Solo 401(k) eligibility checker
A Solo 401(k) works only if no eligible common-law employee exists anywhere in your controlled group of businesses, not just at the one business sponsoring the plan. The screener below asks four questions and returns one of three results: likely eligible, likely not eligible because a controlled group or its employees are in the way, or a gray area that needs a professional review. It runs entirely in your browser and checks the same two triggers explained on our full controlled-group guide: 80%-or-more common ownership (IRC 414(b)/(c)) and the affiliated-service-group rule (IRC 414(m)), which has no ownership threshold at all.
Solo 401(k) eligibility checker
Answer based on the business you want the Solo 401(k) for. Nothing you enter here is saved or sent anywhere; the logic runs entirely in your browser.
You likely CAN run a Solo 401(k)
No eligible employee at your own business, no 80%+ common ownership of another business, and no close working relationship with another business in the same field. None of the combination tests, controlled-group or affiliated-service-group, have anything to attach to. This is the clean, owner-only case a Solo 401(k) is built for.
Zero controlled-group ownership and zero affiliated-service-group ties means neither IRC 414(b)/(c) nor 414(m) has a basis to combine your businesses.
This is a screen, not a legal determination. Nothing here changed the ownership or employee facts you entered, so re-run it if anything about your businesses changes.
Logic source: IRC 414(b), 414(c), 414(m), 1563; IRS, "One-Participant 401(k) Plans"; IRS Employee Plans, "Controlled and Affiliated Service Groups" training deck. This tool is a screen, not tax, legal, or investment advice, and it does not replace a facts-and-circumstances review from a TPA or ERISA attorney.
Why does owning more than one business complicate a "solo" plan?
A Solo 401(k), also called a one-participant 401(k), is only allowed when the business sponsoring it has no eligible common-law employee besides the owner and a working spouse. The complication is that the IRS does not evaluate that rule one LLC at a time. Two federal tests, the controlled group rules (IRC 414(b) and 414(c)) and the affiliated service group rule (IRC 414(m)), can pull two or more of your businesses together and treat them as a single employer for this purpose, regardless of separate EINs, bank accounts, or branding. If any business inside that combined group has an eligible employee, the whole group generally has to offer that person coverage, and a plan that only covers the owner stops working.
That is the entire reason this screener exists: the question is never just "does my business have employees?" It is "does my business, or any business commonly owned or closely affiliated with it, have an eligible employee?"
What is the 80% controlled-group test, in plain words?
If you (counting a spouse's or minor child's ownership with yours) own 80% or more of another active business, the two are generally a controlled group under IRC 414(b) (corporations) or 414(c) (any other business form, including partnerships, sole proprietorships, and LLCs). Once that threshold is crossed, the IRS treats both businesses as one employer for retirement-plan purposes: eligibility and coverage testing (IRC 410(a) and (b)), nondiscrimination testing (IRC 401(a)(4)), top-heavy testing (IRC 416), and the overall contribution limit (IRC 415(c)) all apply to the group, not to each entity in isolation.
The trap most people miss is spousal attribution. Under IRC 1563(e), a spouse's ownership is generally attributed to the other spouse in full, so two businesses owned separately by each spouse are very often a controlled group by default, not two unrelated companies. A narrow exception exists, but it requires the non-owning spouse to have zero management role, the business to earn 50% or less of its income from passive sources, and no restriction on the spouse's right to dispose of the interest. Most actively-run small businesses fail that exception on the passive-income prong alone. The full attribution rules, including parent-child attribution, are worked through on our Solo 401(k) with multiple businesses guide.
What is the affiliated-service-group trap, and why does it not need any ownership at all?
The affiliated-service-group rule (IRC 414(m)) exists specifically for service businesses, law, medical, consulting, accounting, bookkeeping, and similar practices, that split work across entities without necessarily sharing ownership. Unlike the controlled-group tests, it has no fixed ownership percentage. Two structures matter: an "A-Org" or "B-Org" that owns a stake in, or regularly performs services with or for, a "First Service Organization," and a "management group," where a separate company's main job is performing management or back-office functions for another business, with no ownership tie required whatsoever.
This is why question 4 in the screener above does not ask about ownership percentage. A 10 to 20% stake in a referral partner's practice, or a "separate" management LLC that runs your other business's payroll and scheduling, can still combine the two under this rule even at 0% shared ownership. The IRS's own training materials describe these calls as facts-and-circumstances, which is exactly why a "yes" here returns a gray-area result instead of a hard CAN or CANNOT.
When do I actually have to cover employees at another business?
Only when the combination tests pull the businesses together in the first place. If your businesses fail both the controlled-group tests (below 80% common ownership, with attribution counted in) and the affiliated-service-group test (no A-Org/B-Org or management-company relationship), each one is evaluated on its own, and an unrelated business's employees are not your problem. Once either test does combine them, the minimum-coverage rule (IRC 410(b)) applies to the group as a single employer: any common-law employee elsewhere in the group who has met the plan's age-and-service eligibility (typically age 21 and one year of service) generally must be offered a path into the plan, and the arrangement has to pass nondiscrimination testing under IRC 401(a)(4).
The one clean safe harbor, regardless of how the ownership is structured, is having zero eligible employees anywhere in the entire group. Multiple owner-only businesses, no matter how they are commonly owned, have nothing for the coverage rule to reach. For what this actually does to a solo plan's dollar limits once a controlled group does have staff, see the worked example on Solo 401(k) with multiple businesses, which runs a $72,000 2026 combined-limit case through the numbers.
What does a CAN, CANNOT, or gray-area result actually mean?
The screener above collapses to one of three outcomes. The table below shows what drives each one and what to do next.
| Result | What triggers it | What to do |
|---|---|---|
| CAN: likely eligible for a Solo 401(k) | No eligible employee at your business, no 80%+ commonly-owned business with an eligible employee, and no affiliated-service-group relationship | Proceed with a one-participant plan design. Re-check if you hire anyone or take on a new ownership stake or referral relationship. |
| CANNOT: likely not eligible as a solo plan | An eligible employee exists at your own business, or at a business that is 80%+ commonly owned with yours | You cannot run a solo-only plan. Cover the eligible employee(s) under the plan, or get a plan design (such as a safe-harbor formula) reviewed by a TPA or ERISA attorney before funding anything. |
| Gray area: common ownership or affiliated-service-group rules may apply | Under 80% ownership, but a stake in or close working relationship with another business in the same service field | Do not assume you are clear on ownership percentage alone. Get an affiliated-service-group determination from a TPA or ERISA attorney; this is a facts-and-circumstances call, not a bright-line one. |
Source: IRC 414(b), 414(c), 414(m), 1563; IRS Employee Plans, "Controlled and Affiliated Service Groups" training deck; IRS, "One-Participant 401(k) Plans."
How does this screener work, and what does it not check?
The tool asks four yes/no questions and follows the same branching the IRS training materials describe: first, whether your own business already has an eligible employee (that alone ends the analysis); then, if you own 80% or more of another business, whether that business has an eligible employee; and if you are under that 80% threshold, whether you have any ownership stake in, or close working relationship with, another business in the same or a related service field. It does not run the numeric contribution math (see the Solo 401(k) contribution calculator for that), it does not evaluate parent-child attribution or partial-ownership combinations across three or more entities, and it does not replace an actual affiliated-service-group opinion. Anyone with an ownership structure that is not obviously simple, a spouse's separate business, a referral partner, a management company, or a minority stake, should treat a gray-area or CANNOT result as the floor of the analysis, not the ceiling.
The flat truth
Owning more than one business does not automatically block a Solo 401(k). Having an eligible employee anywhere in your commonly-owned or affiliated group of businesses is what blocks it. This screener exists to give you a same-day read on which side of that line you are probably on, but it cannot see your cap table, your family's other ownership interests, or the actual working relationship between your businesses in the level of detail an IRS examiner or a TPA would. Treat a CAN result as a reasonable starting point, and treat a CANNOT or gray-area result as a clear signal to stop and get a real determination before you fund anything. For the full rules behind every question above, including the family attribution details and the affiliated-service-group A-Org/B-Org and management-group structures, see Solo 401(k) with multiple businesses.
Related reading: what a Solo 401(k) is and who qualifies for the eligibility basics behind this screener, and Solo 401(k) contribution limits for 2026 for the dollar figures referenced above.
Sources
- Solo 401(k) eligibility and the "no common-law employees" rule: IRS, "One-Participant 401(k) Plans".
- Controlled-group definitions, thresholds, attribution rules, and affiliated-service-group A-Org/B-Org and management-group tests: IRS Employee Plans, "Controlled and Affiliated Service Groups" phone forum training deck.
- Examination-level guidance on controlled and affiliated service groups: IRS Employee Plans Chapter 7, "Controlled and affiliated service groups".
- 2026 dollar limits referenced in the linked worked example: IRS Notice 2025-67, "2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living".
- Statutory basis: IRC 414(b), 414(c), 414(m), and 1563 (and Treasury regulation 1.414(c)-2 on the definition of "organization"), as summarized and applied in the IRS training materials above.