Cost segregation is an engineering-based tax study that reclassifies portions of a commercial property's cost from the standard 39-year depreciation schedule into shorter 5, 7, and 15-year asset classes. By moving qualifying components into faster recovery periods, an owner accelerates depreciation deductions into the early years of ownership and defers tax.
How Does Cost Segregation Work?
Cost segregation works by separating a building into its component assets, then assigning each to the shortest legally supportable Modified Accelerated Cost Recovery System (MACRS) recovery period. Rather than depreciating the entire structure over 39 years for commercial property, an engineer isolates items like carpeting, decorative lighting, parking lots, and landscaping that qualify for faster write-off.
The IRS permits this because different building components genuinely have different useful lives. Per Engineered Tax Services and Uncle Kam's 2026 cost segregation guide, engineers sort costs into 5-year personal property such as specialized electrical and carpeting, 7-year property such as built-in cabinetry, 15-year land improvements such as parking lots and sidewalks, and the 27.5 or 39-year structural shell that stays on the long schedule.
MACRS class | Example components |
5-year personal property | Carpeting, decorative fixtures, security systems, specialized wiring |
7-year personal property | Built-in cabinetry, process-related equipment |
15-year land improvements | Parking lots, sidewalks, landscaping, site lighting, fencing |
27.5 or 39-year structure | Foundation, roof, framing, load-bearing walls |
The reclassified dollars matter most when paired with bonus depreciation, which lets an owner deduct a large share of shorter-life assets in the first year rather than spreading them across the recovery period.
Why Cost Segregation Matters
Cost segregation matters because it converts a slow, decades-long deduction into a large near-term one, improving early cash flow and the time value of every tax dollar. Per multiple 2026 practitioner sources including Engineered Tax Services and Taxstra, a study typically reclassifies 20% to 40% of a commercial building's cost into shorter recovery periods.
That reclassification is powerful under current law. The One Big Beautiful Bill Act (OBBBA), signed July 4, 2025, permanently restored 100% bonus depreciation for qualifying property placed in service after January 19, 2025, per Cherry Bekaert and Boyer & Ritter. Every dollar a study moves into a 5, 7, or 15-year class can then be fully deducted in year one rather than amortized over decades.
The deferred tax is not free money. Accelerated deductions lower the property's tax basis, so a later sale can trigger depreciation recapture. Cost segregation is a timing strategy, not an elimination of tax, and its value is the return earned on cash freed up today.
Example
An investor buys a commercial property and allocates $5,000,000 of basis to the building, excluding land. Without a study, the annual deduction is $5,000,000 divided by 39 years, or roughly $128,205 per year. A cost segregation study reclassifies 30% of basis, $1,500,000, into 5, 7, and 15-year assets eligible for 100% bonus depreciation. The table follows the first-year comparison.
Line item | Without study | With study |
Building basis (excluding land) | $5,000,000 | $5,000,000 |
Reclassified to short-life assets (30%) | $0 | $1,500,000 |
Year-1 bonus depreciation on reclassified assets | $0 | $1,500,000 |
Remaining basis on 39-year schedule | $5,000,000 | $3,500,000 |
Year-1 straight-line depreciation (39-year) | $128,205 | $89,744 |
Total year-1 depreciation | $128,205 | $1,589,744 |
The study lifts the first-year deduction from $128,205 to $1,589,744, an increase of $1,461,539. At a 37% marginal rate, that additional deduction defers roughly $540,769 of tax into later years, using the rounded whole-dollar deduction figures shown. The investor redeploys that cash immediately instead of waiting decades to recover it through the standard schedule.
Variations and Edge Cases
Cost segregation is not identical across every deal: it varies with property type, whether the owner performs a look-back study on prior years, and how depreciation recapture is treated at sale. A study on a class A office tower isolates different components than one on a warehouse. The table separates the common variants.
Variant | Treatment |
Look-back study | Applied to property held for years; catch-up deduction taken via Form 3115 without amending returns |
Purchased property | Study allocates the acquisition price across component classes |
New construction | Component costs often available directly from contractor invoices |
Partial asset disposition | Retired components written off when replaced, avoiding double depreciation |
Recapture at sale | Accelerated deductions reduce basis and can be recaptured as ordinary income or 1250 gain |
The common mistake is running a study on a property the owner plans to sell within a year or two. Short holds can surface the deferred tax as recapture before the time value of the acceleration is fully earned.
Cost Segregation vs Bonus Depreciation
Cost segregation is often confused with bonus depreciation, but they are separate tools that work together. Cost segregation is the study that identifies and reclassifies which building components qualify for shorter recovery periods. Bonus depreciation is the tax provision that lets an owner deduct a large share of those short-life assets in the first year.
A study creates the eligible pool of short-life assets; bonus depreciation determines how fast that pool is deducted. Per Cherry Bekaert, OBBBA restored the bonus rate to 100% for qualifying property placed in service after January 19, 2025. Without a cost segregation study, most of a building's cost stays trapped on the 39-year schedule and never reaches the bonus rate.
Frequently Asked Questions
What percentage of a building can cost segregation reclassify?A cost segregation study typically reclassifies 20% to 40% of a commercial building's cost into shorter 5, 7, and 15-year recovery periods, per 2026 practitioner sources including Engineered Tax Services and Taxstra. The exact share depends on property type, since finishes, fixtures, and site improvements vary by asset class.
Does cost segregation eliminate taxes or just defer them?Cost segregation defers tax rather than eliminating it. Accelerating depreciation lowers the property's tax basis, so a later sale can trigger depreciation recapture. The strategy's value is the return an owner earns by redeploying the tax savings today instead of recovering them slowly over 39 years.
How does bonus depreciation affect a cost segregation study?Bonus depreciation lets an owner deduct a large share of the short-life assets a study identifies in the first year. The One Big Beautiful Bill Act restored 100% bonus depreciation for qualifying property placed in service after January 19, 2025, per Cherry Bekaert, which magnifies the year-one benefit of a study.
Related Terms
Capital Expenditures
Net Operating Income
Due Diligence
Internal Rate of Return
Replacement Reserves