Cost Segregation Study: What It Is and When It Pays

A cost segregation study is an engineering-based analysis that separates a building's cost into components with shorter tax lives — carpeting, cabinetry, dedicated electrical, parking, landscaping — instead of depreciating everything over 27.5 or 39 years. The reclassified components become 5-, 7-, or 15-year property eligible for bonus depreciation, front-loading deductions into the first years of ownership.

On this page

1. How does cost segregation work?
2. What does a study cost?
3. When does it pay?
4. Can it be done on a building bought years ago?
5. Worked example
6. Frequently asked questions
7. Related guides
8. Official sources
9. Next step

How does cost segregation work?

A building bought for US$2 million is, by default, US$2 million of 39-year property (less land). But a building is made of parts, and tax law treats some of them as personal property or land improvements with their own MACRS classes. A cost segregation study — performed by an engineer or a specialist firm using construction cost data, blueprints, and a site visit — allocates the total cost among:

Studies typically move 20 to 40 percent of a commercial building's cost (excluding land) into the shorter classes — more for restaurants, medical offices, manufacturing plants, and hotels with heavy interior finish and specialized systems; less for warehouses and shells. Because 5-, 7-, and 15-year property qualifies for bonus depreciation, the reclassified amount can be deducted in the year the building is placed in service.

What does a study cost?

Third-party engineering firms typically charge in the low-to-mid four figures for a small commercial property and five figures for large or complex ones, with price depending on the building's size, age, and available documentation. Some firms offer a free feasibility estimate showing the projected reclassification before engaging. The IRS's Cost Segregation Audit Techniques Guide describes what a defensible study contains — an engineering-based approach with documented methodology — and a study that is merely a percentage rule of thumb does not meet it.

When does it pay?

The benefit is time value: deductions taken now instead of over decades. It pays when the owner has income to absorb the accelerated deductions (or can use the loss under the passive activity and excess business loss rules), expects to hold the property long enough that the acceleration matters, and faces a marginal rate now at least as high as at sale. It pays less when:

• The property will be sold within a few years — the reclassified 5- and 7-year components are section 1245 property, and bonus on 15-year land improvements is recaptured to the extent it exceeds straight line, so most of the acceleration comes back as ordinary income rather than the 25 percent-capped rate that applies to building depreciation (the section 1245 vs 1250 guide). A short hold converts the acceleration into a rate arbitrage that runs against the owner.
• The owner is a passive investor whose rental losses are suspended under the passive activity rules — the deductions are deferred until passive income or disposition, which erodes the time value.
• The building is small — the study's cost is a larger share of a modest reclassification.

It pays most for owners who will hold long-term or until death (a stepped-up basis at death eliminates the recapture entirely), for real estate professionals who can use rental losses against other income, and in the year of a large gain elsewhere that the accelerated deductions can offset.

Can it be done on a building bought years ago?

Yes. A "look-back" study on a building already in service allows the owner to catch up all the depreciation that would have been claimed under the reclassification, in the current year, through an automatic accounting-method change (Form 3115) with a section 481(a) adjustment — no amended returns required. Buildings placed in service in prior years with no bonus depreciation available at the time still benefit from the shorter lives going forward and the catch-up.

Worked example

A dental group buys a US$1.8 million medical office building (US$300,000 land). Default treatment: US$1.5 million over 39 years — about US$38,500 a year. A cost segregation study reclassifies US$420,000 into 5- and 7-year property (cabinetry, dedicated plumbing and electrical for the operatories, finishes) and US$130,000 into 15-year land improvements (parking, landscaping). With 100 percent bonus depreciation on the US$550,000 reclassified, first-year depreciation is about US$574,000 (the bonus amount plus straight-line on the remaining US$950,000 of building) instead of US$38,500; the study cost US$7,000. The group's partners are active in the practice, so the deductions offset practice income. If they sell in year six, the US$420,000 of 5- and 7-year property is recaptured as ordinary income, along with roughly US$82,000 of the land-improvement bonus (its excess over straight line), and the remaining US$48,000 or so is unrecaptured section 1250 gain at up to 25 percent; if they hold for twenty-five years, the acceleration is worth a decade of deferred tax with the recapture far off and partly at lower rates.

Frequently asked questions

Official sources

Publication 946 states: “The recovery period of property is the number of years over which you recover its cost or other basis. It is determined based on the depreciation system (GDS or ADS) used.” — Internal Revenue Service, Publication 946, How To Depreciate Property, https://www.irs.gov/publications/p946

Publication 544 states: “A gain on the disposition of section 1245 property is treated as ordinary income to the extent of depreciation allowed or allowable on the property.” — Internal Revenue Service, Publication 544, Sales and Other Dispositions of Assets, https://www.irs.gov/publications/p544

Next step

Fairlight Accounting is a cross-border accounting and tax practice with a U.S. Tax Desk and a Canadian Tax Desk. Our U.S. Tax Desk handles cost segregation feasibility analysis, look-back studies with Form 3115 catch-up depreciation, passive-loss and recapture modeling, and coordination with the engineering firm. See pricing or book a call.