Business owners who occupy their own commercial buildings often depreciate the whole building over 39 years. A cost segregation study can move a meaningful share of that cost into shorter recovery periods. Here is how the numbers can work.

Hypothetical example: A chiropractor buys an office building with a $5,000,000 depreciable basis (excluding land value). Without cost segregation, the building depreciates over 39 years, about $128,000 a year. Office buildings typically reclassify 28% to 41% of depreciable basis into 5-, 7- and 15-year property. At the 28% baseline, that's $1,400,000. If the building was acquired and placed in service after January 19, 2025, 100% bonus depreciation lets that full amount be deducted in year one, plus about $92,000 on the remaining $3,600,000 of 39-year property.

That's about $1.49 million of first-year depreciation instead of about $128,000, or roughly $1.36 million of additional deductions. At a 24% marginal rate, that's about $327,000 of federal tax, if the deduction can be used that year. Figures use a full year of straight-line depreciation for simplicity.

Two limits apply. If the building is held in a separate entity that leases it to the practice, the self-rental rules can affect how the losses are treated. And business losses that offset other income are subject to the excess business loss limit.

When to Run the Study

When should you conduct a cost segregation study? The answer depends on your plans for the property. If you're purchasing a building with the intention of performing a gut renovation, wait until the renovation is complete. Just be sure to document the construction process thoroughly with photos and detailed cost tracking.

If you're buying a property to place in service immediately, with only minor renovations planned over time, the study is usually best run right after closing. This timing allows you to benefit from partial asset disposition when you eventually replace components. You'll be able to take additional expense deductions when you remove and replace those assets.

The key is adapting your cost segregation timing to match your business strategy for the property. There's no one-size-fits-all approach here.

Components That Are Often Missed

Some of the larger reclassifications come from what's called "functional allocation." Electrical and plumbing distribution can be split by what they serve. When a circuit is dedicated to specific equipment, such as an X-ray unit, the outlet, the wiring and the share of the distribution system that feeds it can be classified as personal property with a shorter recovery period, often five years. General-purpose outlets and wiring stay with the building.

Two identical outlets can be classified differently based on their use. Removable flooring can also be shorter-life property. The distinction between site improvements and equipment, and between equipment attached to the building and freestanding equipment, affects your cost segregation study results.

Recent Tax Law Changes and Their Impact

Bonus depreciation is a major driver of first-year results. The scheduled phase-down is over: under the One Big Beautiful Bill, 100% bonus depreciation is now permanent for qualifying property acquired and placed in service after January 19, 2025. A $100,000 five-year asset placed in service under those rules generates the full $100,000 as a first-year deduction, rather than the $52,000 it would produce at the 40% rate that applies in 2025 to property acquired on or before January 19, 2025 (20% in 2026).

Interior improvements you make to a nonresidential building after it is placed in service are generally qualified improvement property (QIP): 15-year property, eligible for bonus depreciation since the CARES Act fix. QIP excludes enlargements, elevators, escalators and the building's internal structural framework. Separately, Section 179 can expense QIP, along with roofs, HVAC, fire protection and alarm systems, and security systems added to nonresidential property after it is placed in service, subject to the Section 179 limits.

Selecting the Right Cost Segregation Professional

When evaluating cost segregation providers, prioritize firms that employ engineering expertise. The preferred methodologies involve detailed engineering with either actual or estimated costs. Ask potential providers how they determine national cost averages. They should reference industry standards like Marshall and Swift or RS Means.

Verify that the professionals conducting your study have engineering backgrounds. Ask about their track record. Have they completed hundreds or thousands of studies? Have they worked across various asset classes and geographical regions? Their methodology should explicitly include detailed engineering approaches.

Documentation and Long-Term Strategy

The most important support if the IRS examines your study is documentation that ties back to the basis used in the study. Whether for renovations, acquisitions, or new construction, this connection matters most. If you're claiming real estate professional status or material participation, tracking those hours is equally important.

Beyond immediate tax benefits, develop an exit strategy. Schedule a call with a R.E. Cost Seg expert to discuss your options. Whether you're planning a 1031 exchange or what some call a "lazy 1031" (buying another property in the same year and cost segregating it to offset the recapture income), thinking ahead is crucial. A 1031 exchange can defer some or all of the recapture, but it now covers real property only, and Section 1245 recapture can still apply.

Plan for recapture. If you bought a property for $1 million, took $500,000 in depreciation, and later sold it for $2 million, that depreciation comes back as taxable income. Depreciation on 5- and 7-year components is recaptured as ordinary income to the extent of gain; straight-line depreciation on the building is taxed at up to 25%. Even if you didn't take the depreciation you were entitled to, your basis is still reduced by the depreciation you could have taken. A 1031 exchange can defer recapture, and heirs who inherit the property receive a stepped-up basis. An exit plan can reduce or defer the recapture tax.

Cost segregation works best as part of your broader tax and business planning, with your CPA modeling the deductions, the loss limits and the exit. Use our free commercial property depreciation calculator to estimate first-year depreciation on your building.