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A cost segregation study does not cancel your Section 199A qualified business income (QBI) deduction, and it does not make the deduction worth less than the tax savings it creates. It moves deductions into the first year, which lowers the net rental income the 20 percent QBI deduction is calculated on. When you have other qualifying business income to absorb the loss, that costs you about 20 percent of the incremental benefit, and the accelerated deduction still saves far more tax than the QBI deduction you give up. Knowing exactly how the two interact lets you plan the year instead of being surprised at filing time.
Hank and Carol live in Shreveport, Louisiana, and file jointly. Hank runs a landscaping company that throws off about $250,000 of qualified business income a year. Carol manages their rental portfolio full time and qualifies as a real estate professional. In late October they sit down with their CPA, who is looking at a rough projection of their 2026 return.
The CPA says something that sounds like bad news. "If we do a cost segregation study on the apartment building you closed on this year, your rental income turns into a large paper loss. That is good for your ordinary income. It also shrinks your QBI deduction, because the deduction is calculated on net business income, and a rental loss reduces it."
Hank frowns. "So the study costs us the 20 percent deduction?"
It is the right question. Hank and Carol give up part of the QBI deduction and come out well ahead anyway, and the arithmetic below shows exactly how far ahead.
Section 199A lets owners of pass-through businesses deduct up to 20 percent of their qualified business income. Pass-throughs include sole proprietorships, partnerships, S corporations and rental real estate that flows to an individual return on Schedule E or a K-1. The deduction is taken below the line, reducing taxable income but not adjusted gross income, on Form 8995 or 8995-A.
The deduction was scheduled to expire after 2025. The One Big Beautiful Bill Act made it permanent at 20 percent and widened the income phase-in range for the wage and property limitations to $75,000 for single filers and $150,000 for joint filers for tax years beginning after December 31, 2025, which matters for owners near the thresholds.
For 2026, the threshold amounts under Revenue Procedure 2025-32 are $201,750 for single filers and $403,500 for joint filers. Below the threshold, the deduction is the lesser of 20 percent of QBI or 20 percent of taxable income less net capital gain, and the wage and property limits do not apply. Above it, those limits phase in over the range, which ends at $276,750 single and $553,500 joint, and then apply in full. That is where unadjusted basis of qualified property, UBIA, enters the picture for real estate owners.
The deduction applies only to income from a trade or business under Section 162, and rental real estate is sometimes a trade or business and sometimes an investment, depending on the facts. Revenue Procedure 2019-38 gives a safe harbor: separate books for each rental enterprise; at least 250 hours of rental services a year by you or your agents (advertising, leasing, screening, collecting rent, operations, maintenance and supervising the people who do that work, but never financial management, capital improvements or travel); contemporaneous records; and a statement attached to the return each year. Triple net leased property and residences you use are excluded. Failing the safe harbor means you rely on the facts-and-circumstances test instead; it does not mean the rental fails.
Rental to a business under common control is treated as a trade or business, which is why QBI comes up so often with owners who lease a building to their own operating company. That structure has its own pitfalls for cost segregation, covered in why a cost segregation loss gets stuck in a self-rental. Short-term rental owners should also note that the seven-day average stay rule that keeps many short-term rentals out of the passive category is a separate test from the trade-or-business question; ask your CPA the QBI question on its own.
A study does not change what you paid or the total depreciation you will ever claim. It changes timing. An engineer separates the building into components, identifying what the engineering supports as 5-year, 7-year and 15-year property instead of 27.5-year or 39-year real property, and property acquired and placed in service after January 19, 2025 generally qualifies for 100 percent bonus depreciation, so the reclassified components are deducted in the first year. See our guide to 100 percent bonus depreciation after OBBBA.
Depreciation is an expense that reduces rental income, and QBI is net income after expenses. So when a study pulls a large amount of depreciation into year one, it reduces that rental's QBI in year one, and the 20 percent deduction falls with it. Three rules govern what happens next.
The loss has to be usable before it reduces QBI. Losses disallowed under Sections 461(l), 465, 469, 704(d) and 1366(d) enter QBI in the year they are allowed, oldest first. A passive investor with a suspended cost segregation loss has no QBI effect in the study year; it arrives when the loss is finally used. Our article on suspended passive losses explains when.
Losses are netted against your other QBI. If Hank has $250,000 of QBI from landscaping and the rental produces a $140,000 loss, net QBI is $110,000. The loss shrinks the pool the 20 percent applies to.
If the net is negative, it carries forward. No QBI deduction is allowed that year, and the net loss is treated as a loss from a qualified business next year, reducing next year's QBI. The deduction you give up is deferred rather than erased.
These are illustrative round figures on the 2026 joint-filer brackets. Before any QBI deduction and before any study, Hank and Carol's 2026 taxable income is $380,000, below the $403,500 threshold, so the wage and property limits do not apply. Their QBI is $250,000 from landscaping and $60,000 of net income from Carol's rentals, $310,000 in all.
Without a study. The QBI deduction is the lesser of 20 percent of $310,000, which is $62,000, or 20 percent of $380,000, which is $76,000. So it is $62,000. Taxable income after the deduction is $318,000, and the federal income tax on that is about $61,516.
With a study. The apartment building closed in March 2026 and was ready for tenants in April 2026, with $780,000 of depreciable basis after land. The study reclassifies about $205,000 of that basis, 26 percent, into 5-, 7- and 15-year property, all deducted under 100 percent bonus with no proration. The $575,000 that stays on 27.5 years takes $14,812 in year one at the April mid-month table rate of 2.576 percent, against $20,093 the whole $780,000 would have taken. The net increase in first-year depreciation is $199,719, rounded to $200,000 for the rest of the example. Carol is a real estate professional who materially participates, so the loss is nonpassive, and at $140,000 it sits well under the Section 461(l) cap for 2026 of $512,000 joint ($256,000 single), adjusted annually. Here is what changes:
Federal income tax falls from about $61,516 to about $24,184, a saving of roughly $37,332.
Had the QBI deduction stayed at $62,000, taxable income would have been $118,000 and the tax about $15,384, a saving of about $46,132. The QBI interaction therefore cost Hank and Carol about $8,800. The $200,000 deduction reduced their QBI deduction by 20 percent of $200,000, or $40,000, and that $40,000 of lost deduction is worth about $8,800 at their marginal rates.
That is the whole story. A $37,332 tax reduction in year one, in exchange for about $8,800 of QBI deduction they would otherwise have kept. They keep roughly 81 cents of every dollar the study would have delivered with no QBI interaction, and they get it now.
When your other QBI is positive and large enough to absorb the rental loss, and the wage and property limits are not binding, each dollar of accelerated depreciation reduces taxable income by one dollar and the QBI deduction by 20 cents. The net reduction is 80 cents, so the net tax saving is your marginal rate times 0.80.
| Marginal federal rate | Savings per $1 of deduction (no QBI interaction) | Net savings per $1 after QBI interaction |
|---|---|---|
| 24% | 24.0 cents | 19.2 cents |
| 32% | 32.0 cents | 25.6 cents |
| 35% | 35.0 cents | 28.0 cents |
| 37% | 37.0 cents | 29.6 cents |
For an owner at 37 percent, a $500,000 first-year deduction saves roughly $148,000 after the QBI interaction instead of $185,000. That reduction is real, and it does not change the decision. The rule of thumb breaks down when the taxable income limit binds, when the wage and property limits apply, when the loss is suspended, or when total QBI is negative.
The QBI deduction is capped at 20 percent of taxable income less net capital gain. In the example above, 20 percent of taxable income was $36,000 and 20 percent of QBI was $22,000, so QBI governed; a bigger study or smaller other income could flip that. This matters most for owners with modest income who buy a large property. If the deduction pushes taxable income near zero, the overall benefit is set by how much income there is to offset, and unused losses carry forward; we explain how in our guide to the 2026 excess business loss limit and cost segregation.
Above the threshold, the QBI deduction on each business is capped at the greater of 50 percent of the W-2 wages paid by the business, or 25 percent of W-2 wages plus 2.5 percent of the unadjusted basis immediately after acquisition of qualified property. That second number is UBIA. Most rental owners pay no W-2 wages, so for them the 2.5 percent of UBIA alternative is the only route to a full deduction above the phase-in range.
Three UBIA rules matter. Bonus depreciation does not reduce UBIA, which is original cost basis at placed-in-service. Land is excluded, which is why the allocation matters; see our post on land value allocation. And each component stays in UBIA for the longer of 10 years or its recovery period, so a reclassified 5-year or 7-year component drops out after 10 years and a 15-year land improvement after about 15, while the building stays for 27.5 or 39.
Here is how much room most owners have. Joanne, a single filer in Monroe, Louisiana, with taxable income well above the phase-in range, owns a $2,000,000 apartment building with $300,000 on land, so $1,700,000 of UBIA and no W-2 wages. Her QBI deduction limit for the property is 2.5 percent of $1,700,000, or $42,500. That limit bites only when 20 percent of the property's QBI exceeds it, which means QBI above 12.5 percent of UBIA, here $212,500 a year. A typical mortgaged rental's net income sits well below that, so the UBIA limit is rarely binding; it matters for a property with little debt and strong cash flow.
Owners who worry that "bonus depreciation uses up the basis that supports the QBI deduction" are mixing up tax basis, which bonus reduces, with UBIA, which it does not.
The interaction runs both ways. Capital gain, including Section 1231 gain treated as long-term capital gain and unrecaptured Section 1250 gain taxed at up to 25 percent, is excluded from QBI. Ordinary income from Section 1245 recapture on the 5-, 7- and 15-year components is included in QBI, so that recapture may carry a 20 percent QBI deduction when you sell. The deduction on the way in costs a slice of QBI deduction now; the recapture on the way out may earn some of it back. For the full picture, read what happens to depreciation recapture when you sell. A 1031 exchange can defer the Section 1245 recapture, subject to the replacement property holding enough Section 1245 property to absorb it.
The real estate professional with other business income. This is Hank and Carol. The loss is usable, the other QBI absorbs it, and the interaction costs about 20 percent of the incremental benefit. Our guide to real estate professional status and cost segregation covers qualification.
The investor with only rental income. A large first-year deduction can push net QBI negative. If the loss is usable, you reduce ordinary income at your full marginal rate, the QBI deduction for the year is zero, and the negative QBI carries forward. The time value of money still favors taking the deduction now.
The passive investor with a suspended loss. Nothing changes in the study year. The deduction creates a suspended loss, and the QBI effect arrives when the loss is allowed. Structure and the grouping election matter here; have your CPA look at both before you decide.
A look-back study on a property placed in service in a prior year takes the missed depreciation through Form 3115 as a catch-up in the current year, and it affects QBI that year the same way. Model it before year-end, and if you hold several properties you can sequence studies across years, as we cover in which building to study in which year.
Ignoring QBI in the projection. A CPA projects the benefit at the marginal rate on the full deduction and the client is surprised the savings are smaller. Model the interaction up front, with the numbers from the proposal.
Not tracking suspended losses for QBI. Losses suspended under Sections 465, 469 or 704(d) enter QBI in the year they are allowed, oldest first. If nobody tracks them, the deduction is wrong in the year they release.
Dropping the Rev. Proc. 2019-38 statement. Owners who rely on the safe harbor must attach the statement each year. Missing it turns a safe harbor into an argument about the facts.
Missing K-1 reporting. For partnerships, QBI, W-2 wages and UBIA are reported in Box 20, Code Z, with a Section 199A statement. If the partnership does not report UBIA, the owner is treated as having none from it.
Treating the choice as all or nothing. Both are available in the same year. The question is the net result after modeling both.
Every figure in the QBI model starts with the depreciation number, so that number has to hold. The IRS Cost Segregation Audit Techniques Guide describes six common approaches, and a fully engineered and accounted study works under the first two: detailed engineering from actual cost records, or engineering with documented estimates reconciled to actual cost. Each component is identified, costed and assigned to a recovery period with the authority behind it, and the result is a component schedule your CPA imports and an examiner can trace line by line, signed by credentialed professionals and defended for as long as you own the building. The same schedule gives your CPA the UBIA of each component and the year it drops out, which the estimated study, a percentage on a page, cannot. We walk through what the guide expects in our summary of the 13 elements of a quality study.
Skip the study if the building has under $180,000 of depreciable basis after land; the fee eats the benefit. Skip it if you plan to sell within a couple of years with no exchange planned, because Section 1245 recapture at ordinary rates can outweigh the time value of the deduction. Think hard if the loss will sit suspended for years with no passive income to absorb it and no path to nonpassive treatment; the QBI question is moot until the loss releases, and the cash benefit arrives late. And if your income is modest and the study would push taxable income near zero, the deduction is worth far less than 37 cents on the dollar in the year it lands, so talk to your CPA about timing first.
It can. Accelerated depreciation reduces the net rental income that counts as QBI, so the 20 percent deduction is calculated on a smaller number that year. The reduction is about 20 percent of the incremental depreciation, and the tax saved by the depreciation itself is usually much larger.
Under Revenue Procedure 2025-32, $201,750 for single filers and $403,500 for joint filers. The phase-in range ends at $276,750 single and $553,500 joint, and above that the wage and property limits apply in full.
No. UBIA is the original basis of qualified property when placed in service, before bonus, Section 179 or regular depreciation. Land is excluded.
It depends on the facts. The Rev. Proc. 2019-38 safe harbor requires separate books, 250 or more hours of rental services a year, contemporaneous records and a statement on the return. Triple net leased property and residences are excluded. Outside the safe harbor, the general trade-or-business standard applies, and that is a question for your CPA.
No QBI deduction that year, and the negative amount carries forward as a loss from a qualified business next year. You still get the ordinary-income benefit of the depreciation if the loss is usable under the passive activity and excess business loss rules.
Ordinary income from Section 1245 recapture generally does. Capital gain and Section 1231 gain treated as capital gain, including unrecaptured Section 1250 gain, do not.
In nearly every case we see, no. The tax saved by the accelerated depreciation is typically many times larger than the QBI deduction given up. Model both together and compare the total tax with and without the study.
Hank and Carol asked their CPA to run the numbers both ways, saw a first-year federal tax reduction of more than $37,000 with the QBI interaction already priced in, and went ahead. You can do the same. Send Jim Dougherty and his team at Cost Seg America your closing statement and a few photos, and you will have a free proposal within 24 hours. Hand the estimate to your CPA and let the math make the call. Call 1-888-365-5023 or email info@costsegamerica.com.
This article is for general educational purposes and does not constitute tax, legal, or accounting advice; tax outcomes depend on your individual facts, so consult your CPA before acting.
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