How to Do a Cost Segregation Study: Steps, Forms, and Payoff

A cost segregation study reclassifies parts of a building’s cost into shorter depreciation categories so you can deduct more of the purchase price sooner, and doing one involves five practical steps: gather your purchase and construction records, hire an engineering specialist to inspect the property, receive a report that assigns each component to a MACRS class, file the results on Form 4562 or Form 3115, and confirm the passive activity rules let you actually use the deduction. With 100% bonus depreciation restored permanently under the One Big Beautiful Bill Act, the payoff in 2026 is larger than it has been in years.¹

Step 1: Assemble Your Purchase and Construction Records

The engineering team cannot classify what you cannot document. Start with the closing statement. For mortgages originated after October 3, 2015, that’s the Closing Disclosure; for older transactions or reverse mortgages, it’s the HUD-1 Settlement Statement.² These forms verify the total purchase price and allocable closing costs, which together form your depreciable cost basis.

Next, separate land from building, because land cannot be depreciated.³ An appraisal report or the property tax assessment can support the split. The IRS accepts allocating cost based on the ratio of fair market values at the time of purchase, and if those aren’t available, the local tax authority’s assessed values work as a proxy.⁴

For newly constructed properties, pull the detailed construction invoices and contractor payment applications that break down materials and labor by trade. Blueprints and as-built drawings help the engineer verify quantities without relying solely on your accounting records. Better documentation lowers your fee, because the engineer spends less time on independent cost estimation.

Step 2: Understand How Components Get Classified

Knowing the classes the engineer will use lets you read the final report critically and spot anything missing. The Modified Accelerated Cost Recovery System (MACRS) groups property by recovery period. The building shell and its permanent structural components get the longest periods: 27.5 years for residential rental property and 39 years for nonresidential real property.⁵ The point of the exercise is to move components out of those slow buckets into faster ones.

Section 1245 personal property covers tangible items that aren’t part of the building structure: appliances, carpeting, furniture, decorative lighting, and specialized kitchen equipment. Residential rental items in this class typically fall into 5-year property, while office furniture and fixtures are 7-year property.⁶³
Land improvements are exterior elements like paved parking lots, fences, sidewalks, roads, and landscaping. These get a 15-year recovery period.⁷
Section 1250 property is the building itself and its structural components: walls, roofing, plumbing rough-ins, and the HVAC distribution serving the whole building. This stays on the long timeline.⁸

Qualified Improvement Property

If you’ve made interior improvements to a nonresidential building after it was first placed in service, those improvements can drop from the 39-year timeline to the 15-year class as qualified improvement property (QIP). The improvement cannot involve enlarging the building, adding an elevator or escalator, or modifying the building’s internal structural framework.³ QIP is also eligible for bonus depreciation, which is why tenant build-outs are often more tax-efficient than owners realize.

Step 3: Hire the Engineer and Complete the Site Inspection

The engineering phase is what separates a defensible study from guesswork. A specialist physically walks the property, photographing and measuring components that could qualify for a shorter period. They look for items a general accountant wouldn’t notice: dedicated electrical circuits serving specific equipment, removable wall coverings, HVAC systems that serve individual rooms like server closets or commercial kitchens, and site improvements separate from the building structure. The IRS Cost Segregation Audit Techniques Guide identifies engineering-based studies as the most reliable approach.⁹

After the walkthrough, the analyst assigns dollar values to each identified component, usually by calculating current replacement cost and adjusting back to the original construction or purchase year. Indirect costs like architect fees or permits get prorated across the various asset classes. The total of everything reclassified plus the remaining building shell must equal the total depreciable basis. The final report is a component-by-component breakdown with each item’s MACRS class and dollar value, formatted to feed directly into your tax return.

Step 4: File the Results on Form 4562 or Form 3115

How you report cost segregation results depends on timing. If the study is completed in the same year you placed the property in service, the reclassified assets go straight onto IRS Form 4562. You enter each asset category with its cost basis, the date placed in service, the recovery period, and the depreciation method.¹⁰ Assets eligible for bonus depreciation go on a separate line with the special allowance calculated at 100%.

Catching Up With Form 3115

More often, the study happens years after purchase. Reclassifying assets then requires a change in accounting method, reported on IRS Form 3115. This is how you capture all the depreciation you missed in prior years without amending old returns. The form calculates a Section 481(a) adjustment in Part IV representing the difference between what you actually deducted under straight-line and what you should have deducted under the shorter periods.¹¹ When that adjustment is negative, which is the typical cost segregation outcome, you take the entire catch-up deduction in a single tax year.

The filing mechanics matter. Attach the original Form 3115 to your timely filed federal return, including extensions. File a signed duplicate copy with the IRS National Office in Ogden, Utah (M/S 6111, Ogden, UT 84201), no earlier than the first day of the year of change and no later than the date you file the original return. Fax works instead of mail.¹¹ Cost segregation reclassifications qualify as automatic consent changes, so advance IRS approval isn’t required. You won’t receive an acceptance letter; the absence of a rejection means the change was processed as filed. Keep the certified mail receipt or fax confirmation.

Step 5: Confirm the Passive Activity Rules Let You Use the Loss

A cost segregation study can generate a large paper loss, but whether that loss actually reduces your tax bill this year depends on the passive activity rules. Rental real estate is generally treated as a passive activity, meaning losses can only offset other passive income unless an exception applies.¹² Many investors discover, too late, that the deduction they just accelerated is sitting in a suspended loss carryforward.

Two exceptions matter before you commission a study:

Active participation allowance. If you actively participate in managing a rental (approving tenants, making management decisions), you can deduct up to $25,000 of passive rental losses against non-passive income. That $25,000 phases out by 50 cents for every dollar of modified adjusted gross income above $100,000 and disappears entirely at $150,000.¹³
Real estate professional status. If you spend more than 750 hours per year in real property trades or businesses in which you materially participate, and those hours are more than half your total personal services across all businesses, rental losses are no longer automatically passive. This unlocks the full benefit of cost segregation.¹²

Suspended passive losses aren’t lost. They carry forward and become fully deductible when you dispose of the property in a taxable transaction. But if the goal is immediate cash flow, verify where you stand before spending money on the study.

What the Deduction Is Worth in 2026

The One Big Beautiful Bill Act restored 100% bonus depreciation and made it permanent by repealing the phase-down that had been reducing the percentage each year since 2023. For qualified property acquired after January 19, 2025, the full adjusted basis can be deducted in the first year the asset is placed in service.⁵ Bonus depreciation applies to MACRS property with a recovery period of 20 years or less, covering every 5-year, 7-year, and 15-year component the study identifies. Used property qualifies as long as you acquired it by purchase and didn’t previously use it yourself.¹

In practical terms, if the study reclassifies $400,000 of a commercial building’s basis into shorter-lived categories, you can potentially deduct the entire $400,000 in year one rather than spreading it across decades.

Cost of the Study and When It Pays Off

Professional engineering studies typically run $5,000 to $15,000 for standard commercial or residential rental properties. Fees can drop to about $3,000 for straightforward smaller properties and climb to $25,000 or more for complex industrial or medical facilities. Property size, building complexity, and the quality of construction records drive the range.

The IRS Cost Segregation Audit Techniques Guide warns against fee structures based on a percentage of identified tax savings, because they create an incentive to reclassify aggressively.⁹ A flat fee or hourly rate is safer. As a rough rule of thumb, the study should generate at least four to five times its cost in first-year tax savings. For a $1 million commercial property, a well-executed study commonly reclassifies 15% to 40% of the building’s cost into shorter-lived categories, which with 100% bonus depreciation can produce six-figure deductions in year one.

One Thing to Know Before You Start: Recapture at Sale

Accelerated depreciation is a deferral, not a permanent tax cut. When you sell, the IRS recaptures what you deducted. Section 1245 personal property (the 5-year and 7-year items) is recaptured at your ordinary income tax rate.⁶ Section 1250 property gets slightly better treatment: depreciation on the building and structural components is taxed as unrecaptured Section 1250 gain at a maximum rate of 25%.¹⁴

Recapture doesn’t erase the benefit, but it does reduce it. The value comes from the time gap: deducting a large sum today at your top marginal rate and paying recapture years later when you sell. Hold long enough and the present value of the savings exceeds the present value of the recapture. Sell through a 1031 like-kind exchange and recapture is deferred further into the replacement property.

1
Internal Revenue Service. Treasury, IRS Issue Guidance on the Additional First Year Depreciation Deduction Amended as Part of the One Big Beautiful Bill
2
Consumer Financial Protection Bureau. What Is a HUD-1 Settlement Statement?
3
Internal Revenue Service. Publication 946 (2024), How To Depreciate Property
4
Internal Revenue Service. Publication 527 (2025), Residential Rental Property – Section: Separating Cost of Land and Buildings
5
Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System
6
Office of the Law Revision Counsel. 26 USC 1245 – Gain From Dispositions of Certain Depreciable Property
7
Internal Revenue Service. Publication 527 (2025), Residential Rental Property
8
Office of the Law Revision Counsel. 26 USC 1250 – Gain From Dispositions of Certain Depreciable Realty
9
Internal Revenue Service. Cost Segregation Audit Techniques Guide
10
Internal Revenue Service. 2025 Instructions for Form 4562 – Depreciation and Amortization
11
Internal Revenue Service. Instructions for Form 3115 (Rev. December 2022)
12
Office of the Law Revision Counsel. 26 USC 469 – Passive Activity Losses and Credits Limited
13
Internal Revenue Service. Publication 925 (2025), Passive Activity and At-Risk Rules
14
Internal Revenue Service. Topic No. 409, Capital Gains and Losses