1. How Cost Segregation Works

A standard property purchase is normally depreciated as one asset over a long, fixed schedule. A cost segregation study breaks the purchase price into its component parts — carpeting, cabinetry, certain wiring, parking lot paving, landscaping — many of which the IRS allows to be depreciated over much shorter timeframes. The study is performed by a qualified engineering firm, not estimated; the output is a report that allocates the purchase price across asset classes and supports the accelerated schedule if the IRS ever asks.

2. What Bonus Depreciation Changes

Bonus depreciation lets the entire reclassified short-life portion of the property be deducted in year one, rather than spread across 5 to 15 years. The One Big Beautiful Bill Act restored bonus depreciation to 100%, but the acquisition date matters as much as the placed-in-service date.

For property acquired on or after January 20, 2025 and placed in service in 2026, the rate is 100%.

For property acquired before January 20, 2025, including property under a binding contract signed before that date, the older phase-down schedule still applies. That rate is 20% for 2026.

This distinction catches investors off guard. A property that closed in late 2024 and was placed in service in 2026 does not get 100% bonus depreciation. Confirm the acquisition date before assuming the full deduction is available.

3. Worked Example: A $1.2M Rental Property

Actual results vary by property type, age, and component mix — this is illustrative, not a guarantee, which is why a real engineering study matters.

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4. With vs. Without Cost Segregation

5. Who Should (and Shouldn't) Do a Cost Seg Study

This makes the most sense for owners who either have real estate professional status, qualify under the STR loophole, or have substantial passive income elsewhere to absorb the loss. Without one of those, the accelerated loss may simply be suspended as a passive loss carryforward rather than usable immediately — still valuable, but not the instant cash-flow benefit some expect.

6. State-Specific Considerations

Illinois generally follows federal depreciation rules for individual income tax purposes, so the federal cost segregation benefit largely flows through to the state return as well. Investors with property in multiple states should confirm each state's depreciation conformity, since not all states adopt federal bonus depreciation rules identically.

7. Step-by-Step Process

• Confirm the property is a strong candidate (typically $500K+ purchase price for the study cost to make sense)
• Engage a qualified cost segregation engineering firm
• Provide closing documents, property details, and any renovation records
• Receive the engineering report allocating costs by asset class
• Apply the reclassification and bonus depreciation on the tax return
• Confirm REPS or STR status if the goal is offsetting active income
• Keep the engineering report on file permanently in case of audit

8. Most Common Mistakes

Doing a cost seg without REPS or STR status and expecting an immediate cash benefit. The deduction may be real but suspended as a passive loss until there's passive income to absorb it. Using a DIY or software-only cost segregation study instead of a real engineering study. Forgetting depreciation recapture on sale.

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9. FAQ

How much does a cost segregation study cost? Typically a few thousand dollars depending on property size and complexity — most clients see a return many times that in year-one tax savings.

Can I do this on a property I've owned for years? Yes, through a look-back study.

Does this work on my primary residence? No — cost segregation only applies to income-producing property.