401(k) glossary
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Administration
Form 5500-EZ
Short definition
Form 5500-EZ is the annual return for a one-participant retirement plan, such as a solo 401(k) that covers only an owner and spouse. It is required once plan assets exceed $250,000 at the end of the year, and for the plan’s final year.
What Form 5500-EZ is
A one-participant plan covers only the business owner, or the partners in a partnership, and their spouses. These plans are outside ERISA’s reporting rules, so they file Form 5500-EZ with the IRS and not the full Form 5500. The return is due on the last day of the seventh month after the plan year ends, which is July 31 for a calendar-year plan. Form 5558 extends that by 2½ months.
Why it matters to employers
The $250,000 threshold counts all of the employer’s one-participant plans together. Once you hire an employee who becomes eligible, the plan is no longer a one-participant plan and moves to Form 5500-SF or Form 5500, with ERISA’s requirements. The IRS can charge $250 a day for a late return, up to $150,000, and runs a penalty relief program for late filers.
Example
A consultant’s solo 401(k) holds $180,000 at the end of 2025, so no return is due. At the end of 2026 it holds $270,000. A Form 5500-EZ for 2026 is due by July 31, 2027.
Common mistakes
Never filing after the plan passes $250,000.
Skipping the final-year return when the plan is closed. It is required whatever the balance.
Continuing to file Form 5500-EZ after hiring employees who are eligible for the plan.
Sources
Internal Revenue Service: About Form 5500-EZ (https://www.irs.gov/forms-pubs/about-form-5500-ez), retrieved 2026-11-11 Internal Revenue Service: Instructions for Form 5500-EZ (https://www.irs.gov/pub/irs-pdf/i5500ez.pdf), retrieved 2026-11-11 Internal Revenue Service: One-participant 401(k) plans (https://www.irs.gov/retirement-plans/one-participant-401k-plans), retrieved 2026-11-11
General information, not legal or tax advice.
