Cost Segregation Study: The Complete Guide for Real Estate Investors (2026)

A cost segregation study splits the purchase price of a building into its parts, so that the parts that wear out faster can be depreciated faster. This guide covers what a study does, who benefits, what changed in 2025, how the IRS looks at studies, and what can go wrong. It links out to deeper articles for each topic.

This is general education, not tax advice. Your CPA should confirm how these rules apply to your return.

What a cost segregation study does

When you buy a rental property, you normally depreciate the building as one asset:

• 27.5 years for residential rental property
• 39 years for nonresidential real property (office, retail, warehouse)

Both use straight-line depreciation. The IRS Cost Segregation Audit Techniques Guide describes the building itself as "section 1250 property" and notes that equipment, furniture and fixtures are "section 1245 property" with shorter recovery periods, such as 5 or 7 years. A study identifies the parts of your purchase that belong in the shorter categories and assigns each a cost.

Typical reclassified items:

• 5 and 7-year property: appliances, carpeting, specialty lighting, removable fixtures, certain cabinetry, and equipment that serves the business rather than the structure
• 15-year property: land improvements such as parking lots, sidewalks, fencing, landscaping and outdoor lighting
• 27.5 or 39-year property: the structure itself, which stays on the long schedule

Land is never depreciable. A study does not change that. For how much typically moves between categories, see cost segregation reclassification percentages by property type.

Why it matters more now: 100% bonus depreciation

Property with a recovery period of 20 years or less can qualify for bonus depreciation, which lets you deduct the cost in the first year instead of spreading it out. That covers the 5, 7 and 15-year assets a study creates. It does not cover the building structure.

The One, Big, Beautiful Bill made 100% bonus depreciation permanent for qualifying property acquired after January 19, 2025. The IRS confirmed this in Notice 2026-11, issued January 14, 2026. You can read the IRS announcement directly.

Two cautions:

• The date that counts is the acquisition date, which is generally tied to when a binding written contract was signed. If you contracted to buy before January 20, 2025, a different bonus percentage may apply. Ask your CPA.
• Bonus depreciation for used property has conditions, including that you did not previously use the property. A study does not change your eligibility, it only sizes the assets.

If an older article tells you bonus depreciation falls to 20% in 2026, it is out of date. See bonus depreciation in 2026.

A worked example

Say you buy a rental house for $500,000 and the land is worth $100,000. The building basis is $400,000.

Without a study: $400,000 over 27.5 years is about $14,500 of depreciation per year. With a study that moves 25% of the building ($100,000) into 5, 7 and 15-year property, with 100% bonus depreciation:

• $100,000 deducted in year one
• The remaining $300,000 over 27.5 years is about $10,900 per year
• Year-one depreciation is about $110,900

That is roughly $96,400 more in year-one deductions. At a 24% federal bracket that is about $23,100 of tax effect, and at 37% about $35,700. These figures ignore the mid-month convention, state tax and the limits below. The total depreciation over time is the same. You are moving deductions earlier. Try your own numbers in the ROOM42 calculator.

The limits that decide whether you can use the deduction

A bigger deduction only helps if you can use it. Check these before you order a study.

Passive activity rules. Rental losses are generally passive. They offset passive income, and may be limited against your wages. A $25,000 special allowance exists for some active participants, but it phases out between $100,000 and $150,000 of modified adjusted gross income. Unused losses carry forward. Real estate professional status. If you meet the IRS tests, including more than 750 hours a year in real property trades or businesses and more than half of your personal services in them, and you materially participate in the rental, losses are not treated as passive. This is a facts-heavy test and a common audit issue. Short-term rentals. If the average guest stay is 7 days or less, the activity is not treated as a rental activity under the passive loss regulations, so material participation tests apply instead. That is why some Airbnb owners can use cost segregation losses against other income. See cost segregation for short-term rentals. At-risk and basis limits. You can only deduct losses up to your basis and at-risk amount.

Depreciation recapture when you sell

Cost segregation does not erase tax, it defers it. When you sell:

• Gain on the 5, 7 and 15-year property is "recaptured" as ordinary income, up to the depreciation you took.
• Gain on the building from straight-line depreciation is "unrecaptured section 1250 gain," taxed at a maximum 25% federal rate.

Holding the property, a 1031 exchange, or holding until death can change the outcome, but those are planning decisions for your CPA. Read depreciation recapture on rental property before you decide.

Already own the property? The look-back study

You do not need to amend old returns. If you bought or built a property in a prior year and never did a study, you can generally do one now and claim the missed depreciation in the current year by filing Form 3115, Application for Change in Accounting Method. The catch-up amount is called a section 481(a) adjustment. Details are in look-back cost segregation studies.

What makes a study hold up in an audit

The IRS published Publication 5653, the Cost Segregation Audit Techniques Guide, to train its examiners. It lists the study methods the IRS prefers. The detailed engineering approach, using actual cost records, and the detailed cost estimate approach both rank high. Studies built on rules of thumb with little documentation tend to draw more questions. The guide also notes there is no bright-line test for sorting section 1245 from section 1250 property, so each item depends on facts.

A defensible study usually has:

• A clear description of the property and the date placed in service
• An itemized list of assets with a cost and a recovery period for each
• A stated method for how costs were assigned
• Photos or documentation of the items claimed
• A qualified preparer who can explain the study if asked

You can read the IRS audit techniques guide yourself. For a comparison of doing it yourself versus using a professional, see DIY vs professional cost segregation.

When a study is not worth it

Skip or delay a study if:

• Your building basis is small, so the tax effect would not cover the cost
• You expect to sell within a short time and recapture would reduce the benefit
• Your losses would be suspended under the passive rules with no income to use them against
• You are in a very low bracket now and expect a much higher one later

Is cost segregation worth it? walks through these cases with numbers.

What a study costs

Traditional engineering firms commonly quote thousands of dollars per property. ROOM42 charges a one-time $525 per unit. See cost segregation study cost for what drives the range, and the pricing page for ROOM42 details.

Steps to get started

Gather your closing statement and a list of improvements.

Confirm with your CPA that you can use the deduction (passive rules, status, bracket).

Run a quick estimate in the calculator.

Order the study and give your CPA the report.

Your CPA claims the depreciation, or files Form 3115 if the property was placed in service in a prior year.