What Is a Solo 401(k) and Should You Get One?
A Solo 401(k) can be one of the most powerful retirement plans for self-employed owners with no employees. Learn how it works, who qualifies, and what to consider before opening one.
If you’re self-employed, run a side business, or own a small company with no employees, you’ve probably heard that a Solo 401(k) (also called an “individual 401(k)” or “one-participant 401(k)”) can allow high retirement contributions with relatively flexible features. But it’s not the right fit for every business, and it comes with real administrative responsibilities.
Below is a clear, practical guide to what a Solo 401(k) is, who can use it, and how to decide whether you should get one.
What is a Solo 401(k)?
A Solo 401(k) is a 401(k) plan designed for a business owner with no common-law employees (other than a spouse). It works much like a traditional employer-sponsored 401(k), but it’s built for a “one-participant” situation.
With a Solo 401(k), you can often contribute in two roles:
Employee (you defer part of your pay into the plan)
Employer (your business makes an employer contribution)
This “two-hat” structure is a key reason Solo 401(k)s can allow larger contributions than some other small-business retirement options, depending on your income and business type.
The IRS provides an overview of one-participant 401(k) plans here: IRS guidance on one-participant (Solo) 401(k) plans.
Who qualifies for a Solo 401(k)?
You generally qualify if:
You have self-employment income (sole proprietor, partnership, LLC, or corporation), and
You have no eligible common-law employees working for your business (a spouse can typically participate)
Important nuance: “No employees” doesn’t always mean “no help.” Many owners use independent contractors. But if someone is truly an employee under IRS/DOL rules, they can trigger the need to include them in the plan—meaning it may no longer be a Solo 401(k). If you’re unsure, it can be worth consulting an ERISA attorney or a qualified advisor.
If you expect to hire employees soon, you may want to think ahead about whether you’ll transition to a traditional plan later with help from retirement plan providers or a specialist advisor.
Solo 401(k) vs. SEP IRA vs. SIMPLE IRA (plain-English comparison)
Many owners consider a Solo 401(k) alongside SEP and SIMPLE IRAs. Here’s a practical comparison:
Solo 401(k): Often supports higher contributions at certain income levels because you can contribute as employee + employer. May allow Roth contributions (depending on the plan document) and participant loans (if the plan allows). More paperwork than an IRA.
SEP IRA: Typically easy to set up and maintain. Contributions are employer-only. If you have eligible employees, you generally must contribute for them too.
SIMPLE IRA: Designed for small employers with employees. Lower contribution limits than a 401(k), but simpler administration than a full 401(k).
Choosing among these often comes down to (1) how much you want to contribute, (2) whether you’ll have employees, and (3) how much administration you’re willing to take on.
Pros of a Solo 401(k)
A Solo 401(k), like a small business 401(k) can be a strong fit if you want meaningful tax-advantaged savings and you don’t want to be boxed into employer-only contributions.
Potentially higher contributions because you may contribute as both employee and employer.
Tax flexibility (traditional pre-tax and, if your plan allows, Roth contributions).
Loans may be available if the plan document permits participant loans (not all do).
Spouse participation can significantly increase household retirement savings if your spouse works in the business.
Cons and responsibilities (what people overlook)
The biggest downside is that a Solo 401(k) is still a qualified retirement plan—meaning there are rules to follow. Common responsibilities include:
Plan document maintenance: Your plan must be established and operated according to written terms.
Ongoing compliance: You must follow contribution rules, eligibility rules, and distribution rules.
Annual reporting once the plan is large enough: When plan assets reach certain thresholds, you may need to file an annual return (commonly Form 5500-EZ for Solo 401(k)s). If you’re not familiar with reporting, see our guide: What is a Form 5500?
Late or missed filings can create headaches and potential penalties. For broader context on why timeliness matters, see: The High Cost of Non-Compliance: Penalties for Late or Rejected Form 5500 Audits.
For official information on Form 5500 filings, you can also reference the U.S. Department of Labor’s Form 5500 resources: EBSA Form 5500 fact sheet.
Do Solo 401(k)s require an audit?
Most Solo 401(k)s do not require an annual independent audit because the audit requirement generally applies to plans with 100+ eligible participants (with some nuances). A true one-participant plan is typically far below that threshold.
That said, if your business grows and you add employees and expand the plan, audit requirements could become relevant. If you ever transition into a plan that needs an audit, these resources can help:
401(k) auditors and all auditors directories if you need to compare firms
Should you get a Solo 401(k)? A simple decision checklist
A Solo 401(k) is often worth considering if most of the following are true:
You have self-employment income and want to maximize retirement savings.
You have no employees (other than a spouse), and don’t expect to hire soon.
You want the option of Roth contributions and/or plan loans (if your plan supports them).
You’re comfortable with a bit more administration than an IRA.
You may want a different solution if:
You expect to hire eligible employees soon (a SEP, SIMPLE, or full 401(k) strategy may fit better).
You want the absolute simplest ongoing maintenance (an IRA-based plan might be easier).
What else should you put in place with a Solo 401(k)?
Even when you’re the only participant, it’s smart to think about your broader compliance and fiduciary “toolkit.” Depending on your setup, you may also need:
Help selecting and monitoring investments (especially if you want a more formal process). Consider working with a specialist from our 401(k) financial advisors directory and review our guide: How To Hire A Retirement Plan Advisor.
An ERISA bond if your plan is subject to ERISA bonding rules. Learn more here: What Is An ERISA Bond And How To Buy One? or compare options via ERISA bond providers. For official guidance, see the Department of Labor’s bonding information: EBSA ERISA fidelity bond fact sheet.
Conclusion: a powerful plan—if you’ll stay eligible and stay organized
A Solo 401(k) can be an excellent retirement plan for self-employed owners who want high contribution potential and 401(k)-style flexibility. The tradeoff is that it’s a real retirement plan with real rules—especially around documentation and annual reporting once your plan reaches certain sizes.
If you want help evaluating whether a Solo 401(k) fits your business today (and what happens if you hire later), consider speaking with a specialist from our 401(k) financial advisors network or exploring providers through our retirement plan providers directory.