Your 401(k) is likely the engine of your retirement plan. For many Americans, it is the single largest asset they own outside of their home. But unlike a pension plan managed by professionals, the responsibility for managing a 401(k) falls squarely on your shoulders.
The difference between a “comfortable” retirement and a “wealthy” one often isn’t about picking the next hot stock—it’s about avoiding unforced errors. Compound interest is a powerful force, but it cuts both ways. While your contributions compound over time, so do fees, penalties, and tax missteps.
Recent data from Vanguard’s How America Saves 2024 report shows that while average account balances are growing, many participants are still leaving money on the table or exposing themselves to unnecessary risks. Whether you are 35 or 65, fixing these common mistakes today could add hundreds of thousands—or even millions—to your final nest egg.
The Essentials: Quick Summary
- Don’t Miss the Match: Leaving the employer match unclaimed costs the average employee over $1,300 per year in free money.
- Watch the Fees: A 1% fee difference sounds small, but over 30 years, it can erode your portfolio value by nearly 20%.
- Know the New Limits: For 2025 and 2026, contribution limits have increased. If you are aged 60–63, you now have access to a massive “super catch-up” contribution.
- Avoid the Tax Bomb: High earners facing the new “Roth Catch-Up” rule in 2026 and retirees managing RMDs need to plan carefully to avoid unexpected tax hits.

1. Leaving “Free Money” on the Table
The employer match is the closest thing to a guaranteed 100% return you will ever find in investing. Yet, remarkably, about 25% of employees do not contribute enough to get the full match. According to research, the average employee who misses out leaves roughly $1,336 per year unclaimed.
That might not sound like “millions” today, but let’s do the math. If you invest that $1,336 annually for 30 years at a 7% return, it grows to over $125,000. And that’s just the match itself—not counting your own contribution that triggered it.
Action Step: Check your plan’s summary description immediately. If your employer matches 50% of the first 6% you contribute, ensure you are contributing at least 6%. Anything less is a voluntary pay cut.