One of the most common questions self-employed individuals and small business owners ask is:
“Can I really max out both a Solo 401(k) and a SEP IRA in the same year?”
Watch: Learn When You Can Max Out Both a Solo 401k and a SEP IRA
The short answer: it depends. While both accounts offer powerful tax advantages, the IRS rules determine whether contributions overlap or can be made separately. Let’s break this down.
Solo 401(k) vs. SEP IRA: Key Differences
Solo 401(k)
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Designed for owner-only businesses (with no full-time W-2 employees).
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Contributions can be made as:
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Employee contributions (up to $23,500 in 2025; $31,000 if age 50+).
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Employer profit-sharing contributions (up to 20–25% of net self-employment income).
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Allows voluntary after-tax contributions to support the Mega Backdoor Roth strategy.
SEP IRA
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Primarily for the self-employed but can also be used by businesses with employees.
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Contributions are employer-only profit sharing contributions.
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Does not allow employee contributions or after-tax contributions.
Bottom line: A Solo 401(k) is more flexible—it combines employee and employer contributions, while the SEP IRA is employer-only.
Why Contribution Limits Overlap
If you own just one self-employed business, the IRS treats employer contributions to your SEP IRA and Solo 401(k) as aggregated. That means:
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You cannot double-dip by making the full employer contribution to both accounts.
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If you already contributed the maximum employer amount to your SEP IRA, you cannot make the same employer contribution to your Solo 401(k).
However, once you open a Solo 401(k), many people transfer their SEP IRA into it and continue only with the Solo 401(k), since it allows all contribution types in one plan.
When Can You Use Both?
There is one situation where you may contribute to both:
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You have a self-employed business with a Solo 401(k) and you also work for a completely separate employer that offers a SEP IRA.
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In this case, you can:
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Contribute employer profit-sharing contributions to your Solo 401(k).
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Maximize employer contributions to your employer’s SEP IRA.
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This works because the IRS does not aggregate employer contributions across unrelated employer.
When Keeping Both Might Make Sense
Most self-employed individuals consolidate into just the Solo 401(k). But there’s one exception:
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Form 5500-EZ Filing Threshold
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If your Solo 401(k) balance exceeds $250,000, you must file Form 5500-EZ with the IRS.
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A SEP IRA does not trigger this filing.
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Some business owners maintain both accounts to offload funds into a SEP IRA to stay under the Solo 401(k) reporting threshold.
Smarter Alternatives to Maximize Contributions
Instead of juggling both accounts for the same business, consider:
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Maxing out your Solo 401(k) (employee, employer, and even after-tax contributions).
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Pairing it with a Roth IRA (if your modified adjusted gross income allows).
Why Understanding the Rules Matters
Failing to understand the aggregation rules can result in over-contributions, which lead to:
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IRS penalties.
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Required withdrawal of excess contributions.
By aligning your strategy with IRS rules, you can maximize retirement savings while avoiding unnecessary tax headaches.
Key Takeaway
While it’s tempting to think you can “double up” and max out both a Solo 401(k) and SEP IRA for your self-employed business, the reality is:
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Employer contributions are aggregated if both plans come from the same business.
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You can use both plans only if the SEP IRA is offered by a completely separate, unrelated employer.
For most solopreneurs, the Solo 401(k) is the ultimate “one-stop shop”—allowing employee, employer, and even after-tax contributions. Paired with a Roth IRA, it often provides more flexibility and higher contribution potential than keeping both plans open.
