Section 199A QBI Deduction: Aggregation, SSTB Rules, and Maximizing the 20% Pass-Through Deduction

By Yarik Yarosh, CPA ·September 5, 2026 ·5 min read

Written by Yarik Yarosh, CPA (US & Canada) September 5, 2026 · FL CPA license AC61704 · CPA Ontario

IRC 199A provides a deduction equal to 20% of qualified business income (QBI) from pass-through entities (sole proprietorships, partnerships, S-Corps, and certain trusts/estates). The deduction was enacted under the TCJA and made permanent by the OBBBA. For taxpayers below the income threshold ($191,950 single, $383,900 MFJ for 2025), the deduction is straightforward: 20% of QBI, limited to 20% of taxable income. Above the threshold, the deduction is subject to wage and property limitations, and specified service trades or businesses (SSTBs) lose the deduction entirely once fully phased out. The QBI deduction reduces income tax but NOT self-employment tax.

✓Key takeaway

QBI deduction calculation:

Below the threshold ($191,950 single / $383,900 MFJ, 2025): QBI Deduction = 20% of QBI (no further limitations)

Above the threshold (phase-in range: $50,000 single / $100,000 MFJ above threshold): QBI Deduction = LESSER of:

20% of QBI, OR
The GREATER of:
- 50% of W-2 wages paid by the business, OR
- 25% of W-2 wages + 2.5% of UBIA (unadjusted basis immediately after acquisition) of qualified property

SSTBs above the threshold:

Taxable Income	SSTB QBI Deduction
Below $191,950 (S) / $383,900 (MFJ)	Full 20% deduction
Phase-in range ($50K single / $100K MFJ)	Proportional reduction
Above $241,950 (S) / $483,900 (MFJ)	ZERO (completely lost)

What qualifies as an SSTB (specified service trade or business):

SSTB (no deduction above threshold)	NOT SSTB (deduction available)
Accounting, law, consulting	All trades (HVAC, plumbing, electrical)
Financial services, brokerage	Construction, manufacturing
Health care (doctors, dentists, therapists)	Retail, wholesale
Performing arts (actors, musicians)	Real estate (agents, brokers, property management)
Athletics (professional athletes)	Engineering, architecture
Bookkeeping	Insurance agents
Actuarial science	Farming

OBBBA updates to QBI (Section 199A made permanent):

The deduction is now PERMANENT (was made permanent by the One Big Beautiful Bill Act)
SSTB phase-out thresholds are indexed for inflation: $266,950 single / $533,900 MFJ (2026)
All other mechanics unchanged

Aggregation election (Reg. 1.199A-4): Multiple businesses can be aggregated if they share:

Common ownership (50% or more of each business)
Two of three factors: centralized purchasing, shared facilities/equipment, shared employees

When aggregated, the businesses are treated as a single trade or business for the W-2 wages and UBIA limitations. This can help when one business has high wages but low income and another has high income but low wages.

How does QBI work with multiple activities?

Hypothetical example

Round numbers. A married couple. Filing jointly. Combined taxable income: $420,000 (above the $383,900 MFJ threshold).

Business 1: Plumbing company (S-Corp) QBI: $200,000 W-2 wages paid: $120,000 (owner salary $70,000 + 2 employees $50,000) UBIA of qualified property: $80,000 (trucks, equipment) SSTB? NO

QBI deduction calculation (above threshold):

20% of QBI: $200,000 x 20% = $40,000
50% of W-2 wages: $120,000 x 50% = $60,000
25% of wages + 2.5% of UBIA: ($120,000 x 25%) + ($80,000 x 2.5%) = $30,000 + $2,000 = $32,000
Greater of wage tests: $60,000
Lesser of 20% QBI or wage test: $40,000
QBI deduction: $40,000

The wage test doesn’t limit this business because W-2 wages are high enough.

Business 2: Consulting practice (sole prop) QBI: $100,000 W-2 wages paid: $0 (no employees, sole prop doesn’t pay owner W-2) UBIA: $5,000 (laptop, desk) SSTB? YES (consulting is an SSTB)

Taxable income: $420,000 (above $483,900 fully phased out? No, $420,000 is in the phase-in range: $383,900 to $483,900) Phase-in calculation: ($420,000 - $383,900) / $100,000 = 36.1% phased in Applicable percentage: 1 - 36.1% = 63.9% of income counts

QBI for SSTB calculation: $100,000 x 63.9% = $63,900 W-2 wages for SSTB: $0 x 63.9% = $0 UBIA for SSTB: $5,000 x 63.9% = $3,195

QBI deduction calculation:

20% of adjusted QBI: $63,900 x 20% = $12,780
50% of adjusted wages: $0 x 50% = $0
25% of wages + 2.5% UBIA: $0 + ($3,195 x 2.5%) = $80
Greater of wage tests: $80
Lesser of 20% QBI or wage test: $80
QBI deduction: $80

The consulting practice gets almost NO QBI deduction because (1) it’s an SSTB in the phase-out range and (2) it has no W-2 wages (sole prop).

The fix for Business 2: S-Corp election + W-2 wages If the consulting practice elected S-Corp and paid the owner a $55,000 salary:

W-2 wages: $55,000 Adjusted wages: $55,000 x 63.9% = $35,145 50% of adjusted wages: $17,573 20% of adjusted QBI: $63,900 x 20% = $12,780 Lesser: $12,780

Revised QBI deduction: $12,780 (vs. $80 without the S-Corp election)

The S-Corp election adds $12,700 in QBI deduction, saving $12,700 x 24% = $3,048 in income tax, on top of the FICA savings from the S-Corp itself.

Aggregation strategy: The plumbing and consulting businesses CANNOT be aggregated because an SSTB cannot be aggregated with a non-SSTB.

If the owner had two non-SSTB businesses (e.g., plumbing and landscaping), aggregation would combine their wages and UBIA, potentially increasing the QBI deduction for the lower-wage business.

Combined QBI deduction:

Scenario	Business 1	Business 2	Total QBI Deduction
No S-Corp for consulting	$40,000	$80	$40,080
S-Corp for consulting	$40,000	$12,780	$52,780

Tax savings from optimizing: $52,780 x 24% = $12,667 vs. $40,080 x 24% = $9,619 Additional annual savings: $3,048

Planning considerations:

SSTBs below the threshold get the full 20% deduction regardless of wages or property
Non-SSTBs above the threshold need W-2 wages (hire employees, elect S-Corp, or pay owner W-2) to maximize the deduction
The S-Corp election creates W-2 wages that count toward BOTH the FICA savings and the QBI wage test
The QBI deduction reduces income tax only, not SE tax
Capital gains and interest income are NOT QBI (they don’t qualify for the 20% deduction)

Illustrative numbers only, not a real client and not advice for your facts.

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Cite this page

Yarik Yarosh, CPA. "Section 199A QBI Deduction: Aggregation, SSTB Rules, and Maximizing the 20% Pass-Through Deduction." Blue Cloud CPA, September 5, 2026. https://bluecloudcpa.com/guides/small-business-section-199a-qbi-aggregation-rules

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.