401(k) Basics: How It Works
A 401(k) is a retirement account your employer offers that lets you invest part of each paycheck before you ever see it. It is the single most powerful wealth-building tool most Americans have access to — and a surprising number of people leave part of its value on the table.
What a 401(k) actually is
You choose a percentage of your salary to contribute each pay period. That money goes into investments you pick from your plan’s menu (usually mutual funds), and it grows tax-advantaged for decades. Because contributions come straight out of your paycheck, you never face the monthly “should I invest?” decision — it just happens.
The employer match: free money with a catch
Many employers match part of your contribution — the classic formula is 50% of what you put in, up to 6% of your salary. Contribute 6%, get an extra 3% from your boss. Contribute 3%, get 1.5%. It is an instant 50% return before the market does anything. The “catch” is only that you must contribute enough to capture the full match. Not doing so is the most expensive mistake in this entire article.
Employer matches 50% → +$2,400/year free.
Over 30 years at 7% growth, that match alone compounds to roughly $245,000.
2025 contribution limits
- Under 50: up to $23,500 of your own contributions per year.
- 50 and older: an extra $7,500 catch-up, for $31,000 total.
- Employer matches do not count against your limit — they have a separate, much higher combined cap.
Traditional vs Roth 401(k)
- Traditional: contributions reduce your taxable income now; you pay tax when you withdraw in retirement. Usually better if you expect to be in a lower bracket later.
- Roth: you contribute after-tax dollars, but withdrawals in retirement are tax-free. Usually better when you are young and your income (and tax rate) will likely rise.
- Many plans let you split between both. When in doubt, consider your age: young earners often favor Roth.
Vesting: when the match becomes yours
Your own contributions are always 100% yours. Employer matching dollars, though, may follow a vesting schedule — for example, 20% per year over five years. Leave after two years and you might keep only 40% of the match. Check your plan’s schedule before changing jobs.
See what decades of contributions plus the match can do with our 401(k) calculator.
What happens to my 401(k) if I change jobs?
Common options: leave it, roll it into your new employer’s plan, or roll it into an IRA. Cashing it out triggers taxes plus a 10% early-withdrawal penalty if you are under 59½ — usually a terrible deal.
Should I invest beyond the employer match?
Capture the full match first — nothing beats an instant 50–100% return. After that, many people max an IRA (more investment choices) before adding beyond-the-match 401(k) contributions.
Can I withdraw early in an emergency?
Most plans allow hardship withdrawals or loans, but both come with costs: taxes, penalties, and lost compounding. Treat the 401(k) as locked until retirement.