What is a 401(k)? If you’ve ever started a job in the United States, you’ve probably been asked about a 401k retirement plan. Understanding what is a 401(k) and how it works is essential because it forms the foundation of retirement savings for millions of Americans.
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What is a 401(k)?
A 401(k) is a tax-advantaged retirement savings plan offered by employers in the United States. The name comes from the section of the US tax code — Section 401(k) — that governs these accounts.
It allows employees to contribute a portion of their salary to the account before or after taxes, depending on the type of 401(k). The money is then invested — typically in mutual funds, index funds, or target-date funds — and grows over time until retirement.
What Is a 401(k) and How Does It Work?
Here is the basic process:
- Your employer sets up a 401(k) plan and you elect to participate
- You choose what percentage of your paycheck to contribute — up to the annual IRS limit
- Contributions are automatically deducted from your paycheck before or after taxes
- You choose how your contributions are invested from the options your plan provides
- The money grows tax-deferred (or tax-free for Roth) until you withdraw it in retirement
For 2026 the IRS contribution limit for 401(k) plans is $23,500 per year for those under 50, and up to $31,000 for those 50 and older under the catch-up contribution rules. You can verify current limits at IRS.gov.
Traditional 401(k) vs Roth 401(k)
| Feature | Traditional 401(k) | Roth 401(k) |
|---|---|---|
| Contributions | Pre-tax (lowers taxable income now) | After-tax (no immediate tax benefit) |
| Growth | Tax-deferred | Tax-free |
| Withdrawals in retirement | Taxed as ordinary income | Tax-free |
| Best for | Higher earners now, lower income expected in retirement | Lower earners now, higher income expected in retirement |
The Power of Employer Matching
One of the most important parts of understanding what is a 401(k) is employer matching. Many employers match employee contributions up to a certain percentage — for example, matching 100% of contributions up to 3% of your salary.
This is essentially free money — a guaranteed 50-100% return on your investment before a single dollar of market growth. Not contributing enough to get the full employer match is one of the most common and costly financial mistakes American workers make.
Example: You earn $50,000 and your employer matches 100% of contributions up to 3% of salary. If you contribute $1,500 (3%), your employer adds another $1,500 — your retirement account receives $3,000 total instead of $1,500.
Frequently Asked Questions
When can I withdraw from my 401(k)?
You can begin penalty-free withdrawals at age 59½. Withdrawing before this age results in a 10% early withdrawal penalty plus income taxes on the amount withdrawn. There are some exceptions for financial hardship.
What happens to my 401(k) if I change jobs?
You have several options: leave it with your former employer, roll it over to your new employer’s plan, roll it over to an IRA, or cash it out (the least recommended option due to taxes and penalties).
How much should I contribute to my 401(k)?
At minimum, contribute enough to get the full employer match — anything less is leaving free money on the table. Beyond that, aim to contribute 10-15% of your income toward retirement savings across all accounts.
Disclaimer
This article is for informational purposes only and does not constitute financial or tax advice. 401(k) rules, contribution limits, and tax implications are subject to change. Always consult a qualified financial advisor or tax professional for guidance specific to your situation.