How a 401(k) Works (and What an Employer Match Really Is)

A 401(k) is a retirement savings account you can use through your job. The "401(k)" is just the section of the federal tax code that authorizes it. The real point is that you can put money in straight from your paycheck, get tax benefits, and often get free money from your employer in the form of a match.

This is a plain-English explainer. For a feel for how the money grows over decades, see How Compound Interest Works and the investing basics overview. For more vocabulary, see compound interest and interest rate.

How the money gets in

You sign a form (often online) telling your employer to send a percentage of each paycheck to the 401(k). The money goes in before federal income tax is calculated, so it lowers your taxable income for that year. That is the first tax benefit.

Inside the account, you choose investments — usually a menu of mutual funds curated by the plan. The money grows tax-deferred (no yearly tax bill on dividends or gains).

There is also a Roth 401(k) option in many plans. With Roth, the money goes in after tax, but qualified withdrawals in retirement come out tax-free. The IRS publishes the official rules at IRS Retirement Plans.

The employer match: the closest thing to free money

Many employers offer a match — they put in extra money based on what you contribute. A common structure is:

• "100% match on the first 3% of pay, then 50% match on the next 2%."
• Translation: if you contribute 5% of your salary, your employer adds 4%.

If you make $50,000 and contribute 5% ($2,500), your employer adds $2,000. You did not have to do anything special to earn it — just contribute. Personal finance educators almost universally suggest contributing at least enough to get the full match, because skipping it is the same as turning down a raise.

The U.S. Department of Labor's Employee Benefits Security Administration (EBSA) supervises workplace retirement plans and publishes a free participant guide at dol.gov/ebsa.

What "vesting" means

Your own contributions are always 100% yours. The employer's contributions usually have a vesting schedule — a timeline you have to stay employed before that money is fully yours.

Two common vesting schedules:

• Cliff vesting — you own 0% of the match until a certain date (often 3 years), then 100%.
• Graded vesting — you own 20% after one year, 40% after two, and so on until 100% (often after 5-6 years).

If you leave before you are fully vested, you forfeit the unvested portion. EBSA requires plans to give you a clear vesting schedule in your Summary Plan Description.

Contribution limits

The IRS sets a yearly limit on how much you can contribute. For example, recent years have allowed roughly $23,000 for people under 50, with a higher catch-up amount for people 50 and older. The match does not count against your personal limit. Always check the current number at IRS Retirement Plans.

The investments

Most plans offer a list of mutual funds. Common categories:

• Target-date funds — a single fund that automatically shifts from stocks to bonds as you approach a target retirement year. The plan default for most newer 401(k)s.
• Index funds — funds that try to match a broad market index (like the S&P 500) at very low cost.
• Actively managed funds — funds that pick stocks, usually at higher cost.

The Securities and Exchange Commission's beginner site, Investor.gov, has a plain-language guide to picking funds and a free fee calculator. Even small fee differences compound into real money over 30+ years.

Withdrawals and the early withdrawal penalty

You can usually withdraw money penalty-free starting at age 59½. Pull money before then and the IRS adds a 10% early withdrawal penalty on top of the regular income tax (with limited exceptions: first-time home purchase, certain medical bills, qualified disability, etc.).

Many plans offer a 401(k) loan — borrowing from your own balance. The CFPB and EBSA both warn that 401(k) loans come with real risks, especially if you change jobs, because the loan often has to be paid back fast or it counts as a withdrawal.

When you change jobs

You generally have four choices for the old 401(k):

1. Leave it where it is (if the balance is high enough — many plans require this).
2. Roll it into your new employer's plan.
3. Roll it into an IRA at a brokerage of your choice.
4. Cash it out — usually the worst option, because of taxes and the 10% penalty.

Investor.gov, EBSA, and the CFPB all walk through how rollovers work without triggering taxes.

A note on advice

This is general information, not advice. Talk to a fee-only fiduciary or a qualified tax pro about your situation, especially as your balance grows or when you change jobs. A 401(k) plan committee at work can answer plan-specific questions, and most plan websites offer free, plan-paid education sessions.

Numbers and rules in this article change every year — always check the latest from the IRS, CFPB, and your state's insurance / consumer protection department.