401(k) Retirement Planning Mistakes to Avoid in 2026
401(k) mistakes aren’t just about saving too little – they’re also about poor planning. Common issues like tax-heavy accounts, lack of diversification, and early withdrawals can reduce your retirement income even if your balance is growing.
Takeaways
- Saving money isn’t enough—you need a retirement strategy.
- Too much in pre-tax accounts can create future tax problems.
- Most investors overlook Roth and tax diversification.
- Early withdrawals can reduce long-term retirement income.
- Healthcare costs are often underestimated in retirement planning.
Why Retirement Planning Is So Important
Average retirement account balances rose more than 10% in 2025, according to reports from both Fidelity and Vanguard. [1]
More people are saving.
But having a bigger balance does not automatically mean you are on track for retirement.
In fact, financial advisors are seeing the same costly mistakes show up – even in households with healthy savings. [1]
The mistakes that hurt the most are not about saving too little.
They are about planning too little.
You are not alone if you have been following the “save more” advice but have not thought much about what comes next.
Most people have not.
But the gap between people who retire confidently and those who do not usually comes down to a handful of decisions – not how hard they worked or how much they earned. [2]
Let’s break it down.
Mistake #1: Saving without a Diversification Strategy
What Does “Retirement Rich but Cash Poor” Mean?
Most investors put all their retirement savings into one type of account: A traditional pre-tax 401(k).
That sounds smart, but it creates a problem few people see coming.
It’s often called “retirement rich but cash poor.” [1]
You have money in your 401(k), but almost no flexible cash to tap into when life happens.
Your emergency fund runs dry.
And your only option is to pull from retirement accounts, which comes with taxes and penalties.
If your savings are only in a traditional 401(k), you may have less flexibility than you think, both today and in retirement.
Spreading your savings across different account types could give you more options when you need them.
[Related Read: Traditional 401(k) vs. Roth 401(k): Which Is Right for Me?]
Mistake #2: Ignoring the Tax Bomb Hidden in Your 401(k)
What Are Required Minimum Distributions and Why Should I Care?
A traditional 401(k) grows tax-deferred, meaning you do not pay taxes on the money until you take it out.
That can be a great deal while you are working.
But in retirement, the IRS comes to collect.
Once you turn 73, the IRS requires you to take out a minimum amount from your traditional 401(k) each year.
These are called Required Minimum Distributions (RMDs), and you have to withdraw money whether you need it or not.
These forced withdrawals are taxed as ordinary income.
A large pre-tax balance could push you into a higher tax bracket.
It could also trigger higher Medicare premiums and cause more of your Social Security benefits to be taxed. [1]
To recap: A big balance feels like a win. But without a tax plan, it could cost you more than you expect.
Mistake #3: Skipping Roth 401(k) Planning Entirely
Are Roth Conversions One of the Most Overlooked 401(k) Moves?
Many 401(k) investors save in traditional pre-tax accounts, and very few think about what happens when they start withdrawing. [2]
That is where a Roth 401(k) strategy comes in.
A Roth conversion means moving money from a traditional pre-tax account to a Roth account.
You pay taxes on it now, but from that point on, the money grows tax-free, and qualified withdrawals in retirement are tax-free.
According to Fidelity’s 2026 State of Retirement Planning report, 65-75% of people overlook this move entirely. [2]
That may be a costly oversight.
Think of it this way: Would you rather pay taxes on the seed or the harvest?
A Roth 401(k) lets you pay on the seed.
Tax planning is one of the most powerful parts of retirement planning. And it is also one of the most ignored.
Mistake #4: Cashing Out or Taking Early Withdrawals
How Does 401(k) “Leakage” Quietly Derail Retirement?
Life gets hard sometimes.
A job loss. A medical bill. A family emergency.
It is tempting to tap your 401(k).
You worked hard for that money, so why not use it?
Here is the problem. When you cash out a 401(k) before age 59½, you typically face a 10% early withdrawal penalty plus ordinary income taxes on the entire amount.
Withdraw $20,000, and you might walk away with $13,000 or less after taxes and penalties.
But the hidden cost is even bigger: Lost growth compounding over time.
That $20,000, left alone for 20 years at a 7% average annual return, could have grown to over $77,000.
The industry calls this 401(k) leakage.
Even as average 401(k) balances rose 11% in 2025, hardship withdrawals were still trending upward – a sign that more Americans are raiding their retirement savings during tough times. [3]
The good news is, there are usually alternatives should you need the money.
An emergency fund, a short-term personal loan, or a 401(k) loan (when used carefully) may be better options than a full cash-out.
[Related Read: The Real Impact of 401(k) Hardship Withdrawals]
Mistake #5: Underestimating Healthcare Costs in Retirement
How Much Will Healthcare Really Cost Me in Retirement?
Most people plan for housing, food, and travel in retirement.
Very few plan properly for healthcare.
Out-of-pocket medical costs in retirement could run into the hundreds of thousands of dollars. [2]
Medicare covers a lot, but not everything.
Dental, vision, hearing, and long-term care are largely on you.
One of the most underused tools to prepare for this is a Health Savings Account (HSA).
An HSA offers a triple tax advantage – contributions go in pre-tax and grow tax-free, and qualified withdrawals for medical expenses are also tax-free.
Yet, only about 25% of eligible people contribute to an HSA. [2]
That means 3 out of 4 people are leaving this retirement healthcare tool on the table.
If you have a high-deductible health plan at work, you may be eligible to open an HSA. It is worth checking.
Mistake #6: Chasing a Magic Number without a Spending Plan
Is Saving 10 Times My Salary Enough to Retire?
You have probably heard the rules of thumb: Save 10 times your salary. Follow the 4% rule. Hit $1 million, and you are set.
Those are only rough guidelines, and they may not account for what you need in real life.
Someone earning $125,000 a year may only need around $100,000 per year in retirement.
Why?
Once you stop working, payroll taxes and 401(k) contributions are no longer deducted.
Your actual take-home needs go down even though your lifestyle stays the same. [1]
The bigger risk is the opposite: Obsessing over a number so much that you radically underspend in your working years – sacrificing family experiences, vacations, and quality of life – only to realize you had more than enough all along.
A real spending plan is one that looks at your actual projected expenses in retirement and may serve you far better than any rule of thumb.
Mistake #7: Retirement Planning without Help
Why Is Retirement Planning Different from Saving for Retirement?
Saving for retirement is something most people learn to do on autopilot.
Set a contribution rate. Pick some funds. Done.
But retirement planning is a different discipline entirely.
It involves tax optimization, Social Security timing, Medicare decisions, withdrawal sequencing, and estate planning all at once, and all interacting with each other.
There is often no room for do-overs.
Vanguard’s Advisor’s Alpha research estimates that working with a qualified advisor could add meaningful net value for retirees – primarily through better tax decisions and behavioral coaching during market downturns. [2]
If you find retirement planning complicated, you aren’t alone.
Retirement can be confusing. The rules keep changing. And the stakes can be high.
Getting a second opinion on your plan is not a sign of weakness – it may be one of the smartest financial moves you could make.
At 401(k) Maneuver, we help 401(k) investors like you grow and protect your 401(k) account.
Our professional account management services are designed to:
- Increase long-term performance
- Reduce downside risk
- Help you avoid unnecessary fees
- Keep your investments aligned with your goals
No meetings. No moving your account. No new accounts to open.
Just better management…done for you.
Have questions or concerns about your 401(k) performance? Book a complimentary 15-minute 401(k) Strategy Session with one of our advisors.
Sources
[1] CNBC. As 401(k) balances swell, financial advisors warn of retirement planning pitfalls. April 4, 2026. https://www.cnbc.com/2026/04/04/401k-balances-retirement-planning-pitfalls.html
[2] MoneyTalksNews. 5 High-Impact Retirement Planning Strategies Most People Never Use. April 2026. https://www.moneytalksnews.com/high-impact-retirement-planning-strategies-most-people-never-use /
[3] CNBC. Retirement balances are up, but more workers took hardship withdrawals. March 4, 2026. https://www.cnbc.com/2026/03/04/retirement-balances-hardship-withdrawals.html
