IRS Controlled Group Rules: Types, Attribution, and Penalties

The IRS controlled group rules treat related businesses under common ownership as a single employer for retirement plan compliance, ACA obligations, certain deduction limits, and other federal tax purposes. The core authority sits in Internal Revenue Code Sections 414(b) and 414(c), which pull in the ownership definitions of Section 1563(a).¹ If your businesses meet the thresholds, you cannot offer a generous 401(k) at one entity while excluding the workforce of another, and you cannot claim per-entity dollar limits that Congress wrote as per-group. Miss the aggregation and the consequences follow every entity, not just the one where the mistake happened.

The Three Types of Controlled Groups

Section 1563(a) defines three structural relationships: parent-subsidiary, brother-sister, and combined. Each turns on specific ownership percentages measured by voting power or total stock value.²

Parent-Subsidiary

One corporation owns at least 80 percent of the voting power or total value of another corporation’s stock. The chain can extend downward through multiple tiers so long as each link meets the 80 percent threshold. If Company A owns 90 percent of B and B owns 85 percent of C, all three form a single parent-subsidiary group. The threshold is tested at each link, not by multiplying stakes together.

Brother-Sister

Five or fewer common owners (individuals, estates, or trusts) own more than 50 percent of each corporation, counting only the identical ownership each person holds across every entity. Identical ownership is the smallest stake a particular owner holds in any entity being compared.

Take Owner X, who holds 60 percent of Company D and 40 percent of Company E: X’s identical ownership is 40 percent. Owner Y holds 20 percent of D and 30 percent of E, so Y’s identical ownership is 20 percent. Combined identical ownership is 60 percent, which clears the 50 percent threshold. Companies D and E are a brother-sister group.

This is the test that surprises people. You do not need to own a majority of both companies outright. Two owners with moderate overlapping stakes can trip it easily.

Combined

Three or more organizations belong to both a parent-subsidiary group and a brother-sister group, with at least one entity acting as the common parent of the vertical chain while also being a member of the brother-sister group. Combined groups tend to appear in family business structures where vertical and horizontal ownership overlap.

Constructive Ownership: The Stock You’re Treated as Owning

Direct ownership rarely tells the full story. Attribution rules treat stock held by one person or entity as owned by a related person or entity, and they exist specifically to prevent owners from scattering shares across enough hands to duck the thresholds.

Family Attribution

Ownership is attributed between spouses, parents, children (including adopted children), and grandparents. Minor children under 21 and their parents have automatic two-way attribution. For adult children 21 or older, attribution from parent to child only kicks in if the child already owns more than 50 percent of the corporation.¹

A narrow spousal exception applies in brother-sister analyses. A spouse’s stock is not attributed to the other spouse if all four of these are true: the non-owning spouse has no direct ownership in the business, does not participate in management, the corporation earns no more than 50 percent of gross income from passive sources, and the stock is subject to transfer restrictions. Most married couples running related businesses will not qualify.

Option Attribution

If you hold an option to acquire stock, you are treated as already owning it, whether or not the option is currently exercisable. An individual who owns 75 percent of a company and holds an option on another 10 percent is treated as owning 85 percent, clearing the 80 percent parent-subsidiary threshold and potentially creating a controlled group that did not appear to exist on paper.

Entity Attribution

Ownership flows through corporations, partnerships, trusts, and estates, with different rules for each:

Stock held by a corporation is attributed proportionally to any shareholder owning at least 5 percent of the corporation’s value, and stock owned by a 5-percent-or-greater shareholder is attributed back to the corporation in proportion to their stake.³
Stock held by a partnership is attributed proportionally to every partner, with no minimum threshold, and stock owned by any partner is attributed to the partnership.
Stock held by an estate or trust is attributed proportionally to beneficiaries based on their actuarial interest, and stock owned by a beneficiary is attributed back to the estate or trust unless the interest is remote or contingent.

Attribution stacks. A father who directly owns 40 percent of Company X and holds an option on another 10 percent is treated as owning 50 percent. Because his constructive ownership hits 50 percent, his adult son’s stock in Company Y can be attributed to him, potentially linking X and Y as a brother-sister group. No single step alone creates the group. Together they do.

What Changes for Retirement Plans

Once a controlled group exists, every member is treated as a single employer for retirement plan testing and administration.¹ Getting this wrong can disqualify a plan and trigger taxes on every participant’s balance.

Coverage Testing

Any qualified plan must satisfy the minimum coverage requirements of IRC Section 410(b) by looking at employees across the entire group. The most commonly used test requires the plan’s coverage rate for non-highly compensated employees to equal at least 70 percent of the coverage rate for highly compensated employees.⁴ For 2026, an HCE is generally someone who earned more than $160,000 in the prior year.⁵

If one entity sponsors a 401(k) but a sister entity employs 200 lower-wage workers who are excluded, all 200 count as NHCEs not benefiting under the plan. The math that looked fine at one entity collapses once the whole group is measured. This is the single most common failure when controlled group status goes unrecognized. A separate line of business election under IRC Section 414(r) can sometimes carve out genuinely distinct operations (each line needs at least 50 employees), but the requirements are strict enough that most small groups cannot use it.⁶

Nondiscrimination Testing

The ADP test for 401(k) deferrals and the ACP test for matching contributions run across the entire controlled group. Every HCE in every entity is measured against every NHCE in every entity. A plan that easily passes ADP inside a single professional services firm can fail once a commonly owned staffing company’s employees enter the calculation.

Contribution and Benefit Limits

For 2026, the maximum annual addition to a defined contribution plan (employer contributions plus employee deferrals plus forfeitures) is $72,000 per participant.⁵ That limit applies across the group, not per entity. An employee who works for two group members cannot receive $72,000 from each. The entities must coordinate, and if they don’t, the excess triggers additional taxes for the participant and potential plan disqualification.

Top-Heavy Rules

A plan is top-heavy when key employees hold more than 60 percent of total account balances or accrued benefits, measured across the whole controlled group.⁷ For 2026, a key employee is generally an officer earning more than $235,000 or certain owners.⁵ A top-heavy plan must provide a minimum contribution of at least 3 percent of compensation to all non-key employees. Where the group employs many non-key workers, that minimum contribution obligation can be expensive.

Form 5500

For Form 5500 reporting, a controlled group is one employer. A plan sponsored by a member files as a single-employer plan, not a multiple-employer plan, even when several legal entities participate.⁸

ACA Employer Mandate

Controlled group status determines whether you are an Applicable Large Employer under the ACA. An ALE averaged at least 50 full-time employees (including full-time equivalents) during the prior calendar year, and all employees across every group member count toward that headcount.⁹

This regularly catches multi-entity owners. A restaurant group with four entities of 15 full-time workers each has 60 employees in aggregate and is an ALE, even though no single entity hits 50. Once you cross the threshold, every entity must offer minimum essential coverage to at least 95 percent of its full-time employees. For 2026, failing to offer coverage at all carries a $3,340 penalty per full-time employee (after subtracting the first 30), and offering coverage that is unaffordable or insufficient carries a $5,010 penalty per employee who receives subsidized coverage through an exchange. Each ALE member must file Forms 1094-C and 1095-C annually.¹⁰

Section 179 Applies to the Whole Group

Section 179 lets a business expense the full cost of qualifying equipment in the year it is placed in service. The dollar cap is per group, not per entity. For 2026, the maximum Section 179 deduction is $2,560,000, and it phases out once total qualifying property placed in service across all group members exceeds $4,090,000.¹¹ Above $6,650,000 the deduction disappears entirely. A controlled group that buys equipment through multiple entities cannot claim a separate $2,560,000 deduction at each one.

Employment Taxes and the Common Paymaster

For FICA and FUTA, each entity is generally its own employer, and the FUTA tax applies to the first $7,000 of each employee’s annual wages per employer.¹² When an employee works concurrently for multiple group members, the common paymaster mechanism prevents double-counting the wage base. A designated member disburses compensation on behalf of all entities that concurrently employ the worker, and a single FICA and FUTA wage base applies to the combined wages.¹³ Skip the arrangement and each entity applies a separate wage base, which usually means overpaying.

Affiliated Service Groups: The Rule for Service Businesses

Clearing the controlled group thresholds does not always end the analysis. IRC Section 414(m) creates a parallel aggregation rule for service organizations, and when an affiliated service group exists, its members are treated as a single employer for the same retirement plan and benefit requirements.¹⁴

Two main configurations exist. In one, a service organization is a shareholder or partner in another and regularly performs services for or alongside it. In the other, a separate organization performs services historically done by employees in that field, and at least 10 percent of that organization’s ownership is held by HCEs of the first. A third variant covers management companies: if one company’s principal business is performing management functions on a regular, continuing basis for another organization, both form an ASG. That catches the common arrangement where a professional practice sets up a separate entity to handle billing, staffing, and administration.

The IRS scrutinizes medical practices, law firms, accounting groups, and engineering firms that split operations across entities. If your structure resembles any of these patterns, a formal ASG analysis belongs in your compliance routine even when the ownership math falls short of controlled group thresholds.

Penalties, PBGC Liability, and Correction

The most immediate risk from missed aggregation is plan disqualification. When a plan fails coverage, nondiscrimination, or contribution limits because a sponsor did not account for related entities, participants can be taxed on their entire account balances and the employer loses its deduction for contributions.

Joint and Several Liability for Pensions

Under ERISA, all members of a controlled group are jointly and severally liable for certain pension obligations. If one member sponsors a defined benefit plan that terminates with insufficient assets, the Pension Benefit Guaranty Corporation can pursue any group member for the full termination liability under ERISA Section 4062.¹⁵ The same principle governs withdrawal liability in multiemployer plans. An otherwise healthy subsidiary can be on the hook for a sibling’s underfunded pension, a risk that often goes unexamined during acquisitions and reorganizations.

EPCRS: The Three Correction Paths

If you discover a compliance failure tied to overlooked aggregation, the IRS Employee Plans Compliance Resolution System offers three routes:¹⁶

The Self-Correction Program handles certain operational failures without contacting the IRS or paying a fee, and it works best for failures caught and fixed quickly.
The Voluntary Correction Program requires a submission through Pay.gov using Form 8950, a proposed correction method, and a user fee. Once the IRS issues a compliance statement, the sponsor has 150 days to complete corrections.
The Audit Closing Agreement Program applies when the failure surfaces during an IRS audit. Sanctions are negotiated and are always at least as high as VCP fees.

Early discovery matters. A coverage failure fixed through SCP might cost nothing beyond the makeup contributions owed to excluded employees. The same failure caught on audit can produce a sanction that dwarfs what VCP would have cost.

Mergers and the Transition Period

When companies merge or are acquired, the controlled group changes overnight, and an entity that joins a new group would otherwise have to pass coverage tests with a workforce it did not have the day before. A transition rule prevents that. Coverage requirements are treated as met during the transition period if the plan met coverage immediately before the change and the plan’s coverage is not significantly changed during the period (other than the change in group composition itself). The transition period begins on the date of the ownership change and ends on the last day of the first plan year beginning after that date.¹⁷

For a calendar-year plan, a July acquisition gives you roughly 18 months before the enlarged group must pass aggregated coverage testing. A December acquisition gives you about 12. Use the window to redesign plan eligibility or restructure so the plan can pass once the transition expires. Letting it lapse and hoping the tests come out right is how controlled group problems become plan disqualification proceedings.

1
Office of the Law Revision Counsel. 26 USC 414 – Definitions and Special Rules
2
Office of the Law Revision Counsel. 26 US Code 1563 – Definitions and Special Rules
3
Internal Revenue Service. Chapter 7 Controlled and Affiliated Service Groups
4
Office of the Law Revision Counsel. 26 USC 410 – Minimum Participation Standards
5
Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted
6
eCFR. Qualified Separate Line of Business – Fifty-Employee and Notice Requirements
7
Office of the Law Revision Counsel. 26 USC 416 – Special Rules for Top-Heavy Plans
8
Department of Labor. 2025 Instructions for Form 5500 Annual Return/Report of Employee Benefit Plan
9
Internal Revenue Service. Determining if an Employer is an Applicable Large Employer
10
Internal Revenue Service. Information Reporting by Applicable Large Employers
11
Internal Revenue Service. Rev Proc 2025-32 – Election to Expense Certain Depreciable Assets
12
Internal Revenue Service. Topic No 759 – Form 940 Employers Annual Federal Unemployment FUTA Tax Return
13
Internal Revenue Service. Common Paymaster
14
Office of the Law Revision Counsel. 26 US Code 414 – Definitions and Special Rules
15
Pension Benefit Guaranty Corporation. OGC Opinion Letter 86-8 – Controlled Group Liability
16
Internal Revenue Service. EPCRS Overview
17
Cornell Law School – Legal Information Institute. Definition – Transition Period from 26 USC 410(b)(6)