost records and the site and assigns costs to asset classes with their recovery periods [2].
- The owner depreciates each class over its own recovery period, and may claim bonus depreciation on qualified property [1][4].
- For a building already in service, the owner may apply a study to past years by filing an accounting method change rather than amending returns [2].
- Losses created by the deductions are subject to the passive activity rules for owners who do not qualify for an exception [6].
- On a sale, depreciation taken on §1245 property is generally recaptured as ordinary income, and straight-line depreciation on the building is taxed as unrecaptured §1250 gain at a maximum 25% rate [5].
The Good: What Are the Benefits of Cost Segregation?
- Moves depreciation into earlier years, which can lower taxable income in the first years of ownership [1][2].
- With 100% bonus depreciation restored for property acquired after January 19, 2025, qualifying short-lived property can be deducted in the year it is placed in service [4].
- Can be applied to buildings bought in earlier years through an accounting method change [2].
- Supports clearer records of building components, which helps when parts are later replaced or disposed of [2].
The Bad: What Are the Drawbacks of Cost Segregation?
- A quality engineering-based study costs money, which may not pay off for smaller properties [2].
- Total depreciation over the life of the property does not change; the study only changes timing.
- Faster depreciation reduces basis, so more gain is taxed when the property is sold, and some of it is taxed as ordinary income [5].
- Rental losses are usually passive, so owners who are not real estate professionals and do not meet another exception may not be able to use the losses against wages or business income [6].
- State income tax rules for depreciation can differ from the federal rules.
The Ugly: What Are the Serious Risks of Cost Segregation?
- Studies that use unsupported estimates or assign building components to short lives without a basis can be adjusted on audit, with additional tax, interest and a 20% accuracy-related penalty on the resulting underpayment [2][7].
- Large deductions in early years can create a large tax bill on sale, when the recapture is due all at once [5].
- Promoters who sell aggressive studies alongside social-media claims of wiping out wage income fit the IRS's warnings about misleading tax advice on social media [8].
Who Uses Cost Segregation?
Who It's Commonly Used By
- Owners of commercial buildings, warehouses, hotels, apartments and medical or retail properties [2].
- Investors who bought, built or substantially renovated a building in recent years.
- Real estate professionals and short-term rental owners whose losses are not limited by the passive activity rules [6].
Who It's Generally Not Suited For
What Are the Key Rules & Requirements for Cost Segregation?
- Residential rental property is generally depreciated over 27.5 years and nonresidential real property over 39 years [1][3].
- Property that is personal property or a land improvement can have a 5-, 7- or 15-year recovery period [1][2].
- Qualified property acquired after January 19, 2025 is eligible for 100% bonus depreciation, with an election to use a lower percentage for the first tax year ending after that date [4].
- A study applied to a building already in service is generally reported as a change in accounting method [2].
- Depreciation on §1245 property is recaptured as ordinary income on sale [5].
- Rental real estate losses are generally passive unless an exception applies, such as real estate professional status [6].
What Are Common Mistakes & Red Flags With Cost Segregation?
- A rule-of-thumb percentage applied to the purchase price with no site visit or cost records [2].
- A preparer who cannot show credentials or explain the method used [2].
- Allocating structural components, such as walls or roofs, to short-lived classes.
- Ignoring the land value, which is never depreciable.
- Claiming the losses against wages without qualifying for a passive loss exception [6].
- Not planning for recapture tax when the property is sold [5].
Frequently Asked Questions
Is Cost Segregation Legal?
Yes. Cost segregation applies the depreciation rules of IRC §168 to each part of a property, and the IRS publishes an Audit Techniques Guide describing how examiners review studies [1][2]. The question on audit is whether the study is accurate and well documented.
Does Cost Segregation Work With Bonus Depreciation in 2025 and 2026?
Yes, for qualified property. The One Big Beautiful Bill Act made a permanent 100% bonus depreciation deduction available for qualified property acquired after January 19, 2025 [4]. Buildings themselves are not bonus-eligible; the shorter-lived parts identified in a study may be.
Can a Cost Segregation Study Be Done on a Building Bought Years Ago?
Yes. The IRS guide notes that a study for property already in service is commonly applied through an accounting method change, which lets the owner catch up missed depreciation without amending prior returns [2].
What Happens to Cost Segregation Deductions When the Property Is Sold?
Depreciation reduces basis, which increases gain on sale. Depreciation on §1245 property is generally taxed as ordinary income, and straight-line depreciation on the building is taxed as unrecaptured §1250 gain at a maximum 25% rate [5].
Sources
- 26 U.S. Code §168 — Accelerated Cost Recovery System — Legal Information Institute, Cornell Law School
- Publication 5653, Cost Segregation Audit Techniques Guide — Internal Revenue Service
- Publication 527 (2025), Residential Rental Property — Internal Revenue Service
- Treasury, IRS Issue Guidance on the Additional First Year Depreciation Deduction Amended as Part of the One Big Beautiful Bill — Internal Revenue Service
- Publication 544, Sales and Other Dispositions of Assets — Internal Revenue Service
- Publication 925, Passive Activity and At-Risk Rules — Internal Revenue Service
- 26 U.S. Code §6662 — Imposition of Accuracy-Related Penalty on Underpayments — Legal Information Institute, Cornell Law School
- Dirty Dozen Tax Scams for 2026 — Internal Revenue Service
Primary sources only: the Internal Revenue Code, Treasury regulations and official agency guidance. Read how Zentavos researches these reports.