What a cost segregation study does
The tax code says a commercial building depreciates over 39 years and a residential rental over 27.5. But a building is not one asset. It is thousands of components, and many of them, things like specialty electrical, carpet and flooring, cabinetry, site paving, and landscaping, legally qualify for 5, 7, or 15-year depreciation instead.
A cost segregation study identifies those components, prices them, and documents them so your CPA can depreciate each one on its proper schedule. The deductions were always yours. The study moves them from someday to now, and a dollar of deduction today is worth far more than the same dollar in 2050.
What that looks like in practice. An investor buys a short-term rental for $1 million, with $800,000 allocated to the building after land. Because units rented on a transient basis are generally treated as nonresidential property rather than residential rental property, that building depreciates over 39 years, not 27.5. Suppose a study moves 18.5 percent of that building basis into five-year property and another 8 percent into 15-year land improvements, which is the middle of the range I have been seeing on short-term rental studies lately. With 100 percent bonus depreciation, that entire reclassified amount can generally be deducted in year one. At a 32 percent marginal rate, that is roughly $66,100 in real cash kept, not deferred indefinitely into future decades. The numbers are illustrative; your building, your allocation, and your tax situation set the actual result, which is exactly what the no-cost analysis estimates in advance.
Bonus depreciation is back at 100 percent, permanently
The One Big Beautiful Bill Act restored 100 percent bonus depreciation for qualified property acquired and placed in service after January 19, 2025, and made it permanent. That matters here because the property a study reclassifies into 5, 7, and 15-year lives is generally bonus-eligible. Cost segregation was worth doing when bonus was phasing down. At 100 percent, the first-year math gets dramatically better.
One nuance worth knowing. Property under a written binding contract signed before January 20, 2025 is treated under the old acquisition rules. If your purchase timeline is anywhere near that line, flag it early and we will confirm which regime applies before anyone spends money on a study.
There is more to this, including two elections buried in the IRS guidance and the reason bonus depreciation can never touch the building itself. I wrote it up separately in how bonus depreciation works.
Make sure the deduction lands somewhere you can use it
A study accelerates a deduction. Whether you can use that deduction this year is a separate question, and it is decided by the passive activity rules rather than by the study. Under section 469, rental activity is generally passive no matter how involved you are, and passive losses offset passive income rather than wages or business income.
Two ways out are well established, and both come down to how involved you are.
The first is qualifying as a real estate professional. The second applies to short-term rentals. If your average guest stay runs seven days or less, the property is not a rental activity in the first place, so the automatic passive rule never touches it.
Neither one works on its own. Both still require material participation, which the regulations define with seven specific tests.
Work this out before commissioning a study, not after. It is part of the no-cost analysis, and it occasionally changes the answer from yes to not yet.
Engineering-based is the only kind worth doing
Here is where I stand. An engineering-based study, with an in-person site visit by a trained professional, is the only kind of cost segregation worth paying for.
The market is full of cheaper options. Desktop studies. Software estimates. Rule-of-thumb shortcuts that never put a person inside your building. Every one of them hands you a number. What none of them hands you is documentation that stands up when the IRS asks how you got it.
The IRS publishes its own audit guide for cost segregation. It says plainly that two things decide whether a study survives an exam. How the work was done, and how well it was written up.
An engineering-based study is built from the construction documents, the real cost data, and a person walking the property. That is the standard I deliver, through CSSI, on every study, in every state.
Already owned the building for years? Even better.
You do not need to have bought the property recently. A lookback study catches up every dollar of depreciation you could have claimed since acquisition, and you take the entire catch-up in the current tax year through an automatic accounting method change on Form 3115. No amended returns, no reopening old years. For owners who have held property for five or ten years, the catch-up deduction is often the single largest line item on that year's return.
Who this fits, and who it does not
- Owners of commercial buildings, short-term rentals, long-term rentals, and multifamily properties
- Investors with enough income, or the right participation status, to use the deductions the study creates
- Recent buyers, new builders, renovators, and long-time owners with unclaimed depreciation
- Tax professionals who want a study partner whose documentation they can defend
And who it does not fit: owners planning to sell within a year or two, buildings with very low basis, and situations where passive loss rules would strand the deductions. Depreciation taken now is also subject to recapture rules at sale, which is a timing question your CPA and I should look at together before you commit. If the study will not pay for itself, I will tell you so at the analysis stage, before you spend a dollar.
Questions investors actually ask
What is a cost segregation study?
It is an engineering study that finds the parts of your building the tax code lets you write off over 5, 7, or 15 years instead of 27.5 or 39. The deductions show up while you still own the place, not decades from now.
How much of my building can be reclassified?
It depends on the property type. A meaningful share of building basis often qualifies, but the honest answer for your building comes from a property-specific analysis, not an average. That is what the no-cost analysis is for.
I bought my property years ago. Did I miss the window?
No. A lookback study with a Form 3115 method change lets you claim all the missed depreciation in the current year, without amending anything.
Will a study trigger an audit?
Cost segregation is an established, IRS-recognized practice with its own audit techniques guide. What draws trouble is thin documentation. An engineering-based study with a site visit exists precisely so that if questions come, the answers are already on paper.
What does a study cost, and is it worth it?
Fees depend on the property's size and complexity, which is why the process starts with a no-cost analysis projecting your estimated benefit before you commit. Here is my standing promise. If the projected savings will not clearly exceed the fee, I will tell you not to do the study.
Hear it explained
Start with the free number
One conversation. No documents to gather, no obligation, no pitch. You get an estimate of what a study would save on your specific property, and an honest answer if it is not worth doing.