Can I Contribute to Both a Solo 401(k) and a SEP IRA in the Same Year?

Guides · Updated October 2026

I hear this question from freelancers and consultants more than almost any other retirement question: "I already put money in my SEP IRA this year. Can I open a Solo 401(k) too and contribute more?" The answer is yes, usually. But there is a catch that trips up a lot of people, and understanding it can save you from an excess contribution penalty.

The short answer: yes, but the cap is shared

The IRS does not prohibit you from holding both accounts in the same year. What it does is aggregate your contributions. IRS Publication 560, chapter 2, under "More than one plan," says that when you figure the annual additions limit, you must add your contributions to all defined contribution plans you maintain. A SEP IRA counts as a defined contribution plan for this purpose.

For 2026, that shared ceiling is $72,000 of total contributions, or $80,000 if you are 50 or older and eligible for the $8,000 catch-up. For ages 60 to 63, the SECURE 2.0 enhanced catch-up of $11,250 pushes the combined ceiling to $83,250. You cannot put $72,000 in each account. Every dollar into either account eats into the same bucket.

The Form 5305 trap

Here is the catch I mentioned. Many SEP IRAs are established using the IRS model document, Form 5305, because it is the simplest paperwork. A SEP created under Form 5305 cannot coexist with another qualified plan covering the same employees in the same year. If your SEP was set up that way, you are blocked from also running a Solo 401(k).

The fix is straightforward but not automatic: ask your provider whether your SEP was established under Form 5305 or under a prototype SEP document. Prototype documents permit multiple plans. If you are on Form 5305 and want both, you generally need to amend the SEP to a prototype document before contributing to the Solo 401(k). This is a five minute phone call that people skip, and it is exactly the kind of detail that generates excess contribution notices later.

Scenario 1: you already funded the SEP and just learned about the Solo 401(k)

This is the most common real situation, and the good news is it is fully solvable. Take Maya, a freelance brand designer with $95,000 in Schedule C net profit. In March she contributed $17,660 to her SEP IRA, which is roughly 20 percent of her net after the self employment tax adjustment, so she thought she had maxed out.

In October she learns about the Solo 401(k). She opens one before December 31. Her SEP contribution was entirely an employer contribution. The Solo 401(k) gives her a separate employee deferral of up to $24,500 for 2026 that the SEP could never provide. Her new total:

That is comfortably under the $72,000 cap, and she just added $24,500 of tax advantaged savings she would have left on the table. This is the legitimate, everyday reason people run both in the same year: the SEP got funded first, and the Solo 401(k) adds the employee deferral piece afterward. Going forward, she could consolidate everything into the Solo 401(k) and drop the SEP, or keep both. The math is the same either way.

Scenario 2: two genuinely separate businesses

This is where it gets interesting. If you have two unrelated businesses, each business is its own employer, and each employer gets its own $72,000 annual additions limit. The one limit that follows you personally is the $24,500 employee deferral limit, which applies across all 401(k) plans combined.

Say you run a consulting business that funds a SEP IRA, and you also started an e-commerce business that sponsors a Solo 401(k). A legal combined picture could look like:

That exceeds the single employer $72,000 cap, and it is fine, because the contributions came from two separate employers. The businesses must be genuinely unrelated: no overlapping ownership that triggers controlled group rules. If the same person owns both, the IRS may treat them as a single employer. Get a tax professional to confirm before you assume you have two independent limits.

When running both is pointless

For one business with one income stream, running both plans in the same year is almost always wasted complexity. The Solo 401(k) alone reaches the same $72,000 ceiling, and it gives you the employee deferral, the Roth option, and catch-up contributions that the SEP cannot. Adding a SEP on top changes nothing except your paperwork.

The one exception is timing: a SEP IRA can be opened and funded as late as your extended tax filing deadline, while the Solo 401(k) must be established by December 31 of the tax year. If you missed the Solo 401(k) deadline, a SEP is your last minute deduction vehicle. But that is a timing play, not a both plans play.

What I would actually do

My decision rule is simple. One business and no employees: pick the Solo 401(k) and skip the SEP entirely. Already funded a SEP this year: open the Solo 401(k) before December 31, add the employee deferral, then consolidate next year. Two truly separate businesses: coordinate the plans, keep the $24,500 deferral limit in mind, and document everything. And if you have employees beyond a spouse, the Solo 401(k) is off the table anyway, so the question answers itself.

Frequently asked questions

Related: Solo 401(k) vs SEP IRA for S-Corp Owners: A Real-Numbers Tax Breakdown