Bonus depreciation and cost segregation are separate things, and you only need the second to unlock the first inside a purchased building. IRC section 168(k) applies to any qualified asset with a recovery period of 20 years or less. If you bought a $4,000 refrigerator for a rental and have the receipt, you can take bonus depreciation on it with no study at all. The study becomes necessary when the short-life assets are buried inside a single purchase price.
Why a building purchase is different
When a fund pays $1,200,000 for a short-term rental, the closing statement shows one number. Nothing on it says how much of that price is carpet, cabinetry, a paved driveway, or landscaping. To depreciate those pieces over 5 or 15 years and claim bonus on them, you must allocate basis to each asset class, and the allocation has to survive examination. The IRS Cost Segregation Audit Techniques Guide describes the methods examiners look for, and the detailed engineering-based approach, built from cost data, site documentation, and construction knowledge, is the quality standard it describes most favorably. A guess scribbled on a spreadsheet is not an allocation an examiner will respect, and the depreciation rules in IRS Pub 946 put the burden of substantiating basis on the taxpayer.
What you can do without a study
- Take bonus on separately invoiced personal property: appliances, furniture, equipment
- Take bonus on new land improvements with their own contractor bills, like a $15,000 fence
- Take bonus on a renovation where the invoices themselves break out each component
In each case the paper trail already establishes cost, so no reallocation is needed.
A sensible order of operations
Start by checking whether a study is worth buying at all. Amadae's cost segregation screen, part of its savings playbook, models the likely reclassification and first-year benefit for a property. It is a screening estimate, explicitly not an engineering study, and it exists so you do not spend thousands on a study that cannot pay for itself. If the screen shows a strong benefit, Amadae coordinates with an engineering study firm, and when a look-back applies, Amadae prepares the Form 3115 with the section 481(a) catch-up and files the return that uses the study.
Worked example
A fund closes on a $1,200,000 beach rental in 2026 with $240,000 allocated to land. A screen suggests meaningful short-life content; the engineering study then documents $190,000 of 5-year and 15-year property. At the permanent 100% bonus rate under OBBBA for property acquired after January 19, 2025, that is a $190,000 first-year deduction that would have been unreachable without the allocation.
When you can skip it
If a property is small, mostly land value, or held inside a structure where losses would only suspend under IRC section 469, the study fee may outweigh the benefit. That is exactly the call the screen is built to make before any money is spent.