Cost Segregation: When Accelerating Depreciation Is Worth the Study

A cost segregation study on a $2 million apartment building can reclassify $400,000 to $500,000 of that basis from 27.5-year property into 5-, 7-, and 15-year buckets. With 100% bonus depreciation restored, most of that reclassified basis comes off in year one instead of trickling out over decades. On a $500,000 reclassification at a 37% marginal rate, that is meaningful cash, but the study itself costs $5,000 to $15,000, and the strategy quietly backfires for a specific set of owners. Here is how to tell which side of the line you are on.

What is a cost segregation study, and what does it actually do?

A cost segregation study is an engineering-based analysis that breaks a building's purchase or construction cost into its component parts and reassigns each to its correct MACRS recovery period. Instead of depreciating the whole thing as real property, you separate out the pieces that qualify as shorter-lived property.

Under §168, residential rental real property depreciates over 27.5 years and nonresidential over 39 years, both straight-line. But a building is not one asset. Carpeting, cabinetry, decorative lighting, specialty electrical, and dedicated equipment wiring are often 5- or 7-year personal property. Land improvements (parking lots, sidewalks, landscaping, fencing) are 15-year property. The IRS's own Cost Segregation Audit Techniques Guide endorses the methodology when it rests on a defensible engineering approach, tracing back to the Hospital Corporation of America Tax Court decision (109 T.C. 21, 1997) that established component classification.

The 5-, 7-, and 15-year buckets matter because they are eligible for bonus depreciation under §168(k), and the shorter straight-line schedules front-load deductions even without bonus.

How much does cost segregation actually save?

The benefit is a timing shift, not free money: you are pulling deductions forward, not creating new ones. On a typical study, 20% to 40% of a building's depreciable basis gets reclassified into shorter-lived property.

Run the pattern I see most often on a $2 million commercial building (say $1.6 million of depreciable basis after backing out land):

• Without a study: $1.6M / 39 years ≈ $41,000 per year.
• With a study reclassifying 30% ($480,000) to 5- and 15-year property, and applying 100% bonus depreciation to the eligible portion, first-year depreciation can exceed $500,000: the full $480,000 of reclassified basis plus straight-line on the remaining building.

The cash value of that acceleration is the extra deduction times your marginal rate, adjusted for the time value of money. At a 37% federal rate plus state, moving roughly $450,000 of deductions from future years into year one is worth about $166,500 federal in nominal tax deferral, and because a dollar deducted today beats a dollar deducted in 2040, the real economic gain is the discounted spread.

The critical word is deferral. Accelerated depreciation lowers your basis faster, which means a larger gain, and depreciation recapture, when you sell.

Where does bonus depreciation stand now, and why does timing matter?

Bonus depreciation under §168(k) is back at 100%. The Tax Cuts and Jobs Act set 100% bonus for property placed in service through 2022, then began a scheduled phase-down (80% for 2023, 60% for 2024) that was headed to zero by 2027. The One Big Beautiful Bill Act, enacted in July 2025, ended the phase-down: 100% bonus depreciation is restored permanently for qualified property acquired after January 19, 2025.

The acquisition date is now the hinge. Property acquired on or before January 19, 2025 remains subject to the phase-down percentage for its placed-in-service year, so confirm which regime your purchase falls under before you model anything. For new acquisitions, the entire reclassified amount in the 5-, 7-, and 15-year buckets can come off in year one, which makes the study math considerably more favorable than it was during the phase-down years.

When is a cost segregation study worth the cost?

A study makes sense when the reclassified deductions produce a tax benefit that clearly exceeds the study fee and survives a realistic holding period and recapture analysis. In practice, that points to a few conditions:

1. Basis of roughly $500,000 or more. Below that, the reclassified amount often does not generate enough acceleration to clear a $5,000–$15,000 fee with margin. Some firms offer scaled-down studies for smaller properties, but scrutinize the fee-to-benefit ratio.
2. A high marginal rate. The benefit scales directly with your bracket. At 37% the math is compelling; at 12% it rarely is.
3. A holding period long enough that recapture doesn't erase the deferral, or a plan to defer that gain (see the §1031 caveat below).
4. Current taxable income to absorb the deductions, or a passive-loss profile that lets you use them.

Here is where studies go to waste: owners commission one, generate a large paper loss, and then discover the loss is trapped by the passive activity rules of §469. Rental losses are passive by default. Unless you qualify as a real estate professional under §469(c)(7) or the property is nonpassive to you for another reason, those accelerated deductions may just pile up as suspended losses, deferring the deferral and blunting the whole point.

When does cost segregation backfire?

It backfires when you accelerate deductions you can't use, or when recapture at sale costs more than the deferral was worth. Watch for these:

• Short holding period. If you plan to sell in two or three years, you are trading a modest deferral for a recapture bill. §1245 recapture on the personal-property portion is taxed at ordinary rates, and §1250 unrecaptured gain on real property is capped at 25%. Front-loading depreciation loads up the §1245 exposure.
• Trapped passive losses. As above: if §469 suspends the loss, you paid for a study to create a deduction you can't currently deduct.
• A §1031 exchange that doesn't clear recapture. A like-kind exchange under §1031 can defer the gain, but the accelerated personal property complicates the exchange and, post-TCJA, personal property no longer qualifies for §1031 treatment at all: only real property does. That reclassified 5-year property is now non-like-kind.
• State nonconformity. Many states decouple from federal bonus depreciation. Your federal benefit may be far larger than your combined federal-plus-state benefit, and you'll track separate depreciation schedules for years.

Can you do a cost segregation study on a building you've owned for years?

Yes. You do not have to amend prior returns. You file a Form 3115, Application for Change in Accounting Method, and take a §481(a) adjustment to "catch up" all the depreciation you should have claimed in a single year.

This is one of the most underused moves I see. An owner who has held a property for six years can commission a study today, file Form 3115 as an automatic change under the applicable Revenue Procedure, and deduct the entire cumulative catch-up in the current year. No amended returns, no six years of 1040-X filings. The catch-up can be a large deduction in one shot, which raises the same passive-loss and income-absorption questions above, so model the §481(a) adjustment against your actual return before filing.

Who should run the study, and what should the report contain?

Use a provider that produces an engineering-based study consistent with the IRS Cost Segregation Audit Techniques Guide, not a "rule of thumb" allocation that won't survive exam. A defensible report documents the methodology, the source of costs, photographs, and the specific asset classifications with their MACRS lives.

A weak study is worse than no study: it hands an examiner an easy adjustment and can trigger recapture on reclassifications that don't hold up. This is a facts-and-circumstances area, and the right answer depends on your entity, your income, your state, and your exit plan. Walk the numbers through with your tax advisor, and consult your attorney on anything touching a planned sale or exchange.

Sources

• IRC §168: MACRS recovery periods (27.5-year residential, 39-year nonresidential)
• IRC §168(k): bonus depreciation (100% restored by the One Big Beautiful Bill Act for qualified property acquired after January 19, 2025)
• IRC §469 and §469(c)(7): passive activity loss rules and real estate professional exception
• IRC §1245: recapture on personal property (ordinary rates)
• IRC §1250: unrecaptured §1250 gain (25% cap)
• IRC §1031: like-kind exchanges (real property only, post-TCJA)
• IRC §481(a): adjustment on change in accounting method
• IRS Form 3115: Application for Change in Accounting Method
• IRS Cost Segregation Audit Techniques Guide
• Hospital Corporation of America v. Commissioner, 109 T.C. 21 (1997)