🇺🇸 Made in America·100% U.S.-Based Team · 24+ Years in Cost Segregation
If you own the building your business operates out of, you can usually use cost segregation to move a meaningful slice of that building out of the 39-year depreciation bucket and into 5-year and 15-year buckets. Under current federal law, property in those shorter buckets that was acquired and placed in service after January 19, 2025 can be eligible for 100 percent bonus depreciation. That means the deduction can land in the first tax year you own and use the building, instead of trickling out over almost four decades.
Owner-occupied buildings are one of the cleanest places to use this strategy for one simple reason: you are using the building in your own business, so the deduction is not trapped behind the passive activity rules the way it is for many landlords. The catch is that the way you hold the building (personally, through an LLC, or through your operating company) changes how well the deduction works. Get that part right and the strategy is powerful. Get it wrong and you can end up with a large deduction you cannot use this year.
You run a business and you also own the walls around it: the contractor who bought the shop where her crews report every morning, the distributor who purchased the warehouse he used to lease, the professional practice that bought its office building, the owner who occupies part of a building and leases the rest. If you are a pure landlord with no business of your own in the building, start with what cost segregation is and come back to this one when you buy your own shop.
June Whitfield is an illustration, built to explain the idea. She runs a mechanical contracting company in Peoria, Illinois with about thirty employees. For eleven years she leased a cramped shop and office from a landlord who raised the rent every other year. In January 2026 she finally bought a building of her own for $2,000,000 and moved her crews in the same month. It has a shop floor, a two-story office wing, a fenced yard for trucks, and a paved lot. She holds it in a single-member LLC that leases it to her S corporation, and her CPA groups the rental with the business as one activity under Reg. 1.469-4(d)(1)(ii), a choice the structure section below explains.
Her CPA did what most CPAs do by default. The land was separated out, and the remaining building cost went onto a 39-year straight-line schedule. It was correct, and it left a large amount of money sitting in the future. June's business had a strong year, her tax bill was higher than she wanted, and she had just written a very big check for the down payment. The building she had just bought was full of components the tax code treats differently from the structure itself. She did not know it because nobody had asked.
When you buy or build a commercial building, the tax code starts with a default: the whole thing is nonresidential real property with a 39-year recovery period. The IRS has never said everything inside and around a building belongs in that bucket. Over decades of Tax Court decisions and IRS guidance, a framework developed for sorting the parts of a property into the correct recovery periods. Cost segregation is the fully engineered and accounted process of applying that framework to your specific building. The result separates your property into groups:
A shop floor adds its own wrinkles, such as process equipment and machinery that may belong in a shorter class life. Which items land where depends on the facts of your building and on the tests the courts have set out. For the legal framework, read our breakdown of the Whiteco six-factor test and the court decision in Hospital Corporation of America v. Commissioner (109 T.C. 21, 1997). Dollars moved into the 5-year and 15-year classes can be eligible for bonus depreciation. Dollars left in the 39-year class cannot.
Bonus depreciation is the engine. Under the law enacted in 2025, 100 percent bonus depreciation was restored for qualifying property acquired and placed in service after January 19, 2025. For a deeper look, see our guide to 100 percent bonus depreciation under the One Big Beautiful Bill Act. Two practical points for owner-occupants:
Rental property comes with a major obstacle: the passive activity loss rules. Losses from rental activities generally can only offset passive income, unless you qualify under an exception such as real estate professional status. That is why we spend so much time on material participation and real estate professional status for landlords.
When you use the building in your own active business, the depreciation on it is a business expense. It reduces the income of the business that uses the space. There is no need to qualify as a real estate professional, and there is no passive limitation sitting between you and the deduction. That only works as cleanly as it sounds when the building and the business are tied together in the right way, which brings us to structure.
Many business owners hold their building in a separate LLC for liability protection and have that LLC lease the property to the operating company. That is a sensible setup, and it creates a tax wrinkle. When a property is rented to a business the owner materially participates in, the self-rental rule applies: net income from that rental is treated as nonpassive, while a net loss from it stays passive unless the business and the building are in the same activity or grouped under Reg. 1.469-4(d)(1)(ii). So if your cost segregation deduction pushes the building entity into a loss, that loss may be suspended instead of flowing through to offset your operating business income. We cover this in why a cost segregation loss gets stuck in a self-rental. The summary for owner-occupants:
Here is the planning order in practice. Russell Tran and his brother own 50 percent each of both a regional supply company and the LLC that holds its $3,000,000 warehouse. Before ordering a study, their CPA asked what happens to the deduction inside the LLC, saw that a large first-year deduction would turn the LLC's modest rental profit into a passive loss, and checked whether the brothers qualified to group the rental with the operating business, which depends on facts like identical ownership in both. None of that changed the engineering. The order is facts, then structure, then study, then return.
Every building is different, so we do not hand out component dollar tables or a one-size-fits-all percentage. Our team does a component-by-component analysis of construction documents, closing statements, invoices, plans, and related records, under the first two approaches the IRS Audit Techniques Guide describes: engineering from actual cost records, or engineering with documented estimates reconciled to actual cost. The product is a component schedule your CPA imports and an examiner can trace line by line, signed by credentialed professionals, and defended for as long as you own the building. The estimated study hands your CPA a percentage and nothing underneath it. Our summary of the 13 elements of a quality study in the IRS Cost Segregation Audit Techniques Guide lists what your CPA and any future examiner will expect to see.
In an owner-occupied commercial building, the categories that tend to deserve attention are interior finishes and fixtures such as carpet, specialty lighting, and decorative fixtures; data, telecom, security, and access control systems; dedicated electrical and plumbing that serve specific equipment or processes; site work such as paved parking and truck areas, sidewalks, fencing, landscaping, and exterior lighting; and business-specific build-out that exists because of what your company does inside the building. The share of a building's cost that moves into shorter-life classes typically falls between 20 percent and 35 percent, which is $200,000 to $450,000 in additional first-year federal deductions per $1 million of depreciable basis. Your building will land somewhere in that range, and the engineering decides where.
Back to June. These figures are illustrative. She buys her building for $2,000,000. A land allocation of 20 percent ($400,000) is assumed, which leaves a depreciable basis of $1,600,000. (Land is never depreciable, and how land is valued matters, as our post on land value allocation explains.) The building is placed in service in January 2026, and the IRS mid-month table rate for a January placed-in-service date on 39-year property is 2.461 percent. An engineered study reclassifies 25 percent of the depreciable basis into 5-year and 15-year property.
| Item | Without a study | With a study |
|---|---|---|
| Purchase price | $2,000,000 | $2,000,000 |
| Land (not depreciable) | $400,000 | $400,000 |
| Depreciable basis | $1,600,000 | $1,600,000 |
| Reclassified to 5-year and 15-year property (25%) | $0 | $400,000 |
| Left in 39-year property | $1,600,000 | $1,200,000 |
| Bonus depreciation at 100% | $0 | $400,000 |
| First-year 39-year depreciation (January table rate, 2.461%) | $39,376 | $29,532 |
| Total first-year depreciation | $39,376 | $429,532 |
The difference in first-year depreciation is $390,156. At a 37 percent federal rate, that is about $144,400 of federal tax June does not pay this year. June files jointly, and her company earns more than the deduction, so the depreciation offsets business income and the excess business loss limit of Section 461(l) does not come into play. If it did, the cap on her 2026 return would be $512,000 joint ($256,000 single), adjusted annually.
Depreciation is a timing benefit. The $400,000 June deducts in year one is depreciation she would have taken anyway, over 39 years, and she is taking it sooner. The $1,200,000 left in the 39-year bucket still depreciates at roughly $30,800 per year after the first year. The value comes from having the deduction now, when it can offset current income.
Section 179 expensing stops at your business income. Bonus depreciation keeps going, which means the deduction can be taken even in a year when it creates a loss. A business loss that exceeds your income can generally be carried forward as a net operating loss, limited to a percentage of taxable income in the year it is used. For noncorporate taxpayers, Section 461(l) caps how much net business loss can offset other income in a given year, with the excess carried forward; our guide to the excess business loss limit and cost segregation covers how it works. A study also leaves you choices: your CPA can model how much bonus depreciation fits your income this year, and in some cases elect out of bonus depreciation for a class of property. The classification comes from the engineering. What you do with the deduction comes from your tax strategy.
Section 179 is a different tool: it expenses certain qualifying property and certain improvements to nonresidential buildings, but it has dollar limits and is capped by the taxable income of the business. We compare all three in our guide to how owners use Section 179, bonus depreciation and cost segregation together.
You bought the building three, five, or ten years ago. Did you miss your chance? Not necessarily. The IRS allows a taxpayer who has been using an incorrect depreciation method to correct it by filing an application for a change in accounting method (Form 3115). When a study is done on a building you already own, the depreciation you did not take in earlier years can generally be claimed in the current year as a catch-up adjustment under Section 481(a), with no need to amend prior returns. Cost Seg America prepares the Section 481(a) computation and, for a separate fee, the Form 3115 itself. Your CPA files it with the return. Our guide to catching up missed depreciation without amending returns goes deep on this.
The deadline for a study that supports your current-year return is the day you file that return, extensions included. December 31 passing does not close the window.
Faster depreciation means a lower tax basis in the building, and when you sell, some of the depreciation you took is taxed differently from regular long-term capital gain. Depreciation taken on shorter-life personal property (the 5-year class) can be recaptured as ordinary income. Depreciation on the building portion is taxed at a maximum federal rate of 25 percent as unrecaptured Section 1250 gain. Our plain-English walkthrough of what you actually pay back in recapture after cost segregation shows the numbers.
For many owner-occupants this is less of a concern than it sounds, because they hold the building for decades, pass it down, or exchange into another property. For an owner who expects to sell within a few years, it can change the answer.
A study needs at least $180,000 of depreciable basis after land; below that, the fee eats the benefit. If a sale is coming within a couple of years, ordinary-income recapture on the 5-year property arrives almost as fast as the deduction, and the time value is small. If the building sits in a leasing entity that cannot group with the business, the loss is passive and may sit suspended until there is passive income or a sale, and paying for a study to move a number from one carryforward to another is a poor trade. And if the business is in a loss year already, a bigger loss runs into the net operating loss and Section 461(l) limits instead of producing a refund. Our article on when a cost segregation study does not pay lays out those cases, and we would rather tell you that up front than sell you a study that does not fit.
Yes. For an owner-occupied building, the depreciation generally offsets the income of the business that uses the space, subject to how the property is held and your own tax situation.
Not for an owner-occupied building used in your own active business. Real estate professional status matters for rental activity, where the passive activity rules limit the use of losses. If you also own rentals, those rules still apply to them.
It depends. The self-rental rule can cause a net loss in the leasing entity to be treated as passive. A grouping election or a structural change may help, and your CPA needs to evaluate it with the actual facts, before the study.
Often, yes. A lookback study lets you claim previously unclaimed depreciation in the current year through a change in accounting method, filed by your CPA on Form 3115, without amending prior returns.
No one can promise what the IRS selects for examination. A study that follows the IRS Cost Segregation Audit Techniques Guide and is supported by documentation is a sound, recognized method. You can read more in our guide to the five audit triggers an examiner looks for first.
Your CPA files Form 3115 with your tax return. Our team prepares the study, the Section 481(a) computation, and, for a separate fee, the Form 3115 itself, and we work alongside your CPA so the numbers match what the return needs.
If you own a commercial building you operate out of, or you are about to buy one, send Jim Dougherty and his team at Cost Seg America your closing statement and a few photos. You will have a free proposal within 24 hours, with the likely reclassification and the first-year number, and we will bring your CPA into the conversation on structure before anything is ordered. Call 1-888-365-5023 or email info@costsegamerica.com. You will get straight answers, including when the answer is that a study is not right for you.
This article is educational and general in nature and does not constitute tax, legal, or accounting advice; tax law changes and every owner's facts differ, so confirm your situation with your CPA before making any decision.
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