What Happens When You Miss a 401(k) Deadline? The True Cost of Non-Compliance

Managing a company 401(k) plan is a powerful way to build wealth for yourself and your employees, but it comes with a strict fiduciary burden. While most business owners understand that missing an IRS or Department of Labor (DOL) deadline is less than ideal, few realize just how rapidly the financial penalties can escalate.

At Wilson & Associates CPA, we frequently speak with successful Southern California business owners who view their 401(k) plan strictly through an HR lens. However, a retirement plan is a complex financial vehicle, and treating it as a secondary administrative task can lead to crippling penalties, lost tax deductions, and intense regulatory scrutiny.

If you’ve missed a critical 401(k) deadline—whether it was filing your Form 5500, depositing employee contributions, or failing a compliance test—here is exactly what is at risk and the steps you need to take to protect your business.

The Form 5500 is the annual health report of your retirement plan, and missing its deadline triggers dual penalties from both the IRS and the DOL. Unlike standard tax filing penalties, these fines compound daily and can quickly threaten a company’s cash flow.

As of the latest inflation-adjusted guidance for 2026:

• The IRS Penalty: The IRS assesses a penalty of $250 per day for late Form 5500 filings, up to a maximum of $150,000 per plan year.

• The DOL Penalty: The Department of Labor can simultaneously assess a staggering penalty of up to $2,739 per day, with absolutely no maximum cap.

If an employer realizes six months late that their third-party administrator (TPA) or payroll provider failed to file the return, they could be facing hundreds of thousands of dollars in cumulative fines.

One of the most common 401(k) errors is the late deposit of employee deferrals. The DOL requires employers to deposit employee 401(k) contributions into the plan trust as soon as they can reasonably be segregated from the company’s general assets (often interpreted as a few business days, though small plans have a 7-day safe harbor).

If you miss this deadline—even by a few days—it is legally considered a “prohibited transaction,” meaning you have effectively taken an unauthorized loan from your employees’ retirement funds.

• Funding Lost Earnings: You must calculate and deposit the lost investment earnings those funds would have generated.

• Form 5330 Filing & Excise Taxes: You must file IRS Form 5330 and pay a 15% excise tax on the “amount involved” (the lost earnings).

• Audit Red Flags: Late deferral deposits are a primary trigger for full-scale DOL audits.

Strategic tax planning is a cornerstone of wealth preservation. Many high-net-worth business owners utilize heavy profit-sharing and matching contributions to lower their corporate tax liabilities.

However, to legally deduct these contributions on your corporate tax return, they must be deposited by your tax filing deadline (including extensions). If you fund the 401(k) past this date, you cannot deduct the expense for that tax year. For a profitable business making substantial six-figure plan contributions, losing that deduction can result in an unexpected and massive tax bill.

If compliance failures are severe, ignored, or discovered during an IRS audit rather than self-reported, the IRS has the authority to revoke the tax-advantaged status of your 401(k) plan entirely.

Plan disqualification is the worst-case scenario. It means:

• The plan trust becomes a taxable entity.

• The employer loses all prior tax deductions taken for plan contributions.

• Employees must pay immediate income tax on their vested account balances, severely damaging workplace morale and trust.

If you realize a deadline has slipped through the cracks, do not wait for the IRS or DOL to notice. Regulatory agencies are far more lenient on employers who self-correct than those who are caught during an audit.

Depending on the specific failure, our advisory team at Wilson & Associates CPA can help you navigate official correction programs:

• Delinquent Filer Voluntary Compliance Program (DFVCP): If you missed your Form 5500 deadline, filing through this DOL program can reduce your penalties to a fraction of the daily statutory limits (often capping at $2,000 to $4,000).

• Employee Plans Compliance Resolution System (EPCRS): This IRS program allows employers to correct operational errors (like late employee deferrals or missed compliance testing corrections) and retain their plan’s tax-advantaged status.

Reactive accounting is expensive. In the world of high-net-worth tax planning and ERISA compliance, paying for a proactive advisor pays for itself.

At Wilson & Associates CPA, we do more than crunch numbers. We provide white-glove, strategic advisory services and specialize in mandatory 401(k) Plan Audits for growing companies across San Diego, Los Angeles, and Orange County. We ensure your wealth-building strategies remain compliant, secure, and optimized.

If you are concerned about your current 401(k) compliance status or need an expert to untangle past filing errors, it’s time to act.