Form 5500-EZ Solo 401(k) Filing Threshold: When Self-Employed Plans Cross the $250,000 Asset Trigger

You opened a Solo 401(k) years ago when you went freelance. You've been quietly maxing it out, the balance has grown nicely, and you've never filed a single piece of paperwork with the IRS about it. That's been fine — until now. The moment your account balance ticked past $250,000 on December 31, you triggered an annual filing obligation that most self-employed savers don't know exists. Miss the deadline and the penalty is $250 per day, capped at $150,000 per year, per plan.

The good news: the form itself is short, the rules are clear, and even if you've already missed years of filings, the IRS has a permanent relief program that caps the damage at $1,500 per plan. The bad news: the IRS pulled samples of one-participant plan filers a few years back and found that most sponsors they contacted had failed to file at least one Form 5500-EZ. If your plan has ever been over $250,000, this article is the wake-up call worth reading before the July 31 deadline.

What a One-Participant 401(k) Actually Is

The IRS calls them "one-participant 401(k) plans." Everyone else calls them Solo 401(k)s, Solo-Ks, Uni-Ks, or individual 401(k)s. The labels all describe the same thing: a traditional 401(k) plan that covers only a business owner with no common-law employees, or that owner plus a spouse who works in the business.

These plans are popular because they let self-employed people stack two contribution buckets on the same income:

• Employee elective deferral — up to $24,500 in 2026 (Roth or pre-tax)
• Employer profit-sharing contribution — up to 25% of net self-employment compensation

The combined annual limit lands at $72,000 in 2026, before catch-up contributions. The catch-up rules got more interesting under SECURE 2.0:

• Age 50–59 or 64+: standard catch-up of $8,000, bringing employee contributions to $32,500
• Age 60–63: "super catch-up" of $11,250, bringing employee contributions to $35,750
• High earners ($150,000+ prior-year W-2 wages): catch-up contributions must go to a Roth account starting January 1, 2026 — but pure self-employed sponsors with no W-2 wages are exempt from this Roth requirement

That last carve-out is a quiet win for sole proprietors paying themselves entirely through Schedule C: the mandatory-Roth catch-up rule that applies to everyone else doesn't touch you.

Crucially, the perk that makes Solo 401(k)s so attractive — skipping nondiscrimination testing — only survives as long as you have no eligible common-law employees. Hire a part-timer who clocks past the eligibility threshold and you've converted yourself into a regular small-business 401(k) sponsor with full ERISA testing obligations.

The $250,000 Trip Wire

Here is the rule that catches people: a one-participant 401(k) is exempt from filing Form 5500-EZ as long as the combined assets across all one-participant plans you sponsor stay at or below $250,000 at the end of the plan year.

Three details inside that sentence are easy to miss:

1. It's combined, not per-plan. If you have two Solo 401(k)s — say, one held at a brokerage and another at a self-directed custodian for real estate — and one has $200,000 while the other has $80,000, you are over the threshold and both plans require filings.
2. It's measured on the last day of the plan year. For a calendar-year plan that's December 31. A balance that touched $300,000 in October but dropped to $240,000 by year-end does not trigger the requirement that year.
3. It's a one-way door. Once you cross the threshold, you file every year going forward, even if the balance later drops back below $250,000.

There is one additional trigger that catches people who never reached the threshold: the final plan year. If you terminate the plan and distribute all the assets, you owe a final Form 5500-EZ regardless of asset size. Even a $50,000 plan that you decide to roll into an IRA needs that closing return.

When the Form Is Due

Form 5500-EZ is due by the last day of the seventh month after the plan year ends. For a calendar-year plan covering 2025, that means July 31, 2026.

Need more time? File Form 5558 before the original deadline for an automatic 2½-month extension, which moves the deadline to October 15, 2026. Form 5558 is its own filing — submit it on paper to the IRS service center listed in its instructions, and keep a copy with your plan records.

You can file Form 5500-EZ either on paper with the IRS or electronically through the EFAST2 system using Form 5500-EZ. Most modern recordkeepers default to electronic filing. There is one important exception: if you are using the IRS late-filer penalty relief program, you must file on paper — electronic delinquent filings are not eligible for the reduced penalty.

What's Actually on the Form

Form 5500-EZ is a two-page return. It is not a tax return. No payment is due with it. You're reporting basic facts about the plan to the IRS:

• Identifying information: plan name, plan number, sponsor's EIN, plan administrator
• Plan year: start and end dates
• Plan characteristics: what type of features the plan has (a list of three-letter codes like "2E" for a profit-sharing plan, "2J" for a 401(k) feature)
• Financial information: total plan assets and liabilities at the start and end of the year, contributions received, benefits paid, asset transfers
• First/Final/Amended return checkboxes

The financial section is the part where bookkeeping discipline matters. You need year-end balance figures from your custodian, total contributions made for that plan year (which can include contributions made up to the tax filing deadline of the following year), and any distributions.

If your plan holds anything beyond standard mutual funds and ETFs — for example, real estate, private notes, or alternative assets in a self-directed Solo 401(k) — you need defensible year-end valuations. The form asks for fair market value, and the IRS treats unsupported valuations as a documentation problem if they ever audit.

The "First Return" Trap

When the IRS audited a sample of one-participant plan filers, the single most common error was the "first return" checkbox in Part I, Line A. Plan sponsors who had filed prior years on a different form — for example, Form 5500-SF before they realized they qualified for the simpler EZ — would re-check the "first return" box every time they switched. That is wrong.

The rule: check "first return" exactly once, the first time any Form 5500-series return is filed for the plan. After that, the box stays unchecked forever, regardless of which variant of the form you use.

Conversely, the final return checkbox is the one people forget when they close a plan. Distributing all assets and rolling them to an IRA does not, by itself, satisfy the IRS. You need to file a final Form 5500-EZ that shows zero end-of-year assets and the final-return checkbox marked.

Penalties: $250 a Day Is Not a Theoretical Number

The statutory penalty for late or unfiled Form 5500-EZ is $250 per day, up to $150,000 per plan per year, under IRC § 6652(e). For a plan that's been delinquent for several years, the math gets ugly fast: three missed filings can stack to a theoretical $450,000 in penalties.

Penalty letters are not always immediate, but they do come. A common discovery moment: the sponsor terminates the plan years later, files a final Form 5500-EZ that triggers an IRS check of prior years, and receives a notice for the unfiled returns.

If you've missed filings and have not received a penalty notice yet, you have a way out.

The Penalty Relief Program (Rev. Proc. 2015-32)

Revenue Procedure 2015-32 is a permanent IRS program that lets eligible plan sponsors catch up on delinquent Form 5500-EZ returns at a flat fee of $500 per delinquent return, capped at $1,500 per plan.

The eligibility rules are strict but workable:

• The plan must be a one-participant plan (Solo 401(k) or owner-spouse plan)
• You must not have already received a penalty notice from the IRS for the late return — once a CP 283 notice has been issued, that year is no longer eligible
• The filing must be on paper (electronic filings via EFAST2 are not eligible)
• You must mark Check Box D on Part I of each delinquent Form 5500-EZ
• For older returns where Check Box D didn't exist, write in red ink at the top of each paper return: "Delinquent Return Filed under Rev. Proc. 2015-32, Eligible for Penalty Relief"
• Submit a single payment of $500 per return (up to $1,500 per plan total) with a transmittal letter

Mail everything together to the IRS Ogden Service Center address specified in the current Form 5500-EZ instructions. Keep certified-mail proof. Keep copies. The relief is administrative, not statutory, so the documentation matters.

A few practical observations:

• The cap is per plan, not per filer. If you sponsor two separate one-participant plans (e.g., one for a sole proprietorship and one for an S-corp side venture), each plan gets its own $1,500 cap.
• You file the original, not an amendment. A "delinquent" filing is a first-time filing that's late, not a corrected version of something you filed earlier.
• Don't delay if you discover the problem. Once the IRS sends a penalty notice, the cheap door closes for that year.

Recordkeeping That Pays Off at Filing Time

The Form 5500-EZ data points are straightforward, but reconstructing them after the fact when you've changed brokerages, started using a self-directed custodian, or made employer contributions across two tax years is the part that consumes weekends. The defensible approach is to track the plan as its own set of accounts inside whatever bookkeeping system runs your business — separate from your personal investment ledger.

The minimum data you want preserved every year:

• Beginning-of-year and end-of-year asset balances, broken down by custodian if you have more than one
• Every contribution: date received by custodian, dollar amount, source (employee deferral vs. employer contribution), and the tax year it's allocated to
• Every distribution, rollover, or transfer
• For self-directed plans, year-end valuations and supporting documentation (broker statements, appraisals, third-party valuation reports)
• Plan documents and any restatements or amendments

If you're using plain-text accounting (a single ledger file you can grep), it's straightforward to keep a dedicated Assets:Retirement:Solo401k:* account tree for each custodian and tag every contribution transaction with the relevant tax year. When July rolls around and you need year-end totals, the figures are one query away rather than a scavenger hunt across statements.

Edge Cases Worth Knowing

A few situations that commonly cause confusion:

Roth dollars count. The $250,000 threshold is total plan assets, not just pre-tax assets. A Solo 401(k) with $200,000 of pre-tax money and $60,000 of Roth contributions has $260,000 in plan assets and triggers filing.

A spouse's account in the same plan counts. If you and your spouse both participate in the same Solo 401(k) (the plan is structured as an owner-spouse plan), all assets in that plan count toward the single $250,000 threshold for that plan, but you still file only one Form 5500-EZ.

Multiple plans of the same sponsor combine; plans of different sponsors do not. If you and your spouse each run separate businesses and each business sponsors its own Solo 401(k), the assets do not combine for the threshold (assuming the businesses are not part of a controlled group). Controlled-group rules can pull plans together, so if your spouses' business and yours overlap in ownership, talk to a retirement plan specialist before you assume separate thresholds.

A SEP-IRA or SIMPLE IRA does not count. Form 5500-EZ is for one-participant 401(k)/Keogh-type defined contribution plans and one-participant defined benefit plans. SEP-IRAs and SIMPLE IRAs are individual retirement arrangements and have no Form 5500 filing requirement.

Defined benefit plans use the same form. A self-employed person with a one-participant cash balance or defined benefit plan files Form 5500-EZ on the same schedule and uses the same $250,000 threshold (combined with any one-participant defined contribution plans). The actuarial Schedule SB attaches to the EZ for DB plans.

A Practical Checklist for This Year's Filing

Before July 31:

1. Pull December 31 statements for every account inside every Solo 401(k) you sponsor
2. Confirm the combined balance — even if you're certain you're under $250,000, the calculation should be in writing
3. If you crossed the threshold this year for the first time, locate your plan's adoption agreement and identify the EIN, plan number, and plan year
4. Reconcile contributions: employee deferrals (per pay date or per quarter), employer profit-sharing contributions (per tax year), and any rollovers received
5. If you've had a self-directed plan with non-publicly-traded assets, confirm year-end valuations are documented
6. Decide on paper vs. electronic. If using penalty relief, paper is mandatory
7. File Form 5500-EZ (or Form 5558 for an extension) and keep a stamped copy with your plan records

If you have unfiled prior years:

1. Pull the records together for each delinquent year
2. Print Form 5500-EZ for each year (use the year-specific form for older years)
3. Mark Check Box D for years where it exists; for older years, write the red-ink Rev. Proc. 2015-32 statement at the top
4. Attach a transmittal letter
5. Pay the relief fee — $500 per return, max $1,500 per plan
6. Mail everything together to the IRS by certified mail and keep proof

Keep Your Solo 401(k) Records Audit-Ready Year-Round

Solo 401(k) compliance lives or dies on bookkeeping discipline. Year-end balances, contribution allocations across tax years, and rollover histories are the exact data points the IRS expects on Form 5500-EZ — and the exact data points that get lost when records are scattered across brokerage portals and tax-prep folders. Beancount.io provides plain-text accounting that gives you transparent, version-controlled records for every account in your business and your retirement plans, with no proprietary file formats and no vendor lock-in. Get started for free and turn next July's filing from a scramble into a one-query export. For technical setup, see the docs and the Fava dashboard for visual reporting.