What Happens to a Solo 401(k) When I Hire My First Employee?
A focused answer for business owners and rental-property owners.
The direct answer
Hiring requires a plan-eligibility review. A one-participant 401(k) generally covers an owner with no employees, or the owner and spouse; when an employee becomes eligible, the plan’s obligations can change.
How to evaluate your situation
Do not assume that every new hire enters the plan immediately or that labeling someone part time avoids coverage. Eligibility can depend on age, service, hours and the plan document, including applicable long-term part-time rules. The employer should provide the administrator with a complete census, hiring dates and service records. Review related businesses and ownership relationships where relevant rather than considering only the entity that pays the owner. A plan that must cover eligible employees may require additional administration and testing. Decide how to transition before the eligibility date, and coordinate notices and contributions with the administrator. Keeping the old “solo” label does not override coverage requirements.
Hypothetical example
An owner hires an assistant and continues the existing owner-only plan. The administrator checks the assistant’s age, hours, service and the plan’s terms. The employer does not wait until year-end to ask whether coverage should already have begun.
Records to gather
- Employee census
- birth dates
- hire dates
- hours
- related-entity ownership
- plan document
- eligibility calculations
Related question
Does hiring my spouse always end owner-only plan treatment?
An owner-and-spouse plan can still be a one-participant arrangement under IRS guidance. Other eligible employees and the full plan facts require a separate review.
Source and next step
Updated September 30, 2026. This general federal tax discussion does not decide an individual filing position. Apply the current instructions for the actual tax year and your complete facts.
Review the related AE service and bring the listed records to a discovery call.
AE engagement pricing
$7,800 standard advisory engagement. No required recurring annual planning fee. Two $3,900 payments, 30 days apart. Returns, amendments, cost segregation and additional services are separately scoped. See published pricing for the service you need.
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