Home / What is cost segregation?

What is a cost segregation study? The plain-English 2026 guide

By SegWise Tax TeamCurrent through IRS Notice 2026-11

Short answer: a cost segregation study is an engineering-based tax analysis that separates a property's short-lived components — fixtures, equipment, specialty systems, land improvements — from the building shell, so each piece depreciates over 5, 7, or 15 years instead of 27.5 (residential) or 39 (commercial) years. The deductions land earlier, cash flow improves now, and under current law 100% bonus depreciation can write off qualifying reclassified components entirely in year one.

How it works, in one paragraph per step

1. The building gets taken apart on paper

The IRS treats a rental house as one 27.5-year asset and an office as one 39-year asset — a simplification, not a fact. Inside both are hundreds of components the tax code actually assigns shorter lives: carpets and vinyl (5), appliances and signage (5–7), plumbing and HVAC replacements (often 5 as land or building improvements), fencing, landscaping, site lighting, and parking lots (15), security systems and specialty electrical (5–7). A study identifies each one and values it from your closing statement, appraisal, and construction cost detail.

2. The basis gets reclassified

Typical modeled results, as a share of the depreciable basis (purchase price less land): apartment buildings commonly land around 26–38%, offices 28–41%, medical offices 27–42%, industrial 25–39%, short-term rentals around 25–35% depending on what furniture and fixtures come with the deal. These are modeling ranges — the study measures your actual building, which is why engineered studies routinely beat generic percentage rules of thumb.

3. MACRS does the math; current law makes it front-loaded

Each reclassified dollar moves onto a faster MACRS schedule. Since the One Big Beautiful Bill Act (P.L. 119-21, §70301) made 100% bonus depreciation permanent — for property both acquired and placed in service after January 19, 2025 (binding-contract date controls, per IRS Notice 2026-11) — a post-cutoff buyer can deduct 100% of the reclassified 5/7/15-year portion immediately. Contracts signed on or before that date follow the old phase-down (40% for 2025 in-service; 20% for 2026).

A worked example (modeled, not promised)

$600,000 duplex, contract signed Feb 2026	Without study	With SegWise study
Depreciable basis (less 18% land)	$492,000	$492,000
Reclassified to 5/15-year lives (modeled ~30%)	—	≈ $147,600
Year-one depreciation deduction	≈ $17,900	≈ $163,700 (100% bonus on reclassified + shell MACRS)
Year-one tax saved @ 24% marginal rate	≈ $4,300	≈ $35,000
SegWise fee (Full Engineered, modeled)	—	flat, quoted first (from $2,088)

Model uses our published 30% multifamily reclassification midpoint, mid-month convention, and IRS Table A-1 rates; individual results vary with basis, rate, and passive-activity treatment. Run your own numbers in the free calculator.

Do you need one? (And when you don't)

Rules of thumb we'll tell you even when they cost us a sale: a study usually pays when depreciable basis exceeds roughly $250K and you expect to hold several years; it rarely pays on a fixer about to be sold, a property in a 1031 pipeline with a fast resale, or when bonus/regular savings barely exceed the fee. Owned since 2018 or earlier? The Form 3115 catch-up is often the biggest single deduction available to you, claimed on this year's return with no amended returns.

“But will it trigger an audit?”

Cost segregation is IRS-recognized methodology — the framework examiners use is the agency's own Cost Segregation Audit Technique Guide (Pub 5653, updated February 2025). Examination risk follows documentation quality: engineering-based, photo-documented studies answer the questions examiners ask, while DIY percentage studies invite the questions you can't answer. Every SegWise study includes audit support at no additional charge.

What about depreciation recapture at sale?

Accelerated deductions are time-value money. Recapture on the residential/commercial shell is generally capped at 25% (unrecaptured §1250 gain); 5/7/15-year components recapture as ordinary income to the extent of depreciation taken. With 100% bonus now permanent for qualifying acquisitions, investors who hold past the first year and refinance or sell later commonly keep net savings many multiples of the eventual recapture — our studies include an exit-modeled view so you decide with both ends of the trade visible. (Depreciation reduces basis and can reduce sale gain — the recapture question is about character and timing, not a phantom.)

Sources & further reading

Ready to see your building's numbers?

Free calculator below, free written proposal with a flat fee one click away. Or start with the specific deep-dives:

Free calculator →How much does it cost? →Bonus depreciation 2026 rules →Catch-up / Form 3115 →Latest IRS updates →

More questions, answered

Answers verified against current IRS guidance. Anything missing? Ask us and we'll publish it.

What is a cost segregation study?

A cost segregation study is an engineering-based tax analysis that separates the short-lived components of a property — fixtures, equipment, specialty systems, site improvements — from the building itself, so each component depreciates over 5, 7, or 15 years instead of 27.5 or 39 years. The result is larger depreciation deductions in the earliest years of ownership and more cash flow today. The IRS recognizes the methodology in its Cost Segregation Audit Technique Guide (Pub 5653).

How much does a cost segregation study cost?

SegWise publishes starting prices — 10% below the published fees of the national rapid-delivery firms: SegWise Rapid from $855 (questionnaire study for small rentals), SegWise Quick™ from $1,499 (24-hour engineered delivery), and our Full Engineered Study from $2,088 for residential and $2,457+ for commercial properties. Final pricing depends on property size, type, and complexity, and you get a flat quote — typically the same business day — before any work begins. Industry-wide, engineering-based studies commonly run $3,000–$15,000+.

Is a cost segregation study worth it?

For most properties with at least $250K of depreciable basis, yes: first-year tax savings typically run many multiples of the study fee (our case examples range from 10× to 90×), and you can quantify it before you spend a dollar using our free calculator and free written proposal. If the math is thin for your property, we tell you — not every property justifies a study yet.

I bought my property years ago. Is it too late?

No. Studies can be done retroactively to the year you placed the property in service. Missed depreciation from prior years is claimed as a one-time "catch-up" deduction on your current return by filing Form 3115 — you do not amend prior-year returns. Most owners have been on the standard 27.5/39-year schedule, so the catch-up is often the single largest deduction they have ever claimed.

What is SegWise Quick™ and how is it finished in 24 hours?

Quick™ is our AI-accelerated study tier for deadline situations — closings, extensions, and year-end placed-in-service dates. AI pre-classifies components from your closing statement, blueprints, and invoices, then our engineers and CPAs review, correct, and sign the report — within 24 business hours of receiving complete property documents. Every Quick™ study carries the same IRS-defensible methodology and audit-ready documentation as our standard work.

Will cost segregation trigger an IRS audit?

Cost segregation is an IRS-recognized strategy used by millions of property owners, and audit rates follow the quality of the documentation, not the strategy itself. Studies that follow the engineering methodology outlined in the IRS Cost Segregation Audit Technique Guide carry materially less risk — and SegWise includes audit support with every study at no additional charge.

Find out what your building is hiding

Free proposal with your reclassification modeled — flat fee, same business day.

Get Free Proposal Try the free calculator