Federal regulators have spent the past year tightening the rules around 401(k) plans, and workers who fail to keep up risk losing tens of thousands of dollars in retirement savings to penalties, taxes, and forgone investment growth. From missed contribution limits and overlooked catch-up rules to early cashouts, hidden fees, and missed tax credits, eight deadly 401(k) mistakes continue to drain American nest eggs, according to guidance published by the IRS, the Department of Labor, and the Government Accountability Office. With new SECURE 2.0 provisions taking effect and updated correction programs rolling out, the cost of ignorance is climbing.
Failing to Hit the Contribution Ceiling
The single most expensive mistake a worker can make is leaving free money on the table. The IRS sets inflation-adjusted caps on elective deferrals each year through its COLA adjustment tables, and workers who do not track those limits often contribute far less than they are allowed. Employees who default to a flat dollar amount when they first enroll and never revisit it can fall thousands of dollars behind over a career, especially when employer matching formulas reward higher deferral rates.
The damage compounds over decades. A worker who contributes even a few thousand dollars less per year forfeits not just the immediate tax benefit but also years of tax-deferred growth on that money. Because the IRS adjusts limits annually for inflation, anyone relying on a contribution rate set five or ten years ago is almost certainly underinvesting relative to what the law permits.
Ignoring the SECURE 2.0 Catch-Up Rules
Workers aged 50 and older have long been eligible for catch-up contributions, but SECURE 2.0 introduced a wrinkle that many savers have not yet absorbed. The law includes a higher catch-up contribution allowance for participants ages 60 to 63, creating a short window of supercharged saving that disappears once a worker turns 64. Missing that window means permanently losing the chance to shelter additional income during peak earning years.
The same legislation also requires that certain higher-earning participants make their catch-up contributions on a Roth (after-tax) basis rather than a pre-tax basis. The Treasury and IRS issued final regulations covering this Roth catch-up mandate and shifted effective dates to give employers more time to update payroll systems. Workers who assume the old rules still apply risk making excess pre-tax deferrals that trigger penalty taxes, or they may stop contributing altogether out of confusion, which is an even costlier outcome.
Cashing Out When Changing Jobs
Job changers who take their 401(k) balance as a lump-sum check instead of rolling it into another qualified plan face an immediate hit from income taxes and, if they are under 59 and a half, a 10 percent early withdrawal penalty. A GAO analysis of leakage in 401(k) plans identified cashouts as one of the primary channels through which retirement savings permanently exit the system. That report, published as GAO-09-715, documented how the combined drag of taxes, penalties, and lost compound growth can reduce a worker’s eventual retirement balance by a significant share.
The problem is behavioral as much as financial. Small balances feel inconsequential, and the friction of initiating a rollover discourages action. Yet even a modest balance left to grow for 20 or 30 more years can multiply several times over. The GAO analysis also flagged hardship withdrawals and plan loans as additional leakage channels, each of which carries its own tax consequences and opportunity costs. Workers who treat their 401(k) as a short-term savings account rather than a long-term retirement vehicle are effectively borrowing from their future selves at punishing rates.
Misunderstanding Loan and Hardship Withdrawal Traps
Taking a loan from a 401(k) can seem harmless because the borrower is technically paying interest to themselves. But the real cost is the investment return that money would have earned while it sat in the market. If a worker leaves the employer before the loan is repaid, the outstanding balance is typically treated as a distribution, triggering taxes and potential penalties. The GAO’s leakage study grouped loans alongside cashouts and hardship withdrawals as the three main drains on plan balances, and the compounding effect of removing money during a market upswing can be severe.
Hardship withdrawals carry an additional sting: unlike loans, they cannot be repaid into the plan. The money is gone permanently, and the worker loses not only the withdrawn amount but every dollar it would have generated over the remaining years until retirement. For younger workers with decades of growth ahead, even a withdrawal of a few thousand dollars can translate into a far larger shortfall at age 65. The lesson from federal data is straightforward: every dollar removed from a 401(k) before retirement costs more than its face value.
Late Deposit of Employee Deferrals
This mistake falls squarely on employers, but employees bear the consequences. When a company withholds elective deferrals from paychecks but fails to deposit them into the plan promptly, the delay constitutes a prohibited transaction under federal law. The IRS fix-it guide for untimely deferrals spells out the exposure: excise taxes on the employer and lost earnings that must be restored to participant accounts.
A common misconception makes the problem worse. Many small-business owners believe they have until the 15th business day of the month following the payroll date to remit deferrals, but the IRS clarifies that this deadline is an outer boundary for determining a prohibited transaction, not a safe harbor. The actual standard is that deferrals must be deposited as soon as they can reasonably be segregated from the employer’s general assets. Employers who routinely wait until the last possible day are flirting with penalties, and their employees’ money sits uninvested in the interim. For workers at small firms, checking that contributions appear in their accounts promptly after each pay period is a simple but effective safeguard.
Overlooking Plan Fees That Erode Returns
Fees are the silent killer of 401(k) wealth. The Department of Labor’s Employee Benefits Security Administration published an educational booklet on 401(k) plan fees that breaks down the categories participants should watch: investment management fees, administrative charges, and individual service fees for actions like taking a loan or processing a hardship withdrawal. Even a difference of half a percentage point in annual expense ratios can reduce a final balance by tens of thousands of dollars over a 30-year career.
Federal rules require plans to disclose fee information to participants, but the disclosures often arrive buried in dense documents that few people read carefully. The DOL guidance encourages workers to compare expense ratios across the investment options in their plan and to ask whether lower-cost index funds are available. Participants who never examine their fee disclosures are effectively agreeing to pay whatever the plan charges without negotiation, and the cumulative drag on returns can rival the damage caused by under-contributing in the first place.
Small-Business Owners Missing Setup and Contribution Deadlines
Self-employed individuals and small-business owners face a distinct set of traps. IRS Publication 560 lays out the rules for SEP, SIMPLE, and qualified plans, including deadlines for establishing a plan, making contributions, and calculating the maximum deductible amount based on compensation caps. Missing the plan setup deadline by even a day can disqualify an entire year’s worth of contributions, and exceeding the compensation cap triggers excess contribution penalties.
The mechanics of elective deferrals for owner-employees also differ from those for rank-and-file workers at large companies. Publication 560 explains how to calculate the maximum deferral when net self-employment income is the compensation base, and errors in that calculation are common. An owner who over-contributes must correct the excess or face a 10 percent excise tax on the amount that should not have gone in. These rules are technical, but the financial stakes for a business owner whose retirement plan is also a key tax-planning tool are high enough to justify professional guidance or, at minimum, a careful reading of the IRS publication each year.
Not Using the DOL’s Correction Programs
When mistakes happen, the federal government offers a path back. The Department of Labor’s Voluntary Fiduciary Correction Program allows plan sponsors to fix fiduciary breaches, including delinquent participant contributions and late loan repayments, without facing the full force of enforcement action. The program includes a Self-Correction Component for cases where lost earnings total $1,000 or less, which lets employers fix small deposit delays without filing a full VFCP application.
The DOL announced improvements to the VFCP that expand the list of eligible transactions, simplify correction procedures, and amend the related class exemption. Those changes carry an effective date of March 17, 2025. Employers who are aware of past deposit mistakes but have avoided correcting them out of fear of the process now have fewer excuses. The updated program lowers the administrative burden of coming into compliance, but it only helps those who actually use it. Plan sponsors who ignore the program and hope regulators never notice are gambling with their employees’ retirement security and their own fiduciary liability.
Skipping Tax Credits Designed for Savers
The IRS offers a Retirement Savings Contributions Credit that directly reduces the tax bill for eligible low- and moderate-income workers who contribute to a 401(k) or similar plan. Despite its value, the credit is widely underused because many qualifying workers either do not know it exists or assume they earn too much to claim it. The credit functions as a direct reward for saving, on top of the tax deferral that 401(k) contributions already provide.
Workers and tax professionals who overlook this credit are leaving a government subsidy unclaimed. For someone already contributing to a plan, the credit requires no additional action beyond checking eligibility and filing the correct form. Combined with the other seven mistakes outlined above, missing the saver’s credit rounds out a pattern of passive losses that, taken together, can hollow out a retirement account long before a worker reaches age 65. The common thread across all eight errors is inaction: failing to check limits, failing to read disclosures, failing to roll over balances, and failing to claim benefits that already exist. Each one is fixable, but only for those who act before the compounding math turns a small oversight into a permanent shortfall.
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*This article was researched with the help of AI, with human editors creating the final content.
Nathaniel Cross focuses on retirement planning, employer benefits, and long-term income security. His writing covers pensions, social programs, investment vehicles, and strategies designed to protect financial independence later in life. At The Daily Overview, Nathaniel provides practical insight to help readers plan with confidence and foresight.
