Can you have a SEP IRA and a Solo 401(k) at the same time?
Yes, you can have both at the same time. We look to the IRS for answers. Whether it works cleanly depends on whether the plans are sponsored by the same employer, and whether your SEP was adopted using the IRS model SEP form.
The two rules that drive the answer
First, the IRS model SEP form. If your SEP was adopted on the IRS model document, Form 5305 SEP, that model form is only allowed if the employer does not maintain any other qualified retirement plan, other than another SEP. A Solo 401(k) is another qualified retirement plan, so a Form 5305 SEP generally cannot coexist with a Solo 401(k) for the same employer.
Second, the contribution limits. A SEP is treated as a defined contribution plan, and when one employer maintains more than one defined contribution plan, contributions are generally combined when applying the annual additions limit. So even if you could maintain both under the same employer, you do not get to double the maximum. The limits still apply in aggregate.
Scenario with two different businesses
Assume you have two businesses that are truly separate employers and are not treated as a single employer under common control or affiliated service group rules.
Business One is XYZ Consulting Inc, an S corporation. You are the only employee. You sponsor a Solo 401(k) in Business One.
Business Two is Coastal Properties Partners LLC, a partnership. You own 20 percent. Other partners own the remaining 80 percent. You do not control the partnership, and it is not part of the same employer group as Business One. Business Two sponsors a SEP.
Because Business One and Business Two are not the same employer, Business One can have its Solo 401(k), and Business Two can have its SEP, at the same time.
How contributions can look in 2026 in this scenario
In Business One, your S corporation pays you W 2 wages of 200,000. In 2026, you can make employee deferrals into the Solo 401(k) up to 24,500. The combined total of employee and employer contributions for that plan is capped at 72,000 for 2026, not counting any catch up contributions you may be eligible for.
In Business Two, you receive eligible compensation or earnings from the partnership. The SEP contribution is generally limited to the lesser of 25 percent of compensation or the annual cap. For self employed individuals the effective SEP rate is 20 percent of net earnings from self employment because of how the calculation works.
The key point is that because the two businesses are separate employers, the plan limits are applied separately at the employer level rather than combining everything into one employer cap.
Important caution
Two businesses that feel separate can still be treated as one employer for retirement plan purposes if there is common control or an affiliated service group relationship. If they are treated as one employer, then the model SEP document issue can block having a Solo 401(k) alongside a Form 5305 SEP, and the contribution limits may need to be aggregated across plans.
If you share your ownership percentages and entity types for the two businesses, I can write a version of this scenario that matches your real structure and show exactly which limits apply where.
Summary
You can have a SEP IRA and a Solo 401(k) at the same time, but the “yes” depends on how the plans are sponsored and documented. If the SEP was adopted using the IRS model document Form 5305 SEP, that form is generally only allowed when the employer does not maintain another qualified retirement plan. Because a Solo 401(k) is a qualified plan, a Form 5305 SEP typically cannot coexist with a Solo 401(k) for the same employer.
Even when maintaining both plans is permitted, the contribution limits do not automatically double. A SEP is treated as a defined contribution plan, and when one employer maintains more than one defined contribution plan, contributions are generally combined when applying the annual additions limit.
A clean example is when you have two truly separate businesses that are not treated as a single employer under common control or affiliated service group rules. In that case, one business can sponsor a Solo 401(k) while the other sponsors a SEP, and each employer applies the plan limits separately. The most important planning step is confirming whether the two businesses are actually separate employers for retirement plan purposes, because that determination controls both whether the plan combination is allowed and how contribution limits apply.
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