Can I Have a Solo 401(k) If I Have Employees?

You can keep a Solo 401k with employees only in narrow circumstances: the plan stays a one-participant arrangement as long as the only people covered are you and, if applicable, your spouse. The moment any other worker meets the federal age and hours thresholds for plan participation, your Solo 401k no longer qualifies, and you have to convert it to a standard 401k or terminate it. Several categories of workers don’t count toward that threshold, though, and knowing which ones lets you grow the business without losing the plan.

When an Employee Ends Your Solo Status

Federal law sets two tests that decide whether a worker is eligible for your retirement plan: age and hours. A plan cannot exclude an employee who has reached age 21 and completed one year of service, meaning a 12-month period in which they worked at least 1,000 hours.1Office of the Law Revision Counsel. 26 USC 410 – Minimum Participation Standards Once any non-spouse worker crosses both, your plan stops meeting the one-participant definition.2Internal Revenue Service. One-Participant 401(k) Plans

The reason is nondiscrimination law: you can’t keep a tax-qualified plan for yourself while excluding a worker who qualifies. Leaving an eligible employee out can cost the plan its tax-exempt status entirely, which means back taxes and possible penalties on contributions you’ve already made.

The Long-Term Part-Time Rule

The 1,000-hour line used to be the whole story. It isn’t anymore. Under SECURE 2.0, a part-time employee who works at least 500 hours in each of two consecutive 12-month periods becomes eligible to make elective deferrals, even if they never hit 1,000 hours in any single year. The rule took effect for plan years beginning after December 31, 2024.3Internal Revenue Service. Notice 2024-73

So if you hired a part-time assistant in 2024 who logged 550 hours that year and another 550 in 2025, that worker became eligible to defer into a plan on January 1, 2026. Your Solo 401k can’t stay a one-participant plan at that point unless the worker fits an excludable category.

One piece of the rule works in your favor. You are not required to make employer matching or profit-sharing contributions to an employee who becomes eligible solely through the long-term part-time rule.3Internal Revenue Service. Notice 2024-73 The employee still has to meet the plan’s age requirement. But because they can now defer their own pay, the plan is no longer owner-only, and you’ll need to move to a standard 401k structure.

Workers Who Don’t Trigger a Conversion

Not every person who does work for your business counts as an eligible employee. A few categories let you keep the Solo 401k.

Independent Contractors

Independent contractors — 1099 workers — are self-employed. They are not your employees for retirement plan purposes and have no effect on your Solo 401k. The IRS looks at three categories of evidence when deciding whether someone is genuinely a contractor: behavioral control over how the work is done, financial control over the business side of the arrangement, and the nature of the overall relationship.4Internal Revenue Service. Independent Contractor or Employee (Publication 1779)

If you dictate when, where, and how a worker performs tasks, supply their tools, or treat the relationship as permanent and exclusive, the IRS can reclassify that person as a common-law employee. Reclassification carries back taxes, penalties, and the possibility that your Solo 401k is retroactively disqualified. Keep written contracts that define the scope of work and the independent nature of the arrangement, and make sure the actual working relationship matches the contract.

Employees Who Haven’t Hit the Thresholds

Workers under age 21, or those who haven’t completed 1,000 hours in a 12-month period, aren’t yet eligible under the standard rule.1Office of the Law Revision Counsel. 26 USC 410 – Minimum Participation Standards A seasonal worker who puts in 800 hours over the summer and doesn’t come back won’t affect your plan. Watch the low-hour cases carefully, though. Anyone averaging around 10 hours per week can hit the 500-hour mark that starts the two-year long-term part-time clock, so track hours for every worker, not just full-timers.

Other Excludable Groups

Federal law lets you exclude a few additional groups. Employees covered by a collective bargaining agreement that addresses retirement benefits through separate arrangements generally don’t need to be in your plan. Nonresident aliens who receive no U.S.-source income from your business can also be excluded. Neither situation comes up often for Solo 401k holders, but they can apply if you have unionized staff or international operations.

Employing Your Spouse

Your spouse is the one person you can employ without ending the Solo 401k. A spouse who works in the business, receives a W-2 salary, and performs legitimate services can participate in the plan as a second participant while it keeps its one-participant classification.2Internal Revenue Service. One-Participant 401(k) Plans Both spouses can make elective deferrals and receive employer profit-sharing contributions, effectively doubling the household’s tax-advantaged savings.

The spouse’s pay has to be reasonable for the work actually performed. Inflating a spouse’s salary just to maximize retirement contributions can draw IRS scrutiny and lead to adjustments of both the business’s deductions and the individual’s taxable income.5Internal Revenue Service. Paying Yourself When the salary reflects genuine duties, the plan stays exempt from the nondiscrimination testing that applies to larger plans.

The Multi-Business Trap

Owning more than one business can end your Solo 401k eligibility in a way that isn’t obvious. If the IRS treats your businesses as a controlled group or an affiliated service group, employees across every entity are counted together for retirement plan purposes.6Office of the Law Revision Counsel. 26 USC 414 – Definitions and Special Rules Employees at one business can disqualify the Solo 401k you maintain at another.

The most common triggers are:

Family attribution rules add another layer. Ownership held by your spouse, children, or parents can be treated as yours (and vice versa) when the IRS decides whether a controlled group exists. Stock owned by a minor child, for example, is generally attributed to the parent.8Internal Revenue Service. Controlled and Affiliated Service Groups – IRS Phone Forum Presentation If you run a Solo 401k through a consulting firm while your spouse owns a separate business with employees, have a tax professional look at whether the two together form a controlled group.

What to Do When an Employee Becomes Eligible

When a worker qualifies and the plan can’t remain solo, you have two paths: amend the existing plan to cover the new participants, or terminate the Solo 401k and start a new plan. Most owners amend, because it preserves the existing account and avoids a taxable distribution.

Amending generally means:

  • Updating plan documents. Your provider will prepare amended adoption agreements and plan language reflecting multiple participants.
  • Distributing a Summary Plan Description. Every eligible employee has to receive a written explanation of the plan’s terms, including eligibility, vesting, and contribution formulas.
  • Meeting amendment deadlines. Discretionary amendments generally must be adopted by the end of the plan year in which the change takes effect.9Internal Revenue Service. 401(k) Plan Fix-It Guide – You Haven’t Updated Your Plan Document

Once non-owner employees are in the plan, the administrative load jumps. You’ll face annual nondiscrimination testing (the Actual Deferral Percentage and Actual Contribution Percentage tests) to keep the plan from disproportionately benefiting highly compensated owners. Annual reporting shifts from Form 5500-EZ to a full Form 5500 filed electronically.10Internal Revenue Service. Instructions for Form 5500-EZ

Safe Harbor as an Alternative

If you’d rather skip the nondiscrimination testing, look at a Safe Harbor 401k design. A Safe Harbor plan is exempt from ADP and ACP testing as long as you commit to a minimum employer contribution for every eligible employee.11Internal Revenue Service. Compensation Definition in Safe Harbor 401(k) Plans The most common formulas are a dollar-for-dollar match on the first 3 percent of pay plus a 50-cent match on the next 2 percent, or a flat 3 percent nonelective contribution to every eligible employee regardless of whether they defer. You trade guaranteed employer cost for the certainty of passing the tests.

Cost of the New Plan

Standard 401k plans usually need a third-party administrator to handle compliance testing, filings, and recordkeeping. Setup fees run from a few hundred to a few thousand dollars, with ongoing annual administration fees and often per-participant charges. These costs are deductible business expenses, and the SECURE 2.0 Act provides a tax credit for small employers covering up to $5,000 per year for the first three years of a new plan, which can offset much of the startup expense for businesses with 50 or fewer employees.

Fixing a Missed Eligibility

If you realize you should have included an employee but didn’t, the IRS provides a correction framework called the Employee Plans Compliance Resolution System. Which path you use depends on how serious the error is and how quickly you catch it.

  • Self-Correction Program (SCP): for minor errors, you correct the mistake yourself with no application or fee. Even significant errors can be self-corrected if you act before the end of the third plan year after the failure.12Internal Revenue Service. Correcting Plan Errors – Self-Correction Program (SCP) General Description
  • Voluntary Correction Program (VCP): for errors you can’t self-correct, you submit a formal application with a proposed correction and a user fee. For 2026, fees range from $2,000 for plans with up to $500,000 in assets to $4,000 for plans with more than $10 million in assets.13Internal Revenue Service. Voluntary Correction Program (VCP) Fees

Correction usually means making the contributions the employee would have received, plus lost earnings on those amounts. Catching the problem early keeps costs down and protects the plan’s tax-qualified status. Review your payroll records at least once a year to see whether any worker’s hours have crossed an eligibility line. The cost of that hour is far less than the cost of a retroactive correction, or plan disqualification.