Cost segregation study for a small rental or apartment building: what it is and when it pays

What a cost segregation study does

When you buy an apartment building, you split the price between land, which is not depreciated, and the building, which is. Without a study, the building is generally depreciated straight line over 27.5 years as residential rental property. A study looks closer. Some parts are tangible personal property, such as appliances and carpeting, which are 5 year property for a residential rental activity. Some are land improvements, such as fences, paving and landscaping, which are 15 year property. The rest stays 27.5 year building.

The IRS describes the idea in its Cost Segregation Audit Technique Guide (Publication 5653, revised February 6, 2025). The guide says the incentive is the shorter recovery periods and accelerated depreciation methods, including bonus depreciation, and notes that a building is generally residential rental property with a 27.5 year recovery period that uses straight line depreciation. It also says there is no general bright-line test for sorting building parts from personal property, so the study is a matter of facts and engineering judgment.

The depreciation classes themselves are in Publication 527, which lists residential rental property at 27.5 years and puts appliances, carpeting and furniture used in a residential rental activity in the 5 year class.

How a study works and who does it

The IRS guide lists several approaches, from a detailed engineering approach using actual cost records to cost estimates, a residual estimation approach and rule of thumb methods. It states that the IRS does not require one particular approach, and a quality study is supported by documentation and prepared by people competent in construction, estimating and the tax rules. A typical process: a firm reviews your closing documents and plans, inspects the building, sorts the costs by class, and gives you a report you attach to your tax work.

• Gather: closing statement, purchase price allocation, any appraisal, renovation invoices.
• Site visit and review of building systems and finishes.
• A report that assigns each part to a class with the reasoning.
• Your tax preparer uses the report on Form 4562 and your return.

A worked example

Example a made-up buyer pays $1,000,000 for a small apartment building. The allocation is $200,000 land and $800,000 building. Without a study, the building is depreciated at $800,000 / 27.5 = about $29,091 a year (ignoring the first year's partial-year rule).

Example a study finds $120,000 of 5 year property (appliances, carpet, some fixtures) and $60,000 of 15 year land improvements (paving, fencing, landscaping), leaving $620,000 as 27.5 year building. The 27.5 year part is $620,000 / 27.5 = about $22,545 a year. In year one, with the regular method and no bonus, 5 year property takes 20% ($24,000) and 15 year property takes 5% ($3,000), per the tables in Publication 946, so first year depreciation is about $24,000 + $3,000 + $22,545 = $49,545, versus $29,091 without a study, about $20,454 more.

Example if 100% bonus depreciation applies to the $180,000 of 5 and 15 year property (see bonus depreciation on rental property), year one becomes $180,000 + $22,545 = $202,545, about $173,454 more than $29,091. The total over the life is the same; it arrives earlier. All figures are an illustration and your tax preparer applies the real rules.

When it pays, and when it does not

• Size. The study has a fee, so the larger the depreciable basis, the better the odds. Ask for a written fee quote and an estimate of the reclassified amount before you commit. Do not assume the saving.
• Whether you can use the deduction. A bigger deduction can create a rental loss. Under the passive activity rules, losses from rentals are generally limited to passive income, with a special allowance of up to $25,000 for some owners who actively participate that phases out as income rises, as explained in Publication 925. Unused losses carry forward, so a study can push deductions into later years instead of saving tax now.
• How long you will hold. Depreciation you take can be taxed again when you sell. Personal property you depreciated is treated differently from the building on a sale, and the IRS guide discusses sections 1245 and 1250 property for that reason. Ask your tax preparer to model a sale before you decide.
• State rules. Some states do not follow the federal rules for bonus depreciation. Check yours.
• Newer or heavily renovated buildings are usually better candidates than old ones with little recent spending, because there is more cost to sort.

Can you do it after you already filed?

Yes, in many cases. The IRS guide says a change in depreciation method or recovery period that results from reclassifying property is generally a change in accounting method, made by filing Form 3115 and taking the catch-up as a section 481(a) adjustment, rather than by amending earlier returns. That is a job for your tax preparer, and it is covered further in what to do if you forgot to depreciate.

How DoorKeeping handles it

DoorKeeping does not perform cost segregation studies or give tax advice. What it does is keep the records a study needs and a preparer will ask for: each property's own books, the purchase price and closing costs on the building, improvements kept apart from repairs, and expense accounts mapped to Schedule E lines. You can ask your AI app for a property's books and hand your tax preparer or the study firm the figures.

Sources

1. IRS, Cost Segregation Audit Technique Guide, Publication 5653 (revised 2-6-2025), read Oct 30, 2026
2. IRS, Publication 527, Residential Rental Property, read Oct 30, 2026
3. IRS, Publication 946, How To Depreciate Property, read Oct 30, 2026
4. IRS, Publication 925, Passive Activity and At-Risk Rules, read Oct 30, 2026

Questions

What is a cost segregation study?

An engineering and tax analysis that sorts a building's cost into land, land improvements, personal property and building, so that parts with shorter lives are depreciated faster.

Does cost segregation give me more total depreciation?

No. The total depreciation over the life is the same. A study moves deductions into earlier years.

Is cost segregation worth it for a small rental?

It depends on the building's cost, the fee, whether you can use the extra deductions now and how long you hold the property. Get a written fee quote and an estimate before deciding, and ask your tax preparer.