What Are The Filing Requirements For Form 5500-EZ And When Does A Solo 401(k) Trigger An Audit

You must file Form 5500-EZ when your Solo 401(k) plan assets reach $250,000 or more at the end of the plan year, or during the final year of the plan regardless of asset value; the IRS does not have a specific audit trigger tied solely to the 5500-EZ itself, but failure to file, late filing, or discrepancies between your return and plan activity significantly raise your audit risk.

Form 5500-ez filing and the $250,000 threshold

The threshold applies to the fair market value of all plan assets as of the last day of your plan year. That date is typically December 31. You count every investment the Solo 401(k) holds. This includes brokerage accounts, mutual funds, real estate purchased with plan funds, promissory notes from participant loans, and even rollover amounts sitting in cash. The IRS does not round down. The exact year-end value controls. If your plan crosses the threshold mid-year, you do not owe a filing until the following January 31 for the year that just ended. You can extend that deadline to April 15.

There is also a mandatory final-year filing rule that catches many owners off guard. If you terminate your Solo 401(k), you must file Form 5500-EZ for the final plan year. You must do this whether you sell the business, retire, or roll the assets into an IRA. This is a one-time filing that reports the plan’s termination date and the distribution of all assets. The IRS uses this to confirm you paid taxes on any taxable rollovers. It also confirms you did not keep the plan alive while skipping the annual report. Missing the final-year filing triggers a penalty. The IRS sets this penalty at $250 per day. The law caps the total penalty at a maximum set by Congress. The IRS often sends a notice within 12 to 18 months after the missed deadline.

The audit risk for a Solo 401(k) comes from behavior, not from filing the 5500-EZ itself.

What actually triggers an IRS audit for a solo 401(k)

The most common red flag is filing late. The IRS imposes a $250-per-day penalty for a late Form 5500-EZ. The audit trigger is the notice you receive after the penalty. Examiners look at late filers to see whether the lateness signals disorganization or an attempt to hide prohibited transactions. A second trigger is a math error on Schedule I. That is the part of the form that lists plan assets and liabilities. The IRS computer flags the return for a document matching review if your total assets do not equal your beginning amount plus contributions minus distributions. This review can escalate to a full examination if the discrepancy exceeds 10% of the plan’s value.

Prohibited transactions are the fastest way to draw an audit. You create a direct audit trigger if you loan plan money to yourself outside the allowed participant loan rules. You also trigger it by buying real estate from a family member using plan funds. Paying yourself a salary from plan assets does the same. In these cases, the IRS receives a Form 1099-R or 5498 that mismatches your 5500-EZ. A contribution that exceeds your earned income for the year creates a similar problem. For example, you net an amount from your sole proprietorship that you report on Schedule C. But you contribute a larger sum as an employer profit-sharing contribution. The IRS computers compare these figures automatically. An overcontribution is a clear sign of a prohibited transaction. It generates a Form 5330 excise tax and a potential audit.

The common mistake of filing when you don't have to

Many Solo 401(k) owners file the full Form 5500 or 5500-SF instead of the EZ when their plan values are below the threshold. They believe that any filing keeps them safer. This is backwards. Filing the 5500-SF when you are not required to do so creates a permanent record of your plan that the IRS never needed. It forces you to answer detailed questions about plan features. These include whether you have a fidelity bond or whether any participants have a vested account. The 5500-SF also requires electronic filing. Your plan data is then stored in the IRS’s EFAST2 system indefinitely. You now have a filed return that contradicts your actual records if you later make a minor administrative error. The IRS can use that inconsistency to open an examination.

The correct approach is simple. File nothing until your plan crosses the threshold. Then file Form 5500-EZ every year thereafter until you terminate the plan. The EZ form is a single page with a schedule. It does not require an independent audit or a CPA signature. Prematurely filing the 5500-SF also creates confusion when you eventually do cross the threshold. You must switch from the SF to the EZ or vice versa. The IRS asks for a reconciliation of prior-year filings. That reconciliation is exactly the kind of paperwork that triggers a document review. Stick to the EZ, wait for the threshold, and you avoid the paper trail entirely. For a deeper comparison of which plan type suits your savings goals, the question of solo 401(k) vs sep-IRA often comes down to contribution limits. The filing obligations differ sharply. A SEP-IRA with no employees has no annual filing requirement regardless of its value. A Solo 401(k) does once it hits the threshold. Both are self-employed retirement plans. The 5500-EZ is unique to the solo 401(k) structure. Knowing your plan type matters more than filing early.

Frequently asked questions

Can I roll my Solo 401(k) into an IRA to avoid the filing threshold?

Yes, rolling the assets into a traditional IRA before December 31 of the year you would cross the threshold eliminates the filing requirement for that year. This works only if the rollover is complete by the plan year-end. The IRA itself has no filing requirement. The rollover must be reported on Form 1099-R. You must terminate the Solo 401(k) plan to avoid a final-year filing.

What happens if I miss the July 31 deadline for an extension?

Filing an extension on Form 5558 gives you until October 15. Missing that extended deadline triggers the $250-per-day penalty. The IRS applies this penalty retroactive to the original July 31 due date. The IRS rarely abates the penalty unless you have a valid reason like a serious illness or a natural disaster. Set a calendar reminder for July 1 each year.

Does a Solo 401(k) with a leased employee count toward the full-time employee rule?

Yes, a leased employee who works more than 1,000 hours per year counts as a common-law employee for plan purposes. This means you can no longer file Form 5500-EZ. You must use the 5500-SF instead. The threshold still applies, but the filing form changes. You must also pass the annual discrimination tests that the EZ form exempts you from. For a deeper dive into how these rules fit within the broader landscape of self-employed retirement plans, see our companion guide, Self-Employed Retirement Plans: What to Know and How to Handle It.