At a glance
| Feature | Solo 401(k) | SEP IRA | SIMPLE IRA |
|---|---|---|---|
| Who qualifies | Self-employed with no eligible employees other than a spouse | Any self-employed individual or business, with or without employees | Employers with 100 or fewer employees |
| Employee deferral | Yes | No | Yes |
| Contribution ceiling | Highest of the three; reached on lower income than a SEP | Same top-end as a Solo 401(k), reached at a higher income level | Meaningfully lower than the other two, though still several times a standard IRA limit |
| UDFI exemption (leveraged real estate) | Yes | No | No |
| Participant loan | Yes | No | No |
| Checkbook Control | Built in, no custodian in the chain | Custodial IRA + Trust or LLC | Custodial IRA + Trust or LLC |
| Employer with eligible employees | Not available | Available | Available |
Why is the Solo 401(k) usually the strongest fit for those who qualify?
For someone who qualifies, the Solo 401(k) is the most capable of the three plans in almost every dimension. The employee deferral feature lets you reach the same contribution ceiling as a SEP IRA, but on considerably less income, since a SEP's contribution is capped as a percentage of earnings while the Solo 401(k) adds a flat deferral on top. Add the UDFI exemption on leveraged real estate, the participant loan option, and built-in Checkbook Control with no custodian in the chain, and the Solo 401(k) covers more ground than a SEP or SIMPLE for an eligible owner starting from scratch.
Qualifying is the hard part, and the test runs past a simple headcount into common-law employee classification and controlled-group rules that can pull an otherwise-eligible business out of Solo 401(k) eligibility.
"Usually" is doing real work in that first sentence, though. There are two situations where a SEP or SIMPLE may still be the better call even for someone who qualifies for a Solo 401(k).
You already have a SEP or SIMPLE in place and only want to self-direct part of your portfolio. If most of your retirement savings is going to stay in stocks, funds, or a managed account, redoing your whole plan for a Solo 401(k) is more disruption than the situation calls for. Keep the existing plan for the managed portion and set up a self-directed account for the piece you want to control directly. How you do that depends on whether you're contributing as an employer or as an employee of someone else's plan; both cases are covered below.
The exception to the exception is leveraged real estate or syndications. If a primary goal is debt-financed real estate or a similar leveraged investment, the Solo 401(k)'s UDFI exemption carries enough value on its own to justify the full transition, even if you already have a SEP or SIMPLE running. The tax savings on a leveraged holding, year after year, tend to outweigh the friction of restructuring.
When does a SEP or SIMPLE make more sense?
You're an employee, and your employer's plan lets you direct your own contributions. Some SEP and SIMPLE plans allow each participant to choose where their account is held. If that's the case for you, you can direct your ongoing contributions to your own self-directed account instead of the standard brokerage account your employer defaults to. If you'd rather keep contributing to your current SEP or SIMPLE at your existing brokerage and only self-direct a portion, open a Traditional IRA for that self-directed slice and fund it through a rollover or transfer of the funds you want to move.
You're the employer, and you have plan-eligible employees. This is where the Solo 401(k) is no longer an option; its eligibility rule requires no employees other than an owner or a participating spouse. A SEP or SIMPLE remains available specifically because it's built to cover a workforce. You can set up your own account as a self-directed SEP or SIMPLE IRA and make your contributions there, while your employees continue contributing to whatever provider they use today, or choose to go self-directed themselves if they'd like the same option.
What about contribution limits?
At the top end, the SEP IRA and the Solo 401(k) reach the same annual maximum. The difference is how much income it takes to get there: the SEP's contribution is a fixed percentage of earnings, so reaching the ceiling requires a correspondingly higher income, while the Solo 401(k)'s added employee deferral gets you to that same ceiling on considerably less income. The SIMPLE IRA sits well below both. Its contribution limit is lower than a Solo 401(k) or SEP, but still roughly two to three times what a standard IRA allows, and the current IRA limits give you the baseline those multiples work from.
What does each plan cost you in paperwork?
The SEP is the lightest on ongoing administration. Adopting the IRS model agreement generally relieves you from filing annual retirement plan returns, and there's no fixed annual notice cycle to manage. The SIMPLE carries more structure: you owe eligible employees an annual notice before a defined election period each year, covering their deferral opportunity and your contribution formula for that year. Neither IRA-based plan carries the Form 5500-EZ obligation a Solo 401(k) picks up once year-end plan assets exceed $250,000, but the SIMPLE's notice requirements make it the more process-heavy of the two.
Frequently Asked Questions
Can I switch from a SEP or SIMPLE to a Solo 401(k) later, once I no longer have employees?
Yes, though the SIMPLE carries a timing condition. A SEP IRA rolls into a Solo 401(k) whenever you qualify, while a SIMPLE IRA can only move to another SIMPLE during its first two years, measured from your first contribution. Many owner-only businesses start with a SEP or SIMPLE and roll into a Solo 401(k) once self-employment is established on its own.
Do my employees have to self-direct their accounts if I self-direct mine?
No. Self-direction is a choice each account holder makes independently. Your employees can continue contributing to whatever provider they currently use, or elect to go self-directed themselves if the plan allows it.
Which plan has less ongoing paperwork?
The SEP generally does. Adopting the IRS model agreement typically relieves you of annual retirement plan filings, with no recurring notice cycle. The SIMPLE requires an annual notice to eligible employees ahead of a defined election period each year.
If I currently have a SEP or SIMPLE and later qualify for a Solo 401(k), do I have to give up the existing plan entirely?
Not necessarily right away. You can keep the existing plan for the managed portion of your savings and only self-direct part of it, though if leveraged real estate is a primary goal, the Solo 401(k)'s UDFI exemption is usually worth the full transition.
Can a SIMPLE IRA plan still work if my business grows past a few employees?
Yes, up to 100 employees earning at least the plan's compensation threshold in the preceding year. Beyond that, the SIMPLE is no longer available and a different employer plan structure is needed.
What if only part of my savings is in the SEP or SIMPLE and the rest is already self-directed elsewhere?
That's a normal and common setup. Open a Traditional IRA for the portion you want to self-direct and fund it through a rollover or transfer, while the remainder stays in the existing plan.
Next Steps
Not sure which of the three fits? Plan Finder narrows it based on your employment situation, funding sources, and goals.