If you’re self-employed and researching retirement plans, you’ve probably seen several different terms used interchangeably:
Watch: Learn if a self-employed 401k the same as a solo 401k
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Self-Employed 401(k)
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Solo 401(k)
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Solo-k
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Uni-k
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One-Participant 401(k)
So what’s the difference?
The Short Answer: There Is No Difference
All of these terms describe the exact same type of retirement plan.
The IRS officially calls it a One-Participant 401(k) Plan. Financial institutions and providers use various marketing names, but legally and structurally, they are the same plan.
Let’s break it down clearly.
What Is a Solo 401(k)?
A Solo 401(k) (also called a One-Participant 401(k)) is a traditional 401(k) plan designed specifically for:
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Self-employed individuals
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Owner-only businesses
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Business owners with no full-time W-2 employees (other than a spouse)
It is not a new or special type of retirement plan. It follows the same sections of the Internal Revenue Code that govern traditional employer 401(k) plans.
The only difference is who participates.
Why Are There So Many Names?
Over time, providers have created different branding terms:
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Self-Employed 401(k) – emphasizes eligibility
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Solo 401(k) – highlights that only owners participate
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Solo-k / Uni-k – shortened marketing versions
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One-Participant 401(k) – official IRS terminology
Regardless of the name, the structure and rules are the same.
Is It Different From a Regular Employer 401(k)?
Technically, no.
A Solo 401(k) is legally the same type of retirement plan as a traditional employer 401(k). The primary difference is participation.
| Traditional Employer 401(k) | Solo / Self-Employed 401(k) |
|---|---|
| Covers multiple employees | Covers only owner(s) and spouse |
| Subject to nondiscrimination testing | No nondiscrimination testing |
| More administrative complexity | Simpler administration |
| Higher administrative costs | Typically lower costs |
Because there are no non-owner employees, Solo 401(k) plans are exempt from ERISA nondiscrimination testing requirements.
Who Is Eligible?
You qualify for a Solo (Self-Employed) 401(k) if:
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You have earned income from self-employment
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You have no full-time W-2 employees working 1,000+ hours per year
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You (and possibly your spouse) earn compensation from the business
Important Clarifications
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Income must be earned from services performed (not passive income).
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Independent contractors (1099-NEC) are not considered employees for plan eligibility purposes.
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You may exclude employees under age 21.
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Entity type does not matter (sole proprietorship, LLC, S-Corp, C-Corp, partnership) — what matters is that you have self-employment income.
If both spouses work in the business, both can participate in the same Solo 401(k), effectively doubling contribution potential.
Contribution Structure
A Solo 401(k) follows the same contribution rules as any 401(k) plan.
Because you are both the employee and employer, you can contribute in two roles:
Employee Salary Deferral
You can make employee deferral contributions just like in a traditional employer 401(k).
Employer Profit-Sharing Contribution
Your business can also contribute:
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20% of net earnings (sole proprietorship/partnership)
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25% of W-2 wages (S-Corp or C-Corp)
For 2026, the overall contribution limit is $72,000 (higher if eligible for catch-up contributions).
Spouses can each make their own employee and employer contributions if they are compensated by the business.
Advanced Features
A properly designed Solo 401(k) can also allow:
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Mega Backdoor Roth strategy
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Participant loans (up to 50% of balance, max $50,000)
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Rollovers from IRAs and former employer plans
Just like a traditional 401(k), these features depend on how the plan document is drafted.
Distribution Rules
Distribution rules are generally the same as any 401(k):
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Age 59½ for penalty-free withdrawals
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10% early withdrawal penalty if under 59½ (plus taxes)
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Required Minimum Distributions (RMDs) beginning at age 73
Key RMD Difference
If you participate in a traditional employer 401(k) and are still working there, you may delay RMDs.
With a Solo 401(k), since you are the business owner, you must begin RMDs at age 73 — you cannot delay them based on employment status.
Administrative Requirements
A Solo 401(k) must:
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Be established using qualified plan documents
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File Form 5500-EZ once assets exceed $250,000
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Follow standard 401(k) compliance rules
Despite these requirements, administration is generally much simpler than a full employer 401(k).
Why the Confusion?
Many people assume a Solo 401(k) is a separate or special retirement account.
It’s not.
The IRS does not recognize “Solo 401(k)” as a distinct category. It is simply a one-participant version of a traditional 401(k) plan.
Financial institutions use different names for marketing purposes, but legally the structure is identical.
The Bottom Line
There is no technical difference between:
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Self-Employed 401(k)
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Solo 401(k)
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Solo-k
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Uni-k
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One-Participant 401(k)
They all describe the same retirement plan — a traditional 401(k) designed for owner-only businesses.
If you are self-employed and want:
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Higher contribution limits than an IRA
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The ability to contribute as both employee and employer
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Access to the Mega Backdoor Roth strategy
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Loan flexibility
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Lower administrative complexity
Then a Solo (Self-Employed) 401(k) may be one of the most powerful retirement tools available to you.
