Cost Segregation and Section 199A Deduction: 2026 Guide

A cost segregation study and the Section 199A deduction pull from the same pool of taxable income, so a bigger depreciation write-off this year can mean a smaller 20% deduction on the same rental.

Why this matters

Section 199A gives owners of a qualifying rental trade or business a deduction equal to 20% of qualified business income (QBI), the net income left after expenses and depreciation. Cost segregation increases depreciation in year one, often reclassifying 20% to 45% of a property's depreciable basis into 5-, 7-, and 15-year buckets. That's good news for your bonus depreciation math and bad news for your QBI, because QBI is calculated after depreciation, not before.

Run a study that reclassifies enough basis, and net rental income drops close to zero or slides into a loss. A loss produces no current Section 199A deduction. Instead it becomes a negative QBI carryforward that reduces next year's 199A deduction on other qualifying activities. That's not a reason to skip a study, especially for high-income W-2 earners leaning on accelerated depreciation to offset salary income. It's a reason to run the 199A math alongside the depreciation math before you file in 2026.

Think of it as two dials on the same dashboard. Turn depreciation up, QBI goes down. Understanding which dial matters more to your tax bill this year is the whole point of this guide.

What you'll need

• Last year's Form 8995 or 8995-A showing the QBI reported for the rental
• Current depreciation schedule for the property
• A completed engineering-based cost segregation study (a 100+ page report, delivered in 3-5 business days for a $2,200 flat fee, is standard for a residential rental in 2026)
• Records showing whether the activity meets the Section 199A trade-or-business test
• A CPA willing to model the return both with and without the reclassified depreciation

The steps

1. Confirm your rental clears the 199A trade-or-business bar

Section 199A only applies to activities that rise to the level of a trade or business. IRS Notice 2019-38 offers a safe harbor: 250 hours of rental services per year, separate books and records, and contemporaneous logs. Short of the safe harbor, a facts-and-circumstances test still applies. Claiming real estate professional status unlocks passive losses against W-2 income, but it's a separate test from the 199A trade-or-business standard, and passing one doesn't automatically satisfy the other.

2. Pull your current QBI number before you order anything

Look at your most recent Form 8995 or 8995-A. Note the QBI figure attributed to the rental. This is your baseline. Without it, you can't measure what a cost segregation study will actually do to the 199A deduction.

3. Order the study and read the reclassification percentage

A residential cost segregation study typically moves 20% to 45% of the depreciable basis into short-life property. On a $500,000 short-term rental, a 25% reallocation shifts $125,000 into 5-, 7-, and 15-year buckets eligible for bonus depreciation. That percentage, not a guess, drives every number after this step.

4. Recompute QBI with the new depreciation number

Subtract the accelerated first-year depreciation from net rental income. If the activity showed $60,000 of QBI before the study and the study frees up $125,000 of bonus-eligible depreciation, the rental now reports a loss instead of income. That loss is real and it's not wasted, but it does zero out the current-year 199A deduction on this specific activity.

5. Check the W-2 wage and UBIA limitation

Above the 199A income phase-in range, the deduction gets capped by W-2 wages paid by the business or by 2.5% of the unadjusted basis (UBIA) of qualified property. Rental activities with no employees often lean on the UBIA test. Cost segregation doesn't reduce UBIA, since UBIA uses original unadjusted basis, not the depreciated balance, so this limitation usually isn't the binding constraint for a single STR.

6. Weigh the bonus depreciation savings against the lost 199A deduction

A $125,000 write-off at a 37% bracket saves roughly $46,250 in tax the year it's taken. Losing a 199A deduction on $60,000 of QBI costs $12,000 at the 20% rate. For most owners, the depreciation savings dwarf the lost deduction, and understanding bonus depreciation recapture rules matters more at sale than the 199A trade-off does in year one.

7. File Form 8995 or 8995-A with the updated numbers

Your CPA reports the recalculated QBI, applies any negative QBI carryforward from a prior year, and nets the rental against other 199A-eligible activities if you've made an aggregation election under Reg. 1.199A-4. This is the step where the two numbers finally reconcile on paper.

Troubleshooting

• QBI went negative after the study. The loss carries forward and offsets next year's positive QBI dollar for dollar before any 199A deduction is calculated. It doesn't disappear, it just waits.
• You own more than one rental. An aggregation election can net a loss on one property against income on another, which can preserve some current-year 199A deduction instead of losing it entirely.
• The property has mixed personal and rental use. Only the rental-use share of income, expenses, and depreciation counts toward QBI. Personal-use days need to come out of the calculation before the study's numbers get applied.
• The rental doesn't clear the 250-hour safe harbor. A facts-and-circumstances trade-or-business argument still works, but it needs contemporaneous records, not a reconstruction in April.
• The study lands late in the tax year. Depreciation and the resulting QBI hit still apply based on the placed-in-service date, but a late order leaves less time to model the 199A impact before filing.

Tools and resources

• Form 8995 or 8995-A (whichever applies based on taxable income)
• IRS Notice 2019-38 for the rental safe harbor test
• Reg. 1.199A-4 for aggregating multiple rental activities
• Your current depreciation schedule and a completed engineering-based cost segregation report
• A CPA who will model the return with and without the reclassified depreciation before you file

What to do next

Once the study is in hand, the report itself doesn't change your tax return. Your CPA still has to apply it, and the handoff between a completed report and a filed return is where most of the value either gets captured or lost. Review how a CPA implements a cost segregation report before you send the numbers over, so the 199A recalculation happens in the same pass as the depreciation entries.

FAQ

One last thing

The 199A trade-off is temporary. The depreciation isn't. A cost segregation study that zeroes out this year's 199A deduction still banks the depreciation through bonus depreciation, and the negative QBI carryforward just sits and waits for next year's profit to offset the following year's 199A base. Most owners run this once, see the depreciation savings outweigh the lost deduction by a wide margin, and stop worrying about it.

Related guides

• STR loophole explained for W-2 earners
• How a CPA implements a cost segregation report on a tax return