Cost Segregation · Brief · Working level
When to commission a cost segregation study
The best time is the placed-in-service year, but look-back studies via Form 3115 catch up missed depreciation in one year without amending. Renovations reset the question; an imminent sale usually ends it. A decision table.
The best year to commission a cost segregation study is the year the building is placed in service; the second-best year is any year the owner still expects to hold the property for several more. What actually drives the timing decision is not the study itself — providers can analyze a 15-year-old building as easily as a new one — but the tax mechanics around it: bonus depreciation eligibility, the Form 3115 catch-up, and recapture waiting at the exit.
Placed-in-service year: the clean case
Segregating basis before the first return is filed means every component starts in its correct class — 5-, 15-, 27.5- or 39-year — with no method change and full bonus depreciation on qualifying classes (100% for property acquired after January 19, 2025). Depreciation reporting runs through Form 4562 as usual. For a large acquisition, engage the study when the deal closes, not in the following March; the engineering work needs closing statements, appraisals, and site access.
Look-back studies: the one-year catch-up
An owner who has depreciated everything at 27.5 or 39 years has not lost anything permanently. A look-back study with Form 3115 treats the reclassification as an automatic accounting method change: the entire shortfall between depreciation claimed and depreciation allowable arrives as a negative Section 481(a) adjustment, deducted in full in the year of change. No amended returns, no reopened statutes. A building placed in service in 2019 and studied in 2026 can produce six years of missed accelerated depreciation in one line. The method-change framework is described in Pub 538.
Renovation and expansion triggers
Major capital work reopens the analysis twice over. The new spend should be segregated as it is placed in service — much renovation work lands in 5- and 15-year classes or as qualified improvement property. And the demolition side supports partial disposition elections: writing off the remaining basis of components torn out, which requires knowing what those components were worth. A renovation without component-level records forfeits that deduction permanently, since the partial disposition election must be made for the year of the disposition.
The pre-sale no-go zone
Five-year property is Section 1245 property, and its accelerated depreciation recaptures as ordinary income at sale. A study commissioned 18 months before closing accelerates deductions that flip straight back into ordinary income — a short-lived timing benefit that fees and rate mismatch can turn negative. The exceptions, and what a study can still do for an exit (allocation support, 1031 planning, partial dispositions), are covered in recapture planning before a sale.
Decision table
When a study does and does not make sense, by situation:
| Situation | Study? | Mechanism |
|---|---|---|
| Acquiring or constructing now, holding 5+ years | Yes — now | Placed-in-service classification, bonus |
| Owned 2–15 years, straight-line to date, holding | Yes | Look-back, Form 3115, §481(a) catch-up |
| Major renovation underway | Yes | Segregate new spend; partial dispositions on removals |
| Sale expected within ~2 years, no 1031 planned | Generally no | Benefit converts to §1245 recapture |
| Sale into a planned 1031 exchange | Maybe | Deferral continues; model both sides |
| Passive owner with no usable losses | Defer | Losses suspend under §469; study when they can be used |
Frequently asked questions
- When is the best time to do a cost segregation study?
- The year the property is placed in service. Assets start in the correct MACRS classes on the first return, bonus depreciation applies immediately, and no accounting method change is needed. The second-best time is a look-back study using Form 3115, which claims all missed depreciation as a one-year Section 481(a) adjustment without amending prior returns.
- Can I do a cost segregation study on a building I bought years ago?
- Yes. A look-back study reclassifies the components, and Form 3115 — an automatic accounting method change — brings the entire difference between depreciation claimed and depreciation allowable into the current year as a negative Section 481(a) adjustment. No amended returns are filed, and properties placed in service a decade or more ago remain eligible.
- Should I do a cost segregation study before selling a property?
- Usually not. Accelerated deductions taken shortly before sale largely convert into Section 1245 ordinary-income recapture at closing, shrinking the benefit to a brief timing difference — sometimes a net loss after fees. The main exceptions are a planned 1031 exchange or a study needed to support partial disposition and allocation positions, which is exit planning rather than acceleration.