Solo 401(k) vs. SEP IRA: Which Plan Fits Your Situation?
Both the solo 401(k) and SEP IRA are designed for self-employed individuals and share the same $70,000 annual ceiling for 2025 — but the path to that ceiling looks very different depending on your income. For a full comparison of all self-employed retirement options, see Retirement Plans For The Self-Employed.
The Core Difference: Two Contribution Buckets vs. One
A SEP IRA uses a single employer-only contribution formula tied to a percentage of your net self-employment earnings. Full contribution rules and the Schedule 1 deduction mechanics are covered in detail at SEP IRA for freelancers.
A Solo 401(K) layers two contribution types — an employee deferral up to $23,500 (plus catch-up if 50+) and an employer profit-sharing contribution up to 25% of net compensation — letting you reach the $70,000 cap at a much lower income than a SEP IRA alone would allow.
At $60,000 net Schedule C profit the gap is significant: a SEP IRA yields roughly $11,100, while the solo 401(k) employee deferral alone reaches $23,500 before the employer portion is even added. See how contribution limits scale with income in the full Solo 401(K) Guide and the SEP IRA contribution limits breakdown.
Where the SEP IRA Wins
The SEP IRA's biggest administrative advantage is simplicity — no EIN, no plan adoption agreement, and you can open and fund one up to your tax filing deadline including extensions. Full setup details are on the Retirement Plans For Self-Employed Overview.
If you have eligible W-2 employees, a SEP IRA requires you to contribute the same percentage for each qualifying employee as you contribute for yourself — a meaningful cost to factor in. For how employee presence changes your plan decision, see the SEP IRA contribution limits guide.
Where the Solo 401(k) Wins
The solo 401(k)'s primary edge at moderate income is its employee deferral, which lets you shelter $23,500 before any percentage-based calculation applies — something no IRA-style plan can match. For full details on the Roth option and loan provisions, see the Solo 401(K) Guide.
The solo 401(k) does carry more administrative requirements: you need an EIN, the plan must be established by December 31 of the tax year, and Form 5500-EZ applies once assets exceed $250,000. Full setup requirements are in the Solo 401(K) Guide.
How the SIMPLE IRA Fits In
For solo operators comparing all three plans, the SIMPLE IRA is generally the weakest fit — its 2025 deferral limit of $16,500 is lower than the solo 401(k)'s $23,500 and it carries mandatory employer contribution requirements. Where the SIMPLE IRA fits and how to evaluate it against the others is covered in the Solo 401(K) Guide.
How to Choose
- Net income under $100,000 and you want to maximize contributions: the employee deferral structure of the Solo 401(K) lets you shelter far more than a SEP IRA at this income range.
- You missed December 31 and haven't opened a plan yet: a SEP IRA is the only option you can still fund for the prior tax year — see SEP IRA for freelancers for deadline details.
- You want a Roth option or anticipate needing a plan loan: a SEP IRA offers neither — the Solo 401(K) covers both features in detail.
- You have W-2 employees now or expect to hire soon: consult a CPA — your plan choice affects what you're required to contribute on their behalf.
- High income ($200,000+) and the $70,000 cap feels limiting: the Self-Employed Retirement Plan Comparison covers defined benefit options that can go beyond the defined-contribution ceiling.
This comparison is based on 2025 IRS rules and is an estimate, not a substitute for professional tax advice. For a complete look at all self-employed retirement plan options, see Retirement Plans For The Self-Employed.