Owning multiple businesses can create more than additional accounting.
It can change the Section 199A calculation.
For owners of pass-through businesses, the qualified business income deduction can generally reach 20 percent of qualifying business income. But once multiple businesses are involved, the calculation may depend on where the income, W-2 wages, qualified property, and losses actually sit.
That creates a structural planning question:
Should qualifying businesses be evaluated separately, or can they be aggregated for Section 199A purposes?
For some owners, the difference can be substantial.
The Problem With Looking at Each Business in Isolation
Consider an owner with several businesses.
One generates substantial QBI but has little or no W-2 wages.
Another has significant wages.
A third holds qualified property.
Looking only at the combined economics can obscure an important issue.
For taxpayers subject to the wage and qualified-property limitations, those attributes generally matter at the business level unless a valid aggregation applies.
As a result, a profitable business with little or no supporting wages or qualified property can potentially produce a reduced Section 199A deduction, even when another commonly owned business has substantial wages.
Aggregation Can Change the Calculation
Section 199A regulations permit certain businesses to be aggregated.
When a valid aggregation is made, the combined QBI, W-2 wages, and qualified property of the aggregated businesses are used for the calculation.
That can produce a materially different result.
The source provides a useful example involving three businesses.
Calculated separately, the businesses produce a combined Section 199A deduction of $37,340.
When the same businesses are properly aggregated, the deduction increases to $94,131.
That is a $56,791 difference in the deduction based on the facts in that example.
The businesses did not suddenly become more profitable.
The structure of the calculation changed.
But Aggregation Is Not a Tax Election You Make Just Because the Math Looks Better
This is the critical limitation.
Businesses must qualify before they can be aggregated.
Among the requirements described in the Section 199A regulations and the source article, the businesses must satisfy ownership and taxable-year requirements, cannot include a specified service trade or business that is ineligible for aggregation, and must satisfy at least two of three operational relationship tests.
Those tests examine whether the businesses:
provide the same or customarily related products or services;
share facilities or significant centralized business functions; or
operate in coordination with, or reliance on, one another.
Once businesses are aggregated, consistency also matters. The aggregation generally must continue to be reported in subsequent years while it remains valid, and an annual disclosure statement is required.
In other words:
The deduction should follow a supportable business structure, not a preferred tax result.
Losses Create Another Layer
Multiple businesses can also interact when one of them loses money.
Negative QBI generally does not stay isolated inside the losing business.
The source explains that negative QBI must be allocated proportionately against positive QBI from the owner's other businesses.
If total QBI becomes negative, there is no Section 199A deduction for that year, and the negative QBI carries forward.
Importantly, the wages and qualified property associated with the loss business do not move with that negative QBI to the profitable businesses.
That can make a business loss more consequential than it first appears.
2026 Makes the Review More Important
Section 199A is now permanent under the legislation discussed in the source.
Beginning in 2026, the source also identifies wider phase-in ranges and a new minimum deduction provision for qualifying taxpayers.
Those changes do not eliminate the structural issues created by multiple businesses.
For higher-income owners in particular, the location of QBI, wages, qualified property, and losses can still materially affect the calculation.
The Planning Question Is Bigger Than the Calculation
The mistake is treating Section 199A as something that gets calculated only after the year is over.
For an owner with multiple entities, the better review asks:
Which businesses generate QBI?
Where are the W-2 wages?
Which businesses hold qualified property?
Is one business generating losses?
Do any businesses satisfy the aggregation requirements?
Is the current reporting position consistent with prior years?
Those are structural questions.
And structural questions are usually more useful before the tax return is being finalized.
Bottom Line
Owning several businesses does not mean their Section 199A attributes automatically work together.
In some cases, each business must stand on its own.
In others, a properly supported aggregation can materially improve the calculation.
The difference can be significant enough that owners with multiple pass-through businesses should review the structure, not simply accept the number produced at filing time.
Own More Than One Business?
If your QBI, payroll, property, and business income are spread across multiple entities, it may be worth reviewing how those businesses interact before the Section 199A deduction is finalized.
Educational only; not tax or legal advice. Section 199A calculations and aggregation eligibility depend on the taxpayer's specific facts and circumstances.