What are the most common mistakes with 401(k) plans, and how can you avoid them?

By FastBuySale Newsroom · 5 Nov 2026 · 35m ago

Mistake 1: leaving the employer match on the table

Common mistakes with 401(k) plans usually come down to a handful of avoidable habits: contributing too little to collect the full employer match, not knowing the annual limits, cashing out when changing jobs, and ignoring the rules that apply later in life. Fixing them rarely needs special products, just attention to how your plan works.

The Internal Revenue Service (IRS) announced in November 2025 that the employee contribution limit for 401(k), 403(b), governmental 457 plans and the federal Thrift Savings Plan rises to $24,500 for 2026, up from $23,500 for 2025. Workers aged 50 and over can generally add a catch-up contribution of $8,000, for a total of $32,500, and workers aged 60, 61, 62 and 63 have a higher catch-up limit of $11,250.

Many employers add matching contributions when you defer part of your salary. A common formula matches a percentage of what you put in, up to a cap set by the plan. If you contribute below that cap, you are effectively declining part of your pay package. The exact formula varies by employer, so the first step is to read your plan's summary plan description or ask your HR or benefits team.

A second trap is vesting. Employer contributions may vest over several years under a schedule written into the plan, while your own deferrals are always yours. Leaving a job just before a vesting date can forfeit employer money, so it is worth knowing your plan's schedule before you make career moves.

Practical fix: set your deferral at least to the level that captures the full match, then raise it by a percentage point at each pay rise. Many plans offer an automatic escalation feature that does this for you.

Readers evaluating 401(k) plans should separate marketing claims from the actual rule text that governs their account or product. When two summaries disagree, the governing document or statute wins. If a rule depends on your age, filing status, or income band, re-check it when any of those facts change. Life events quietly move people across thresholds they last reviewed years earlier.

Educational explainers like this one cannot replace personalized advice for complex situations such as divorce orders, inherited accounts, or cross-border tax residency. Escalate those cases to a qualified professional. When in doubt about a number that changes every year, describe your plan qualitatively first, then look up the current official figure for the tax year you care about before you act.

Mistake 2: not knowing the 2026 limits

Contributing too much can be as awkward as contributing too little. For 2026 the IRS limit on elective deferrals is $24,500. If you are 50 or older, the general catch-up limit is $8,000, so most participants in that age group can defer up to $32,500. Under the SECURE 2.0 Act of 2022, employees aged 60, 61, 62 and 63 get a higher catch-up limit, which the IRS says remains $11,250 for 2026 instead of $8,000.

The limit applies per person, not per plan. If you change employers mid-year or work two jobs with 401(k) plans, the deferrals in both count toward the same annual cap. Each payroll department only sees its own plan, so it is up to you to keep the combined total within the limit; excess deferrals generally need to be corrected promptly with the plan to avoid being taxed twice.

Smaller employers sometimes offer SIMPLE plans instead. The IRS set the 2026 SIMPLE contribution limit at $17,000, up from $16,500, with a catch-up of $4,000 for most participants aged 50 and over. Knowing which plan type you are in prevents you from planning around the wrong number. You can model how a higher deferral affects take-home pay with the calculators at

A useful habit is to write down your goal, time horizon, and cash buffer before you change any election related to 401(k) plans. Decisions made during a stressful week are the ones people reverse later at a cost. Educational explainers like this one cannot replace personalized advice for complex situations such as divorce orders, inherited accounts, or cross-border tax residency. Escalate those cases to a qualified professional.

Mistake 3: cashing out or borrowing carelessly

When you leave a job you can usually leave the money in the old plan, roll it into a new employer's plan, roll it into an IRA, or take it as cash. Cashing out is the option that most often hurts. Distributions from a traditional 401(k) are generally taxable income, and the IRS generally applies an additional 10% tax on early distributions taken before age 59 and a half, unless an exception applies.

A direct rollover, where the money moves from one plan or custodian straight to another, avoids that tax hit and keeps the savings invested. If a check is made out to you instead, the IRS says the plan may withhold tax and you have 60 days from the date you receive it to deposit the funds into another eligible plan or IRA to avoid the distribution being treated as taxable.

Plan loans are another area to handle with care. Not every plan offers them, and each plan sets its own terms. Before borrowing, read your plan's loan rules carefully, including what happens to any unpaid balance if your job changes, and compare the cost with other options.

Keep digital and paper copies of confirmations after every change. Screenshots of election pages, email receipts, and year-end statements make tax season and job changes far less chaotic. Compare fees the same way you would compare two similar listings before you buy: look at what you pay each year, what you get, and whether a simpler option meets the same need.

Mistake 4: ignoring investments, fees and beneficiaries

Money deferred into a 401(k) does not grow on its own; it has to be invested in the options your plan offers. Some participants never choose and end up in a default fund, which may or may not suit them. Others pick once and never review. A yearly check of your investment mix, the fees shown on your plan's fee disclosure, and how the mix matches your time horizon is a simple habit that avoids drift.

Beneficiary designations are just as important. The beneficiary form on file with the plan usually decides who inherits the account, so an outdated form after a marriage, divorce or birth can send money somewhere you no longer intend. Update it whenever your circumstances change.

Finally, remember that taxes come due eventually for pre-tax money. Required minimum distributions generally start at age 73 for workplace plans, although participants who are still working and do not own 5% or more of the employer can generally delay RMDs from that employer's plan until they retire. Designated Roth accounts in a 401(k) are not subject to RMDs while the owner is alive. Browse more retirement explainers at and

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If a rule depends on your age, filing status, or income band, re-check it when any of those facts change. Life events quietly move people across thresholds they last reviewed years earlier. Automation helps. Calendar reminders for annual reviews, automatic transfers, and beneficiary checkups reduce the chance that a good plan dies from neglect.

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