How Cost Segregation Changes the QBI Deduction

By AE Tax Advisors Team · Updated November 6, 2026

Why a gross depreciation number is not the final tax result

A high-income owner with an operating business and real estate may have two deductions interacting on the same return: depreciation and the Section 199A qualified business income deduction. When depreciation is attributable to a qualifying trade or business, it generally reduces that activity's QBI. A projection that counts the depreciation benefit but leaves QBI unchanged can overstate the combined result.

First establish whether the rental qualifies for Section 199A using the rental QBI eligibility guide. This page addresses the next decision: how a cost-seg change affects the calculation after classification and loss usability have been reviewed.

A simplified positive-QBI example

Assume a qualifying activity has $200,000 of QBI before an additional $50,000 of deductible depreciation. Ignore wage/property limits, taxable-income limits, other deductions, state tax and any other activity. At a full 20% QBI calculation, the component would fall from $40,000 to $30,000. The $50,000 depreciation deduction is partly offset by a $10,000 smaller QBI deduction, producing a simplified $40,000 reduction in income after those two deductions rather than $50,000.

This is an illustration of the interaction, not a tax quote. At high income, wage and property limits or SSTB restrictions can change the result. Other deductions, gains and losses can also change the household calculation. Run the complete return comparison rather than applying this illustration as a universal 80% rule.

What if cost segregation creates negative QBI?

Losses from a qualified business can offset positive QBI from other qualified businesses under the applicable netting rules. If total QBI is negative, a carryforward can reduce QBI in a later year. A separate LLC does not necessarily keep that loss out of the owner's combined Section 199A calculation. Keep QBI loss records distinct from passive-loss and net-operating-loss records.

Also distinguish a loss currently allowed on the return from one suspended under another limitation. The Section 199A treatment of a previously suspended loss depends on the applicable rules and when it becomes deductible. Ask the preparer to identify the relevant year and category rather than inserting the engineering study's total directly into a QBI worksheet.

UBIA is not simply the depreciated book balance

For owners subject to wage/property limits, unadjusted basis immediately after acquisition of qualified property is a separate concept from adjusted tax basis. A depreciation deduction does not automatically reduce UBIA by the same amount. Whether an asset remains qualified property depends on the applicable holding, use and depreciable-period rules. Maintain an asset-level UBIA schedule instead of copying net book value.

A cost-seg study changes asset classifications and schedules. Reconcile the revised fixed-asset ledger, recovery periods, service dates and Section 199A information. Do not assume either that all UBIA disappears after bonus depreciation or that every asset remains eligible indefinitely.

Compare the same owner facts with and without the study

Confirm rental business status and any applicable SSTB treatment.
Determine incremental depreciation and whether the owner can deduct it currently.
Recompute each activity's QBI, netting and carryforwards.
Recompute wage/property and household taxable-income limits.
Compare total federal tax, state adjustments, fees and future deductions.
Include the planned holding period and later sale consequences.

For a building leased to your own company, self-rental and grouping questions belong before the calculation. For a conventional rental, loss usability may be the first constraint.

What to ask for in the projection

Request two complete scenarios on identical income and ownership assumptions. Each should show depreciation, currently allowed losses, QBI deductions, QBI-loss carryforwards, state differences and the cash needed for implementation. The adviser should explain why the net tax change differs from the headline depreciation deduction. A smaller QBI deduction does not mean cost segregation is always wrong; it means the decision must use the combined result.

Questions business owners ask

Does cost segregation reduce my QBI deduction?

It can. Depreciation attributable to a qualified business generally reduces QBI, but the actual deduction also depends on netting, income, wage/property and other limits.

Does bonus depreciation erase the property basis used for QBI limits?

Not automatically. UBIA is different from adjusted tax basis. Check whether each asset is qualified property and remains within the relevant depreciable period.

Should I avoid cost segregation if it reduces QBI?

Not necessarily. Compare the combined tax result, current loss usability, state effects, fees and future consequences rather than evaluating either deduction alone.

Coordinate the business, property and household return

Bring the ownership chart, relevant returns, property depreciation schedules and the decision deadline to a discovery call. Ask for a written scope identifying planning, implementation, return preparation and study responsibilities. These services are separately scoped; a public article is not a completed plan for your facts.

Fees and engagement scope · Book a Cost Seg Discovery Call

Sources and review context

General educational information prepared with AI assistance, not an individual tax opinion or a representation of professional signoff. Examples are hypothetical and do not represent client results. Verify the rules for the applicable year and state with your tax advisor before acting. Editorial policy · AI disclosure