QBI Deduction Deep Dive: Section 199A Calculation, Limits, and SSTB Rules

By Yarik Yarosh, CPA ·September 5, 2026 ·6 min read

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

The Qualified Business Income (QBI) deduction under IRC 199A allows owners of pass-through businesses (sole proprietorships, S-Corps, partnerships, LLCs) to deduct up to 20% of their qualified business income from their taxable income. This deduction was introduced by the Tax Cuts and Jobs Act (2017), was originally made permanent by the One Big Beautiful Bill Act, and was made permanent by the One Big Beautiful Bill Act (OBBBA). The deduction is taken on the individual return (not the business return), doesn’t reduce self-employment tax, and doesn’t reduce AGI. The calculation is straightforward for most small business owners below the income threshold ($191,950-$241,950 single, $383,900-$483,900 MFJ for 2024; updated to $266,950 single / $533,900 MFJ under OBBBA), but becomes more complex above the threshold due to the W-2 wage/property limit and the SSTB phase-out.

✓Key takeaway

QBI deduction basics:

Below the income threshold:

Deduction = 20% of QBI (or 20% of taxable income before QBI deduction, whichever is less)
No W-2 wage limit
No SSTB restriction
No property limit
Nearly every small business owner below the threshold gets the full 20%

Above the income threshold (OBBBA thresholds):

Single: $266,950 (phase-in range $266,950-$316,950)
MFJ: $533,900 (phase-in range $533,900-$633,900)

For SSTBs above the threshold:

The deduction phases out completely within the phase-in range
Above $316,950 (single) / $633,900 (MFJ): QBI deduction = $0

For non-SSTBs above the threshold:

Deduction limited to the GREATER of:
- 50% of W-2 wages paid by the business, OR
- 25% of W-2 wages + 2.5% of the unadjusted basis of qualified property (UBIA)
This is why S-Corps with employees benefit from the W-2 wage component
Sole proprietors with no employees and no property may see a reduced deduction

What’s an SSTB (Specified Service Trade or Business):

Health care (doctors, dentists, nurses, physical therapists)
Law
Accounting (including tax preparation, bookkeeping)
Actuarial science
Performing arts (actors, musicians, but NOT DJs playing recorded music)
Consulting (providing advice, NOT implementation)
Athletics (professional athletes, coaches)
Financial services (wealth management, investment advice)
Brokerage services
Any business where the principal asset is the reputation or skill of employees/owners

What isn’t an SSTB:

All trades (plumbing, electrical, HVAC, roofing, landscaping, etc.)
Construction
Manufacturing
Retail
Real estate (rental, development)
Restaurants and food service
Transportation and delivery
Technology (software development is NOT consulting if it produces a product)
Architecture and engineering
Insurance agency (selling, not advising)
Notarization (ministerial act, not professional service)

How does the QBI deduction calculation work?

Hypothetical example

Round numbers. Three scenarios showing how QBI works at different income levels and business types.

Scenario 1: Plumber, $80,000 net profit, single filer (BELOW threshold)

QBI: $80,000
20% of QBI: $16,000
Taxable income before QBI: $80,000 - $5,652 (half SE) - $15,750 (standard deduction) = $59,348
20% of taxable income: $11,870
QBI deduction = lesser of: (a) 20% of QBI = $80,000 x 20% = $16,000 (b) 20% of (taxable income before QBI, after other deductions, minus net capital gain) = 20% x $59,348 = $11,870
QBI deduction: $11,870 (taxable income limits it)

If the plumber is married filing jointly: Taxable income before QBI: $80,000 - $5,652 - $31,500 = $42,848 20% of taxable income: $8,570 QBI deduction: $8,570 (limited by the lower taxable income from the larger standard deduction)

Key insight: at lower income levels, the standard deduction reduces taxable income enough that it limits the QBI deduction. A married couple needs about $188,000 in QBI before the 20% of QBI calculation ($37,600) falls below 20% of taxable income.

Scenario 2: Consultant (SSTB), $300,000 net profit, single filer (ABOVE threshold) Taxable income: approximately $270,000 (after deductions) This is ABOVE $266,950 (SSTB threshold).

Phase-out calculation: Excess over threshold: $270,000 - $266,950 = $3,050 Phase-out range: $50,000 ($266,950 to $316,950) Phase-out percentage: $3,050 / $50,000 = 6.1% Applicable percentage: 100% - 6.1% = 93.9%

QBI deduction: $300,000 x 20% x 93.9% = $56,340

At $316,950+ taxable income: QBI deduction = $0.

The consultant loses the ENTIRE deduction above $316,950. At $300,000 QBI, this represents a $60,000 deduction loss, which at 32% marginal rate = $19,200 in additional tax. This is why high-income SSTBs sometimes explore strategies to reduce taxable income below the threshold (retirement plan contributions, charitable giving, income timing).

Scenario 3: S-Corp roofing company (non-SSTB), $400,000 net profit, MFJ (ABOVE threshold) W-2 wages paid by the S-Corp: $180,000 (owner + 3 employees) Qualified property (UBIA): $100,000 (trucks, equipment)

Taxable income: approximately $350,000 (after deductions) This is BELOW $533,900 (MFJ threshold for non-SSTB).

Since below the threshold: QBI deduction = 20% x $400,000 = $80,000. No W-2/UBIA limit applies below the threshold.

Now assume the same business at $600,000 taxable income (ABOVE threshold): QBI deduction = lesser of: (a) 20% x QBI = 20% x $600,000 = $120,000 (b) Greater of:

50% x W-2 wages = 50% x $180,000 = $90,000, OR
25% x W-2 wages + 2.5% x UBIA = 25% x $180,000 + 2.5% x $100,000 = $45,000 + $2,500 = $47,500

QBI deduction: $90,000 (limited by the W-2 wage test)

The W-2 wages of $180,000 support a $90,000 QBI deduction. Without employees (no W-2 wages), the deduction above the threshold would be limited to 2.5% of UBIA = $2,500. This is why non-SSTB businesses above the threshold benefit from having employees on payroll (even if the owner is the only employee via S-Corp).

The S-Corp owner’s salary counts as W-2 wages for QBI purposes. An S-Corp owner paying themselves a $60,000 salary (W-2) supports a $30,000 QBI deduction (50% x $60,000) above the threshold.

Multiple businesses: If a taxpayer has two businesses:

Plumbing S-Corp: $200,000 QBI
Consulting sole prop (SSTB): $100,000 QBI

Below the threshold: QBI deduction = 20% x ($200,000 + $100,000) = $60,000

Above the threshold: the SSTB income ($100,000) is phased out, but the non-SSTB income ($200,000) is limited by W-2 wages/UBIA. Each business is calculated separately, then combined.

Common QBI mistakes:

Claiming QBI deduction on the business return (it goes on Form 1040, not Schedule C or 1120S)
Assuming the QBI deduction reduces SE tax (it does not)
Not realizing that capital gains, interest, and dividends are excluded from QBI
Forgetting that Section 179 reduces QBI (the deduction lowers business income, which lowers QBI)
Not tracking W-2 wages for the above-threshold calculation

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

Related guides:

QBI Deduction for Rental Real Estate: The Safe Harbor Under Rev. Proc. 2019-38

How do specified service trades or businesses affect your QBI deduction?

Specified service trades or businesses (SSTBs) including law, medicine, accounting, consulting, financial services, and performing arts face a phase-out of the QBI deduction at higher income levels. For 2025, the QBI deduction phases out for SSTBs between $191,950 and $241,950 for single filers and $383,900 and $483,900 for joint filers, with zero deduction above the upper threshold. Non-SSTB businesses above the income threshold are limited to the greater of 50% of W-2 wages or 25% of W-2 wages plus 2.5% of the unadjusted basis of qualified property, but they never lose the deduction entirely. The SSTB classification looks at the principal asset of the business, so if more than 10% of gross receipts come from specified service activities (5% for businesses with over $25 million in gross receipts), the entire business is treated as an SSTB.

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Cite this page

Yarik Yarosh, CPA. "QBI Deduction Deep Dive: Section 199A Calculation, Limits, and SSTB Rules." Blue Cloud CPA, September 5, 2026. https://bluecloudcpa.com/guides/small-business-qbi-deduction-section-199a-deep-dive

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