Roughly 85% of workers who hold a 401(k) can’t accurately answer basic questions about how their own plan works. Not the fees. Not the vesting schedule. Not what happens to the money if they quit next month. That’s not a peripheral group of uninformed savers – that’s most of the workforce actively contributing to plans they don’t fully understand.
The IRS increased the amount individuals can contribute to their 401(k) plans in 2026 to $24,500, up from $23,500 for 2025 – and yet the bigger problem for most people isn’t the ceiling. It’s the floor. The most costly 401(k) mistakes to avoid aren’t exotic financial blunders. They’re quiet, ordinary oversights that compound silently for decades until the damage is irreversible.
Roughly 92 million Americans collectively hold more than $7 trillion in their 401(k) plans. With that much at stake, the gap between what workers think they know about their retirement accounts and what they actually understand is costing people real money – sometimes hundreds of thousands of dollars by the time they retire. Here are the specific errors that do the most damage.
1. Not Capturing the Full Employer Match
One of the most expensive mistakes workers make is failing to contribute enough to receive the full employer match – an oversight that leaves guaranteed money on the table, since employer matches represent a guaranteed return on investment. The critical detail here is that the mistake isn’t failing to max out the account. According to The Motley Fool, the misstep is specifically failing to put in at least enough of your own money to maximize whatever your employer will add.
The average employer match in 2026 sits between 4% and 6% of salary, according to data from Carry. If you earn $70,000 and your employer matches up to 5%, contributing even 4% means walking away from $700 per year in free compensation – money your employer has already budgeted for you that you’re simply declining to collect. Multiplied over a 30-year career, with compound growth factored in, that choice can cost far more than it appears in any single year.
The fix is mechanical: pull up your plan documents this week, find the exact match formula, and set your contribution rate to at least that threshold. If you’re currently below the match threshold, increasing your contribution by even 1% of salary is almost always worth doing immediately.
2. Ignoring Investment Fees – One of the Biggest 401(k) Mistakes to Avoid
Plan fees are invisible in the same way a slow leak is invisible – you never see the damage happening, only the result after years have passed. According to the U.S. Department of Labor, a 1% difference in annual fees and expenses can reduce your account balance at retirement by 28% over 35 years. That’s not a rounding error. On a balance of $500,000, 28% represents $140,000 gone without a single bad investment decision.
Most 401(k) plans offer a mix of funds with dramatically different expense ratios – the annual percentage of assets the fund takes as its fee. An actively managed fund might charge 0.75% to 1.25%, while an index fund tracking the same broad market might charge 0.03% to 0.10%. Those fractions of a percentage point are where the damage accumulates. Workers rarely check these numbers when selecting funds, and many plans bury fee disclosures in documents few people read.
Check your fund lineup in your plan’s online portal. Every fund should list an expense ratio. If you’re holding funds with ratios above 0.5%, compare them to any available index fund alternatives covering similar assets. Switching to lower-cost options within the same plan requires no rollover and no tax consequence – it’s just a reallocation.
3. Taking Early Withdrawals
The IRS early withdrawal penalty remains 10% of the gross distribution amount in 2026 for distributions taken before age 59½. That 10% hits on top of ordinary income tax, meaning every dollar you pull out early is taxed at your marginal rate and then taxed again by the penalty. A $10,000 early withdrawal typically costs between $3,200 and $4,700 in combined taxes and penalties, depending on your tax bracket.
Hardship withdrawal activity hit a record 6% of 401(k) participants in 2025, up from 4.8% in 2024, according to Vanguard’s How America Saves 2026 report. The median amount withdrawn was small – just $1,900, the same Vanguard data shows. Paying $700 to $900 in penalties and taxes to access $1,900 is an extraordinarily expensive form of emergency borrowing.
There are narrow exemptions to the penalty – including qualified medical expenses and certain disability conditions – but they are specific and limited. If you’re considering a hardship withdrawal, price out a personal loan first. For many people, a short-term loan is cheaper than the tax hit from raiding a 401(k) early. If a true financial emergency requires it, the SECURE 2.0 Act also created a provision for a penalty-free $1,000 annual emergency withdrawal – a far smaller blow than a full hardship distribution.
4. Defaulting on a 401(k) Loan
Many workers use 401(k) loans as a lower-cost borrowing option, and in some circumstances they can be. But the risk of default is real and carries a consequence most borrowers don’t fully grasp before signing. In the event of a default, the IRS treats the unpaid loan balance as a premature distribution, making it subject to income tax and, for workers under 59½, the 10% early withdrawal penalty as well, according to SmartAsset.
The default scenario is most common when workers leave their job – voluntarily or not – while a loan balance remains outstanding. Most plans require the full loan to be repaid by the due date of the tax return for the year of separation. Workers who can’t come up with that cash on short notice watch a routine loan transform into an unexpected tax bill.
If you need to borrow, treat a 401(k) loan like a last resort rather than a routine line of credit. Keep the amount as small as the need allows, set an aggressive repayment schedule, and factor in your job stability before borrowing at all. A layoff during the repayment period can turn a manageable loan into a costly tax event.
5. Misunderstanding Your Vesting Schedule
Some of the most commonly misunderstood 401(k) mistakes to avoid involve employer match money workers believe is already theirs. According to the IRS, matching contributions must be 100% vested when a participant completes 3 years of service under a cliff vesting schedule, or vest gradually over no more than 6 years under a graded schedule. Until those milestones are reached, a portion – sometimes all – of your employer’s contributions can be forfeited if you leave.
Vesting schedules determine when employer contributions become fully owned by the employee: cliff vesting means 100% ownership kicks in at once after a set period, while graded vesting means ownership accrues gradually. Employees who leave before reaching full vesting may forfeit significant employer contributions.
A worker who leaves at 2.5 years under a 3-year cliff schedule walks away with zero employer contributions, regardless of how much was matched into the account. Before accepting a new job offer or timing a resignation, pull up your current vesting schedule and calculate exactly how much employer-contributed money you’d be leaving behind. Even a six-month delay in switching jobs can mean the difference between collecting full vesting and starting from scratch.
6. Botching a Rollover When You Leave a Job
Changing jobs is when 401(k) accounts are most vulnerable to expensive mistakes. Workers who choose an indirect rollover – where the plan sends a check to them rather than directly to the new institution – face two immediate problems. The administrator of your old plan withholds a mandatory 20% for taxes when you take an indirect rollover. You then have only 60 days to deposit the full original amount – not the reduced amount you received – into a new retirement account.
That 20% gap is the trap. If you received $16,000 because the plan withheld $4,000 for taxes, you still owe the IRS proof that $20,000 went into the new account. If you can’t cover the $4,000 shortfall out of pocket within 60 days, that amount is treated as an early distribution, taxed as income, and hit with the 10% penalty if you’re under 59½. A direct rollover – where money moves institution-to-institution without passing through your hands – avoids the mandatory withholding and the 60-day deadline entirely, according to a Motley Fool rollover guide published by Nasdaq.
Always request a direct rollover, also called a trustee-to-trustee transfer. Call both the sending and receiving institutions before you separate from your employer and confirm the exact paperwork required. This is one of the rare financial decisions where the right choice also happens to be the simpler one.
Read More: The 401(k) Rules That Changed in 2025 That Most People Still Don’t Know About
7. Forgetting About Old Accounts
Every forgotten 401(k) sitting at an old employer continues accumulating administrative fees while you ignore it. Workers who change jobs frequently – and the average American changes jobs more than a dozen times over a career – can accumulate several such accounts, each quietly bleeding fees while the investment allocations set years ago drift further from their current goals.
Beyond fees, abandoned accounts are practically difficult to manage. Beneficiary designations may be outdated. And locating the plan administrator after decades becomes progressively harder. The cleaner move at every job transition is a direct rollover to your current employer’s plan or to a personal IRA, handled as soon as you separate.
If you suspect you have forgotten accounts, the Department of Labor’s Abandoned Plan Database can help locate them.
8. Missing Required Minimum Distributions
Required minimum distributions – mandatory annual withdrawals the IRS forces from 401(k) accounts – begin at age 73, according to the IRS. Many workers approaching retirement are unaware of this rule, or believe it only applies to traditional IRAs. It applies to most tax-deferred employer-sponsored plans as well.
Missing your required minimum distribution can result in a penalty equal to 25% of the amount you were supposed to withdraw. On a required distribution of $20,000, that’s a $5,000 penalty – for simply not taking money out of your own account on schedule. The penalty was reduced from 50% under the SECURE 2.0 Act, but it remains severe enough to matter.
The required distribution amount is calculated each year based on your account balance and a life expectancy factor from IRS tables. If you’re approaching 73, set a calendar reminder for December each year and confirm your required amount with your plan administrator or a financial advisor well in advance of the deadline.
What You Can Do Starting This Week
The 401(k) mistakes to avoid listed here share a common thread: they are all invisible until they aren’t. The early withdrawal that felt necessary. The vesting schedule nobody explained. The indirect rollover handled in haste during a job transition. None of these feel like disasters in the moment, but each one carries long-term consequences that can’t be undone once the deadline passes or the penalty is assessed.
Start with what you can verify today: confirm your contribution rate meets your employer’s match threshold, look up your plan’s expense ratios, and read your vesting schedule before your next job decision. Checking your expense ratios alone takes about ten minutes in your plan’s online portal. Switching from a 1% fund to a 0.05% index fund covering the same assets won’t change your tax situation or require a rollover – but over 35 years, that difference can equal or exceed a decade of contributions.
If your contribution rate feels impossible to increase all at once, raise it by 1% now and again with every raise. The workers who retire with enough are rarely the ones who made perfect decisions every year. They’re the ones who stopped making the same avoidable ones – and started with the most basic checks first.
Disclaimer: This information is not intended to be a substitute for professional financial advice, investment advice, tax advice, or legal advice, and is provided for informational purposes only. Always seek the guidance of a qualified financial advisor, accountant, or other licensed professional regarding your personal financial situation or investment decisions. Do not make financial, investment, or tax decisions based solely on information presented here. Past performance is not indicative of future results, and all investments carry risk, including the potential loss of principal.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.
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