401(k): What It Is, How It Works & Why It Matters
How a 401(k) Works
When you enroll in a 401(k), a portion of each paycheck is automatically directed into your account before you even see it. That money is invested in a menu of options your employer selects — typically a mix of mutual funds, index funds, and ETFs, and sometimes company stock.
With a traditional 401(k), contributions are pre-tax. Your taxable income drops today, and you pay income tax on withdrawals in retirement. With a Roth 401(k), you contribute after-tax dollars — no upfront deduction, but qualified withdrawals in retirement are completely tax-free.
The key advantage either way: your investments grow tax-deferred. No annual taxes on dividends, capital gains, or interest until you withdraw. That compounding without tax drag is what makes 401(k) accounts so powerful over decades.
2025 Contribution Limits
| Category | 2025 Limit |
|---|---|
| Employee contribution (under 50) | $23,500 |
| Catch-up contribution (age 50+) | $7,500 additional |
| Super catch-up (ages 60–63) | $11,250 additional |
| Total limit (employee + employer) | $70,000 |
Employer Match — Free Money You Must Capture
Most employers offer a matching contribution. A common structure: the company matches 50% of your contributions up to 6% of salary. On a $100,000 salary, that’s $3,000 per year in free money — an instant 50% return on those dollars.
Always contribute at least enough to capture the full match. Not doing so is leaving guaranteed, risk-free returns on the table. After capturing the match, consider whether to max out the 401(k) or fund a Roth IRA or HSA next — the optimal order depends on your asset allocation strategy and tax situation.
Investment Options Inside a 401(k)
Unlike an IRA where you can buy almost anything, a 401(k) limits you to a curated menu. Look for low-cost index funds tracking broad markets — an S&P 500 fund, a total market fund, or a target-date fund. Pay close attention to the expense ratio; even a 0.5% difference compounds into tens of thousands over a career.
If your plan has poor options with high fees, contribute enough to get the full employer match, then redirect additional savings to an IRA with better fund choices.
Withdrawal Rules
The 401(k) is designed for retirement, and the IRS enforces that with penalties:
| Scenario | Tax Treatment |
|---|---|
| Withdrawal before age 59½ | Income tax + 10% early withdrawal penalty |
| Withdrawal after age 59½ | Income tax only (traditional) / Tax-free (Roth) |
| Required Minimum Distributions (RMDs) | Must begin at age 73 for traditional 401(k) |
| Rule of 55 | Penalty-free if you leave your job at 55+ (current employer plan only) |
| Hardship withdrawal | Penalty may be waived, income tax still applies |
401(k) Rollover Options
When you leave a job, you have several choices: leave the money in the old plan, roll it into your new employer’s plan, or roll it into an IRA. A direct rollover to a Traditional IRA (or Roth IRA via Roth conversion) is the most common move because IRAs typically offer a wider range of low-cost investments and more flexibility.
Traditional 401(k) vs. Roth 401(k)
| Feature | Traditional 401(k) | Roth 401(k) |
|---|---|---|
| Contributions | Pre-tax | After-tax |
| Tax benefit timing | Tax break today | Tax-free withdrawals later |
| Best if your tax rate… | Is higher now than in retirement | Is lower now than in retirement |
| RMDs required? | Yes, at age 73 | No (since SECURE 2.0, effective 2024) |
| Income limits | None | None |
Not sure which to pick? If you’re early in your career and in a lower tax bracket, the Roth 401(k) often wins. If you’re a high earner near peak income, the traditional 401(k) deduction is more valuable. Many investors split contributions between both for tax diversification.
Key Takeaways
- A 401(k) is an employer-sponsored plan with high contribution limits ($23,500 in 2025, plus catch-ups).
- Always contribute at least enough to capture your full employer match — it’s a guaranteed return.
- Traditional gives a tax break now; Roth gives tax-free income in retirement.
- Withdrawals before 59½ face a 10% penalty (with limited exceptions).
- When you leave a job, consider rolling old 401(k) funds into an IRA for more investment choices.
Frequently Asked Questions
Can I contribute to a 401(k) and an IRA at the same time?
Yes. You can max out your 401(k) and still contribute to a Roth IRA or Traditional IRA (income limits may restrict the IRA tax deduction). This is a common strategy to maximize tax-advantaged savings.
What happens to my 401(k) if I get fired?
The money is yours. Vested employer contributions stay in your account. You can leave it, roll it to your next employer’s plan, or roll it to an IRA. Just avoid cashing it out — you’d owe taxes plus the 10% penalty.
Is a 401(k) better than investing in a brokerage account?
For retirement savings, generally yes — the tax advantages and potential employer match outweigh the flexibility of a taxable brokerage account. A brokerage account has no contribution limits or withdrawal penalties, so it’s better for money you need before retirement.
How do I choose investments in my 401(k)?
Start with low-cost index funds. A target-date fund matching your expected retirement year is a solid one-fund solution. Review your plan’s expense ratios — lower is better. Your asset allocation should reflect your age, risk tolerance, and other investments.