Brother-Sister Relationships: Understanding the Tax Code
Understanding Brother-Sister Relationships in the Tax Code
Owning several businesses does not always mean the tax code treats each company as completely unrelated. Controlled-group rules can connect businesses through common ownership and affect retirement plans, employee benefits, deductions, tax thresholds, and other calculations. Here is how the brother-sister controlled group concept works and why business owners should pay attention to it.
A business owner may form several separate corporations or other entities for perfectly valid legal, operational, or financial reasons. One company might hold real estate, another might operate the primary business, and a third could provide a different service altogether.
Legally, those businesses may remain separate. For certain federal tax and employee-benefit provisions, however, common ownership can cause multiple businesses to be treated together under controlled-group or common-control rules.
One of the most important structures to understand is the brother-sister controlled group. Despite the name, it does not mean two companies literally have to be owned by biological brothers or sisters.
What Is a Brother-Sister Controlled Group?
Think Common Ownership — Not Family Nicknames.
A brother-sister relationship generally describes two or more businesses whose ownership is sufficiently concentrated among the same small group of owners to satisfy the controlled-group rules applicable to the tax provision being analyzed.
The term can be confusing because it sounds like a family relationship. It is really an ownership relationship between businesses.
The same individual can own two companies and create a brother-sister structure. Several unrelated individuals can also collectively own multiple companies in percentages that satisfy the applicable ownership tests.
The Three Main Controlled-Group Structures
Controlled groups are generally discussed in three broad structures.
Parent-Subsidiary
One corporation owns a sufficiently large interest in another corporation, creating a chain of ownership under the controlled group rules.
Brother-Sister
The same limited group of owners holds sufficient ownership interests across two or more businesses.
Combined Group
A larger structure exists in which corporations are connected through a combination of parent-subsidiary and brother-sister relationships.
Understanding the Ownership Tests
This is where brother-sister controlled-group analysis becomes technical. The applicable test depends in part on which Internal Revenue Code provision is using the controlled-group definition.
Common Ownership Test
For many provisions incorporating the brother-sister controlled-group rules, the same five or fewer individuals, estates, or trusts must collectively own at least 80% of each business being tested.
Identical Ownership Test
Those same owners must possess more than 50% of each business when ownership is counted only to the extent that each person's ownership is identical across the businesses.
Why You Will Sometimes See Different Explanations of the 80% Test
Section 1563 contains different applications of the brother-sister definition depending on the Code provision involved. That is why a controlled-group analysis should start with the specific tax or benefit rule being applied rather than assuming that one simplified ownership formula answers every controlled-group question.
The underlying principle remains the same: the IRS is looking for substantial common control across the businesses.
A Simple Brother-Sister Ownership Example
Assume two owners hold interests in two separate corporations.
| Owner | Company A | Company B | Identical Ownership |
|---|---|---|---|
| Owner 1 | 70% | 60% | 60% |
| Owner 2 | 30% | 40% | 30% |
| Combined | 100% | 100% | 90% |
Count Only the Percentage Each Owner Holds in Both Companies.
Owner 1 owns 70% of Company A but only 60% of Company B. Only 60% is identical between the two businesses.
Owner 2 owns 30% of Company A and 40% of Company B. Only 30% is identical.
The identical ownership total is therefore 60% + 30% = 90%.
This example easily exceeds a more-than-50% identical ownership threshold and also reflects substantial common ownership of both corporations.
Direct Ownership Is Not Always the Entire Story
Controlled-group analysis becomes more complicated because federal tax law contains attribution rules.
Attribution can cause a person to be treated as owning interests that are technically held by another person or entity.
Family Attribution
Certain ownership held by spouses, children, parents, grandchildren, and other family relationships may be attributed under applicable rules.
Entity-to-Owner Attribution
Interests owned through partnerships, estates, trusts, or corporations may need to be traced through to their underlying owners.
Owner-to-Entity Attribution
In certain circumstances, ownership held by an owner may also be attributed to an entity.
Options and Constructive Ownership
Certain rights to acquire stock and other constructive-ownership rules can affect the ownership calculation even before actual ownership changes hands.
This Is Why a Cap Table Alone May Not Be Enough
A controlled-group analysis sometimes requires more than simply looking at the names listed on corporate stock records. Family relationships, trusts, partnerships, corporate ownership, options, and other constructive ownership rules may change the tax result.
Why Brother-Sister Controlled Group Status Matters
Controlled-group rules exist in part to prevent taxpayers from dividing one economic enterprise among several entities simply to obtain multiple tax limits or employee-benefit advantages that would not be available to a single business.
Retirement Plans
Related employers may need to be treated as a single employer when applying certain retirement-plan eligibility, coverage, nondiscrimination, and other qualification rules.
Employee Benefits
Common ownership can affect whether employees of several businesses must be considered together when applying benefit rules.
Section 179
Controlled-group rules can require component members to share a single Section 179 limitation instead of allowing each member an independent limitation.
Gross-Receipts Tests
Certain tax provisions require businesses under common control to aggregate gross receipts when determining whether a taxpayer meets a small-business threshold.
Employer Size Tests
Related employers may be aggregated when determining whether an employer satisfies certain employee-count thresholds.
Corporate Tax-Benefit Items
Certain corporate tax-benefit items and limitations can be allocated or applied across members of a controlled group rather than independently to each corporation.
Multiple Corporations Do Not Necessarily Mean Multiple Full Deduction Limits.
For Section 179 purposes, the tax code contains specific controlled-group rules that can treat component members as one taxpayer when applying the applicable dollar limitations.
The IRS's 2025 Form 4562 instructions specifically state that for a controlled group, all component members are treated as one taxpayer for the Section 179 limitation.
Controlled Groups Can Be Especially Important for Retirement Plans
Retirement-plan compliance is one of the areas where business owners most commonly encounter controlled-group rules unexpectedly.
Imagine an owner has one business with several employees and another business with only the owner or highly compensated employees.
It may be tempting to establish a generous retirement plan for one company while simply ignoring employees of the other company. Controlled-group rules can prevent that structure from being analyzed as though the employers were completely unrelated.
Separate EINs Do Not Necessarily Mean Separate Employers for Benefit Testing.
Under applicable retirement-plan controlled group rules, related employers may be treated as a single employer for qualification and testing purposes. That can affect which employees must be considered when evaluating the plan.
The IRS describes employers related under controlled-group rules as being treated together for various retirement-plan purposes. :contentReference[oaicite:2]{index=2}
Employee Counts May Need to Be Combined
Common ownership can also matter when a federal tax provision asks how large an employer is.
For example, under the Affordable Care Act, companies with a common owner or otherwise related under certain Section 414 rules are generally combined when determining applicable large employer status. :contentReference[oaicite:3]{index=3}
Two “Small” Companies Can Sometimes Become One Larger Employer for a Tax Test.
If related businesses are required to aggregate employees, looking at each company's headcount separately can produce the wrong conclusion.
This is one reason ownership analysis should occur before assuming that an employee-count threshold does or does not apply.
Gross Receipts May Also Need to Be Aggregated
Several tax provisions provide special treatment to taxpayers that remain under a specified gross-receipts threshold.
The catch is that businesses under common control sometimes cannot simply test each entity's revenue separately.
Aggregation rules can require the gross receipts of related businesses to be combined when determining whether a taxpayer qualifies for a small-business exception. :contentReference[oaicite:4]{index=4}
Splitting Revenue Among Several Entities Does Not Automatically Create Several Small Businesses for Every Tax Rule
When the tax code includes an aggregation requirement, related entities may need to combine their receipts before applying the applicable threshold.
Do Brother-Sister Corporations File One Consolidated Tax Return?
Controlled Group Status Does Not Automatically Create a Consolidated Return.
Brother-sister controlled-group rules and consolidated corporate return rules are related areas of tax law, but they are not the same thing.
A consolidated federal corporate return generally requires an affiliated group meeting the ownership requirements of Section 1504, including a qualifying common parent.
Two corporations owned directly by the same individual do not automatically satisfy that parent-subsidiary structure merely because they are a brother-sister controlled group.
In many common brother-sister structures, each corporation continues filing its own federal income tax return while controlled-group rules are applied to particular tax calculations.
Common Brother-Sister Controlled Group Misconceptions
“The Owners Have to Be Brothers or Sisters.”
No. The phrase describes common ownership of businesses. The owners do not need to be siblings or even related to each other.
“Different EINs Mean the Companies Are Unrelated.”
No. Separate legal entities and EINs can still be aggregated under controlled-group or common-control rules for particular tax provisions.
“Every Controlled Group Has to File One Tax Return.”
No. Controlled-group status does not itself require brother-sister corporations to file a consolidated federal return.
“I Can Give Each Company Its Own Full Tax Limit.”
Not always. Some Code provisions aggregate controlled-group members and require them to share or jointly apply a particular limitation.
“Only Direct Ownership Counts.”
Constructive and attributed ownership can alter the analysis depending on the applicable rules.
“Once We Analyze It, We Never Have to Look Again.”
Ownership changes, new entities, acquisitions, transfers, trusts, options, and changes in family ownership can all change the result.
How to Review a Multi-Entity Business Structure
Controlled-group analysis should be part of the annual review for owners who hold interests in multiple businesses.
List Every Related Business
Include corporations, partnerships, LLCs, trusts, holding companies, and other businesses in which the relevant owners hold interests.
Map Direct Ownership
Document the ownership percentage, voting rights, and value interests held by every relevant owner in each entity.
Review Attribution Rules
Determine whether family, entity, trust, partnership, option, or other constructive ownership changes the direct ownership picture.
Identify the Specific Tax Rule
Do not analyze “controlled group” status in the abstract. Determine which Code provision is being applied because the precise ownership test and consequences can vary.
Review Employee Benefits
Evaluate retirement-plan eligibility, coverage, nondiscrimination, employee counts, and other benefit issues across the related businesses.
Review Tax Limits and Thresholds
Identify tax provisions that aggregate gross receipts, deductions, credits, employee counts, or other limits among related entities.
Repeat the Review After Ownership Changes
A stock transfer, new partner, estate plan, trust transfer, sale, option, or formation of another company can alter controlled-group status.
When Professional Controlled-Group Review Makes Sense
Owners with a single straightforward business may never encounter these rules. Owners of multiple companies should be much more cautious.
A formal review becomes especially valuable when:
- One person or family owns several operating companies.
- The same partners own multiple entities in different percentages.
- One company has employees while another primarily benefits owners.
- Several companies maintain separate retirement plans.
- A new entity is being formed or acquired.
- Ownership interests are being transferred among family members.
- Trusts or estate-planning entities hold business interests.
- A tax strategy depends on a gross-receipts or employer-size threshold.
- Several related companies are purchasing substantial Section 179 property.
Several Companies Can Create One Much Bigger Tax Picture.
At Azalea City Tax & Accounting, we work with business owners to review entity structures, ownership relationships, tax planning, retirement-plan considerations, compensation, related-party transactions, and other issues that arise when several businesses are under common ownership.
Explore Business Tax PlanningFrequently Asked Questions About Brother-Sister Controlled Groups
Do the owners actually have to be brothers and sisters?
No. “Brother-sister” describes the relationship between commonly owned businesses. The owners can be one individual, several unrelated individuals, family members, estates, trusts, or another ownership structure that satisfies the applicable rules.
What is the 50% identical ownership test?
Identical ownership generally counts each relevant owner's ownership only to the lowest percentage that person owns across the businesses being compared. Those identical percentages are then combined to determine whether the applicable more-than-50% threshold is satisfied.
Is there always an 80% ownership test?
Not in exactly the same manner for every provision of the Internal Revenue Code. Section 1563 contains different applications of the brother-sister definition depending on the provision incorporating the controlled-group rules. That is why the specific tax or benefit rule must be identified before applying the ownership test.
Do brother-sister corporations file one consolidated federal tax return?
Not automatically. Consolidated federal corporate returns generally require an affiliated group satisfying separate common-parent ownership requirements. Brother-sister corporations commonly continue filing separate returns while controlled-group rules are applied to specific tax calculations.
Can controlled-group rules affect my 401(k)?
Yes. Related employers may need to be treated as one employer when applying various retirement-plan eligibility, coverage, nondiscrimination, and other qualification rules.
Can each company take its own full Section 179 deduction?
Not necessarily. Section 179 contains specific controlled-group provisions under which component members can be treated as one taxpayer for purposes of the applicable dollar limitation.
Do family ownership rules matter?
They can. Constructive ownership and family attribution rules may cause ownership to be treated differently from the percentages shown directly on corporate or entity records.
Can creating another LLC avoid controlled-group rules?
Simply forming another legal entity does not necessarily avoid aggregation. Controlled-group and common-control rules examine ownership and the particular tax provision involved, rather than relying only on whether the businesses have separate names, EINs, bank accounts, or legal entities.
Should controlled-group status be reviewed every year?
For owners of multiple entities, periodic review is wise, particularly after ownership transfers, formation of new entities, acquisitions, family transfers, trust changes, or other restructuring.
Own More Than One Business? Make Sure the Tax Code Isn't Treating Them Differently Than You Are.
Separate companies can still become connected for retirement-plan rules, employee counts, deduction limits, gross-receipts tests, and other federal tax provisions. If you own interests in several businesses, we can review the ownership structure and help identify where controlled-group or common-control rules may affect your tax planning.