IRC Section 52: Controlled Groups, Attribution, and Schedule O

The controlled group rules under IRC Section 52 require every employee of commonly owned businesses to be counted as if they all worked for one employer when figuring the Work Opportunity Tax Credit and several related credits. Section 52(a) does this for corporations by pointing to the ownership tests in Section 1563(a); Section 52(b) extends the same treatment to partnerships, sole proprietorships, and LLCs under common control.¹ Splitting a workforce across a family of entities does not multiply credits and does not slip any single entity below a headcount threshold.

The reach goes well past the WOTC. The same ownership definitions power Section 414(b) and (c) for retirement plans,² so a group formed for credit purposes is almost always a group for plan testing too. Everything below turns on whether your entities meet one of the three group definitions and, if so, what changes.

The Three Kinds of Controlled Groups

Parent-Subsidiary

A parent-subsidiary group exists when one corporation owns, directly or indirectly, at least 80% of another corporation’s voting power or stock value.³ Meeting either measure is enough. If Corporation A holds 85% of the value of B’s stock but only 75% of the voting power, the group exists because value passes. Control travels down chains: if A owns 80% of B and B owns 90% of C, all three are in one group with A at the top.

Brother-Sister

Brother-sister groups share owners rather than a vertical chain. A group exists when the same five or fewer individuals, estates, or trusts own more than 50% of each corporation’s voting power or stock value, counting only each owner’s identical stake across the entities.³ Identical ownership uses each person’s smallest percentage across the entities in the test.

Say Owner X owns 60% of Corporation 1 and 40% of Corporation 2. Only 40% counts. Owner Y owns 20% of Corporation 1 and 30% of Corporation 2, so 20% counts. Together, 40% plus 20% is 60%, which clears the 50% threshold and creates the group.

For retirement plan aggregation under Section 414(c), regulations add a second requirement on top of the identical ownership test: the same five or fewer persons must also collectively own at least 80% of each entity.⁴

Combined

A combined group forms when three or more entities are linked by both patterns at once. A parent sits atop a subsidiary and is itself part of a brother-sister pair with a separately owned company; all three become one group.⁵

Attribution: Stock You Are Treated as Owning

Whether direct holdings actually cross the 80% or 50% line usually depends on the constructive ownership rules in Section 1563(e). Attribution is mandatory, not optional, and it regularly pushes ownership over the threshold when no single person’s direct stake would do it alone.

Options and Convertibles

If you hold an option to buy stock, you are treated as owning that stock now.⁶ It does not matter whether the option is currently exercisable or whether you could afford to exercise it. Warrants and convertible debt get the same treatment.

Partnerships, Estates, and Trusts

Stock owned by a partnership is attributed to any partner with at least a 5% interest in capital or profits, based on the larger of the two.⁶ Stock owned by an estate or trust is attributed to any beneficiary with an actuarial interest of 5% or more, to the extent of that interest.

Spouses

An individual is generally treated as owning any stock held by their spouse. The attribution turns off for a given corporation only if all four of these are true for the tax year:⁶

the individual owns no stock in the corporation directly at any time during the year;
the individual is not a director, employee, or manager of the corporation at any time during the year;
no more than 50% of the corporation’s gross income for the year is passive (rents, royalties, dividends, interest, annuities); and
the spouse’s stock is not subject to transfer restrictions favoring the individual or their minor children.

Fail any one, and the spouse’s stock gets attributed.

Parents and Children

A parent is treated as owning any stock held by their children under 21, and a minor child is treated as owning stock held by their parents. There is no ownership floor and no exception.⁶

Attribution among adult children, grandchildren, parents, and grandparents is narrower. An individual is treated as owning a family member’s stock only if that individual already owns more than 50% of the corporation on their own.⁶ Attribution flows toward someone who already controls the corporation; it does not build control from scratch. A parent at 45% does not pick up an adult child’s 20%.

Stock That Doesn’t Count

Some stock is stripped out of the ownership math. Nonvoting stock that is preferred and limited as to dividends, and treasury stock, are excluded for all controlled group types.⁷

For brother-sister testing, additional categories are ignored:

stock held by a tax-exempt employees’ trust for the benefit of that corporation’s employees;
stock held by an employee under conditions that substantially restrict disposal and favor a common owner; and
stock held by a Section 501(c)(3) organization controlled by the corporation, its principal stockholders, or its officers.

Foreign corporations get separate treatment. A foreign corporation not subject to U.S. tax on effectively connected income is an “excluded member,” meaning it can still sit in the ownership chain that establishes the group but is not itself subject to the shared limits imposed on the domestic members.³

What Changes Once You’re a Controlled Group

The IRS treats the group as one employer across a range of provisions. The consequences are not confined to the WOTC.

Work Opportunity Tax Credit

Section 52 aggregates all employees across the group when computing the WOTC.¹ You cannot claim the credit by moving an existing employee from one group entity to another and calling it a new hire. From the IRS’s view, the economic employer never changed.

Retirement Plans

Under Section 414(b) and (c), all employees of every group member are one workforce for coverage and nondiscrimination testing under Sections 401, 410, 411, 415, and 416.² A 401(k) sponsored by one entity must cover a sufficient percentage of the whole group, not just that entity’s employees. A plan offered to 30 people at one company inside a 200-employee group will almost certainly fail minimum coverage.⁸ Failure can disqualify the plan and hit every participant with immediate tax consequences.

Section 179 Expensing

The group shares one Section 179 limit, which is $2,560,000 for 2026 and begins to phase out when property placed in service by the group exceeds $4,090,000.⁹ Two entities cannot each claim the full amount. Allocation among members should be documented in a written apportionment plan.

Research Credit

All members are one taxpayer under Section 41. The group computes a single credit on aggregate qualified research expenses and allocates it to members in proportion to their share of those expenses.¹⁰

Accumulated Earnings Credit

The group shares a single $250,000 accumulated earnings credit, or $150,000 if any member is a personal service corporation, divided among all component members.¹¹

ACA Employer Mandate

The 50-full-time-employee threshold that triggers the ACA employer mandate is measured across the group. Aggregation rules reference Section 414, which uses the same controlled group definitions.¹² A 30-employee business that feels comfortably below the line may sit inside a group of 120 and pull every member into applicable large employer status.

Cafeteria Plans

Section 125 nondiscrimination testing treats the group as a single employer, including for the “simple” cafeteria plan safe harbor available to smaller employers.¹³ A business small enough to qualify on its own may lose the safe harbor once group headcount is added in.

Schedule O and the Apportionment Plan

Every corporation that is a component member must file Schedule O (Form 1120) with its return each year it stays in the group, even with no apportionment plan and no change from the prior year.¹⁴ The schedule identifies the other members and shows how shared items like the Section 179 deduction and accumulated earnings credit are divided.

When members file a consolidated return, the common parent files one Schedule O for the group. If every member of a parent-subsidiary group required to file a U.S. return joins the same consolidated return, no Schedule O is needed. The written apportionment plan itself is signed by an authorized person for each entity and kept in each entity’s records; the IRS directs taxpayers not to attach it to the return.

1
Office of the Law Revision Counsel. 26 USC 52 – Special Rules
2
Office of the Law Revision Counsel. 26 USC 414 – Definitions and Special Rules
3
eCFR. 26 CFR 1.1563-1 – Definition of Controlled Group of Corporations and Component Members and Related Concepts
4
Internal Revenue Service. Controlled and Affiliated Service Groups – Related Employers Phone Forum Presentation
5
Internal Revenue Service. Chapter 7 – Controlled and Affiliated Service Groups
6
Office of the Law Revision Counsel. 26 USC 1563 – Definitions and Special Rules
7
eCFR. 26 CFR 1.1563-2 – Excluded Stock
8
eCFR. 26 CFR 1.410(b)-2 – Minimum Coverage Requirements (After 1993)
9
Internal Revenue Service. Revenue Procedure 2025-32
10
eCFR. 26 CFR 1.41-6 – Aggregation of Expenditures
11
Office of the Law Revision Counsel. 26 USC 1561 – Limitation on Accumulated Earnings Credit in the Case of Certain Controlled Corporations
12
Internal Revenue Service. Determining if an Employer Is an Applicable Large Employer
13
Office of the Law Revision Counsel. 26 USC 125 – Cafeteria Plans
14
Internal Revenue Service. Instructions for Schedule O (Form 1120) – Consent Plan and Apportionment Schedule for a Controlled Group