By Daniel Sabet · CFO & Financial Advisor, GreenGrowth CPAs · Real Estate & Tax Strategy · Los Angeles, CA | Published August 2026 | Tax Advisory
A cost segregation study is worth dramatically more in 2026 than anyone projected two years ago, and most property owners have not adjusted. Under the old schedule, bonus depreciation was falling to 20% this year and disappearing in 2027. The One Big Beautiful Bill Act reversed that. It made 100% bonus depreciation permanent for qualified property acquired and placed in service on or after January 19, 2025. So the components a study reclassifies now deduct in full, in year one, with no sunset to plan around.
QUICK ANSWER
A cost segregation study breaks a building into components and assigns each one its real depreciable life. A commercial building otherwise depreciates over 39 years, or 27.5 for residential rental. Carpet, specialty electrical, cabinetry, parking surfaces and landscaping have lives of 5, 7 or 15 years. Those shorter-life components qualify for bonus depreciation, now permanently at 100%. The effect is timing rather than a larger total deduction. It also works retroactively on buildings you already own, without amending prior returns.
Cost Segregation Study: At a Glance
What Property Owners Should Know First
- The math changed in your favor: Bonus depreciation was scheduled to fall to 20% in 2026 and vanish in 2027. OBBBA made 100% permanent for property acquired and placed in service on or after January 19, 2025.
- A building is not one asset: It is a structure plus everything inside and around it, and those components have much shorter real lives.
- It is timing, not magic: You take the same total deduction. You just take it now, and cash today is worth more than cash in year thirty.
- It works retroactively: A building bought years ago without a study can catch up missed depreciation in a single year, using Form 3115 rather than amended returns.
- Recapture is the real limit: Selling soon claws back much of the benefit, since reclassified components recapture at ordinary rates rather than the 25% rate.
- Passive loss rules can trap it: A large deduction helps only if you have income it can offset, so passive activity rules decide whether the benefit lands this year or waits.
- GreenGrowth’s role: We model the study against your actual position before you commission one. Book a cost segregation review →
How a Cost Segregation Study Actually Works
Without a cost segregation study, the default treatment is simple. The whole purchase price, less land, depreciates over 39 years. Residential rental runs 27.5 years. Straight line, no judgment required.
That treatment is convenient and it does not reflect reality. A building is a structure plus a great deal that is not structural. Carpet does not last 39 years. Neither does cabinetry, decorative lighting, or the wiring feeding a piece of equipment. The parking lot outside is not part of the building at all.
A cost segregation study identifies those components, assigns cost to each, then depreciates them on their real schedule instead of burying them in the 39-year figure.
What Moves Into Shorter Lives
▶ Typical Reclassification by Recovery Period
| Life | What Typically Lands There | Bonus Eligible? |
|---|---|---|
| 5-year | Carpet, decorative lighting, specialty electrical serving equipment, removable partitions, certain finishes | Yes |
| 7-year | Certain furniture, fixtures and equipment tied to the operation rather than the structure | Yes |
| 15-year | Land improvements: parking surfaces, sidewalks, landscaping, fencing, site utilities, exterior lighting | Yes |
| 15-year QIP | Qualified improvement property, meaning interior improvements to nonresidential buildings | Yes |
| 39 or 27.5-year | The structure itself: foundation, framing, roof, exterior walls | No |
Land itself never depreciates. Roofs and HVAC on nonresidential buildings are not bonus eligible, though they may qualify for Section 179 expensing where the building was already in service.
💬 The Conversation Worth Having
Owners usually ask us how much a cost segregation study will produce. That is the wrong first question, because the deduction is the easy part. The harder question is whether you can use it. A study that generates a large passive loss for someone with no passive income has not saved anything this year, it has created a carryforward. Meanwhile the same study for an owner with a real estate professional election, or with other passive income to offset, converts straight into cash. So run the usability test before you commission the study, not after.
Own commercial property and never had a study done? Twenty minutes tells you whether it applies.
Why a Cost Segregation Study Is Worth More Now
The value of a cost segregation study depends heavily on bonus depreciation, and that number moved twice in short order.
Under the previous schedule, bonus was set at 60% for 2024, 40% for 2025, 20% for 2026, then nothing from 2027. Investors were watching the window close. The One Big Beautiful Bill Act, signed in July 2025, removed the phase-down entirely. It made 100% bonus depreciation permanent for qualified property acquired and placed in service on or after January 19, 2025.
The practical difference is large. A component moved into a 5-year life would have generated a 20% first-year deduction under the old 2026 rate. It now generates 100%. So the same cost segregation study produces a far bigger first-year number than most owners were projecting.
Two Dates That Decide Eligibility
IRS guidance confirms that both the acquisition date and the placed-in-service date must fall on or after January 19, 2025. Property under a written binding contract entered into before January 20, 2025 is generally treated as acquired on that contract date. That can push otherwise eligible property back under the old phase-down.
So check your contract date rather than your closing date. Owners who signed in late 2024 and closed in 2025 sometimes assume they qualify when they do not.
A Cost Segregation Study Works on Buildings You Already Own
This is the part most owners do not know, and it is often the largest opportunity sitting in a portfolio.
You do not have to run a cost segregation study in the year you buy. A building purchased, built or renovated years ago can still be studied. The depreciation you should have taken but did not gets caught up in a single year, through a change in accounting method filed on Form 3115 with a section 481(a) adjustment.
No amended returns are required, which surprises people. The catch-up lands on the current return as one deduction rather than being spread backward across closed years.
For an owner holding a property bought years ago and depreciating it as one 39-year asset, that catch-up can be substantial.
Where a Cost Segregation Study Does Not Work
Most articles on this topic stop at the upside. Three situations turn a cost segregation study into wasted money, and any honest advisor raises them first.
You are selling soon. Accelerated depreciation reduces basis, so a sale triggers recapture. Worse, the reclassified components generally recapture at ordinary income rates rather than the 25% rate applied to building depreciation. A short hold can leave you worse off than doing nothing.
You cannot use the loss. Rental activity is generally passive, and passive losses offset passive income. Without passive income, a real estate professional election, or another route, the deduction becomes a carryforward rather than cash. That may still be worth having. It is a different proposition from the one most marketing implies.
The property is too small. A quality engineering-based study costs real money. Below roughly a million dollars in depreciable basis the fee starts eating the benefit. That threshold moves with property type and component mix.
One More Consideration for Multi-State Owners
Not every state conforms to federal bonus depreciation. California does not, so a California owner may take a large federal deduction and a much smaller state one. Separate depreciation schedules then have to be maintained. Model the state position alongside the federal one rather than assuming they match.
What Separates a Defensible Study From a Cheap One
The IRS publishes an audit techniques guide for this area, which tells you it examines these positions. A cost segregation study is a tax position, and it has to hold up.
Engineering-based, not rule of thumb. A defensible cost segregation study works from construction documents, invoices and a site inspection. A percentage applied to purchase price is not a study, whatever the report calls itself.
Component-level documentation. Each reclassified item needs its cost basis explained and its life justified. That documentation is the whole defense if anyone asks.
Someone who stands behind it. Ask whether the provider supports the study under examination, and at what cost. A firm that disappears after delivering a PDF has transferred the risk to you.
How GreenGrowth CPAs Approaches a Cost Segregation Study
We start where most providers finish. Before anyone commissions a cost segregation study, we model whether you can actually use the deduction, given your passive income position, hold period and state.
That conversation sometimes ends with us saying not yet. An owner planning to sell in two years, or one with no income to offset, is usually better served waiting. Nobody selling studies volunteers that.
When a Cost Segregation Study Makes Sense
Where the numbers work, we coordinate the study and handle the Form 3115 filing for retroactive catch-up. We then integrate the result into your wider tax planning rather than treating it as a standalone event. You can see the practice on our tax planning and compliance page.
KEY TAKEAWAYS
- ›OBBBA made 100% bonus depreciation permanent for qualified property acquired and placed in service on or after January 19, 2025. The old schedule had bonus falling to 20% in 2026 and disappearing in 2027.
- ›A building depreciates over 39 years, or 27.5 for residential rental. Components with 5, 7 and 15-year lives all qualify for bonus depreciation once a study identifies them.
- ›Check the contract date, not the closing date. A written binding contract entered before January 20, 2025 is generally treated as the acquisition date and can push property back under the old phase-down.
- ›It works retroactively. A building bought years ago can catch up missed depreciation in one year through Form 3115, with no amended returns needed.
- ›Three things break the case. Selling soon, because reclassified components recapture at ordinary rates. Passive loss limits, if you have no income to offset. And a property too small to carry the fee.
- ›Not every state conforms to federal bonus depreciation. California does not, so a large federal deduction can come with a much smaller state one and separate schedules to maintain.
Cost Segregation Questions Answered
The Basics
What is a cost segregation study?+
It breaks a building into its components and assigns each one its real depreciable life. A commercial building otherwise depreciates over 39 years, or 27.5 for residential rental. Carpet, specialty electrical, cabinetry, parking surfaces and landscaping have 5, 7 or 15-year lives instead, and those shorter-life components qualify for bonus depreciation.
Does a cost segregation study increase my total deduction?+
No. You take the same total deduction over the life of the asset. What changes is timing, and timing carries real value. Cash you keep now can be reinvested or used to pay down debt, while the same deduction spread across thirty years is worth considerably less in present value terms.
How does bonus depreciation affect a cost segregation study in 2026?+
It makes the study considerably more valuable than earlier projections suggested. Bonus was scheduled to fall to 20% in 2026 and disappear in 2027. The One Big Beautiful Bill Act made 100% bonus depreciation permanent for qualified property acquired and placed in service on or after January 19, 2025, so reclassified components can now deduct in full in year one.
Timing and Older Properties
Can I do a study on a building I bought years ago?+
Yes, and this is often the largest opportunity in a portfolio. Depreciation you should have taken but did not gets caught up in a single year through a change in accounting method, filed on Form 3115 with a section 481(a) adjustment. No amended returns are required, and the catch-up lands on the current return as one deduction.
Which date determines whether I get 100% bonus depreciation?+
Both the acquisition date and the placed-in-service date must fall on or after January 19, 2025. Property under a written binding contract entered into before January 20, 2025 is generally treated as acquired on that contract date. So check your contract date rather than your closing date, because signing in late 2024 and closing in 2025 can push property back under the old phase-down.
How large does a property need to be?+
A quality engineering-based study costs real money, so below roughly a million dollars in depreciable basis the fee starts eating the benefit. That threshold moves with property type and component mix. A property heavy on land improvements can justify a study at a lower value than a plain warehouse would.
Risks and Limits
What happens to the benefit when I sell?+
Accelerated depreciation reduces your basis, so a sale triggers recapture. The components a study reclassifies generally recapture at ordinary income rates rather than the 25% rate applied to building depreciation. A short hold period can therefore leave you worse off than taking no study at all, which is why hold period should be settled before commissioning one.
What if I have no income to offset the deduction?+
Rental activity is generally passive, and passive losses offset passive income. Without passive income, a real estate professional election, or another route, the deduction becomes a carryforward rather than immediate cash. That can still be worth having, and it is a different proposition from what most marketing implies. Test usability before commissioning the study.
Does my state follow federal bonus depreciation?+
Not every state does. California, for example, does not conform, so an owner can take a large federal deduction alongside a much smaller state one and then maintain separate depreciation schedules. Model the state position alongside the federal one rather than assuming they match.
Choosing a Provider
What makes a cost segregation study defensible?+
Three things. An engineering-based approach working from construction documents, invoices and a site inspection rather than a percentage applied to purchase price. Component-level documentation explaining each item’s cost basis and life. And a provider who supports the study under examination. The IRS publishes an audit techniques guide for this area, which tells you it examines these positions.
How does GreenGrowth CPAs handle cost segregation?+
We model whether you can actually use the deduction before anyone commissions a study, testing your passive income position, hold period and state conformity. Sometimes that conversation ends with us recommending you wait. Where the numbers work we coordinate the study, handle the Form 3115 filing for retroactive catch-up, and integrate the result into wider tax planning.
The Deduction Is the Easy Part. Using It Is the Question.
Book a cost segregation review. We test whether the deduction lands as cash this year or becomes a carryforward, before you spend anything on a study.
GreenGrowth CPAs · Tax Advisory Team
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