What Is a 401(k)? A Complete Beginner’s Guide

A 401(k) is a retirement account you get through your job. Part of each paycheck goes into it automatically, and that money is invested so it can grow for decades. You get a tax break, and many employers add free money on top.

1. What a 401(k) is

A 401(k) is named after the section of the tax law that created it. Your employer sets up the plan and picks a company to run it, and you decide how much of your pay goes in.

Each payday, that money goes into your account before it reaches your bank. This is called a payroll deduction. The share of your pay you choose to put in is your contribution rate, such as 5%.

Inside the account, your money buys investments, usually funds that hold many stocks and bonds at once. Over time, they can grow into money you live on after you stop working.

Here's how it adds up. Sam earns $60,000 and puts in 5%. That's $3,000 a year, or about $115 a paycheck if he's paid every two weeks. His employer matches the first 4% of his pay, which adds $2,400. So $5,400 a year goes to Sam's future, and $2,400 of it is money he didn't have to earn himself.

2. The three choices you make

When you sign up, you're really making three separate choices, and getting one right doesn't fix the others.

How much to put in. This is your contribution rate.
How it's taxed. Many plans offer traditional, Roth or both (see section 3).
What it's invested in. You pick from the plan's list of funds.

That last choice matters as much as the first. Two people can each save $200 a paycheck and end up with very different balances because they own different things.

Many plans now sign you up automatically, which is called auto-enrollment. These plans usually start you at a small share of pay, such as 3%, and often put the money in a target-date fund (explained in section 7). Your plan papers list its default rate and fund. That's a fine start, but log in and check both so you know exactly what you own.

3. How taxes work: traditional vs. Roth

A 401(k) can have two tax styles. They hold the same investments, and the only difference is when you pay income tax.

Traditional 401(k): You skip income tax on the money now. You pay income tax when you take it out in retirement.
Roth 401(k): You pay income tax now. Later, your withdrawals are tax-free, growth included, once you're 59½ and have had Roth money in the plan for five tax years. The IRS calls this part of the plan a designated Roth account.

You still pay Social Security and Medicare tax on your contributions either way.

Here's what that means for your paycheck. Your marginal tax rate is the rate you pay on your last dollars of income. Say you're in the 22% federal bracket and put an extra $1,000 into the traditional side. You skip about $220 of federal income tax, so your take-home pay drops by only about $780. Put $1,000 into the Roth side and your take-home drops by the full $1,000. In return, that money comes out tax-free later.

Neither one wins for everyone. A common rule of thumb: traditional tends to help more if you expect a lower tax rate in retirement. Roth tends to help more if you expect a higher one. Many people split their savings. Our guide to traditional vs. Roth 401(k)s walks through the math.

Your employer's match goes in as traditional (pre-tax) money by default. A newer law lets plans offer a Roth match. If your plan does and you choose it, the match counts as taxable income to you that year.

4. The employer match: don't leave free money behind

An employer match is money your company adds when you save. Look in your plan papers for a sentence like "we match 50 cents per dollar on the first 6% you put in."

The rule of thumb many people follow: put in at least enough to get the full match. It's an instant return you can't get anywhere else.

Here's an example. Keisha earns $80,000. Her plan matches 50 cents per dollar on the first 6% of pay.

If she puts in 6% ($4,800), her employer adds $2,400. Total: $7,200 a year.
If she puts in 3% ($2,400), her employer adds only $1,200.

By saving 3% instead of 6%, Keisha gives up $1,200 a year of free money.

Some plans calculate the match each paycheck. If you hit the yearly limit early, you can miss match money in later months. Some plans fix this with a true-up, a make-up deposit after the year ends. Ask your benefits team if yours does.

5. Vesting: when the match is really yours

Vesting means earning the right to keep your employer's money if you leave. The money you put in is always 100% yours from day one.

Employer money often vests over time. With a graded vesting schedule, you earn a share each year. With cliff vesting, you get nothing until a set date, then all of it. Federal law sets the slowest schedules a plan can use for matching money. Cliff vesting must reach 100% after three years. Graded vesting must start at 20% after two years and add 20% a year until you're fully vested after six.

Here's an example. Rosa's plan uses six-year graded vesting. She leaves after three years with $9,000 of match money in her account. She is 40% vested, so she keeps $3,600 of the match. The other $5,400 goes back to the plan. All of her own contributions stay with her.

Your summary plan description spells out your schedule. That's the plain-language rulebook your plan must give you.

6. 401(k) limits for 2026

The IRS caps how much can go in each year. Here are the 2026 limits:

Who	What you can put in from your pay (2026)
Under 50	$24,500
50 to 59, or 64 and older	$24,500 + $8,000 catch-up = $32,500
60, 61, 62 or 63	$24,500 + $11,250 catch-up = $35,750

A catch-up contribution is the extra amount people 50 and older can add. You count as 50 if you turn 50 by December 31. The larger catch-up for ages 60 to 63 is only available if your plan offers it.

A few rules sit on top of those numbers:

One limit, not two. The $24,500 covers your traditional and Roth money combined.
The limit follows you, not your job. Changed jobs this year? Add up what you put in at both. The total can't pass your limit.
Your employer's match doesn't count against your $24,500. But your money plus your employer's money can't go over $72,000 in 2026, not counting catch-ups.

New in 2026: higher earners' catch-ups must go to Roth

Starting in 2026, if you earned more than $150,000 in Social Security wages from your employer in 2025, any catch-up money must go in as Roth. If your plan has no Roth option, you can't make catch-up contributions at that job.

Here's an example. Denise is 56 and earned $165,000 at her job in 2025. In 2026 she can put her regular $24,500 in traditional, Roth or a mix. Her extra $8,000 catch-up must go in as Roth. So she pays income tax on that $8,000 now.

The IRS usually announces next year's limits in November. Check the IRS limits page before you set your 2027 rate.

7. Picking your investments

Your plan gives you a menu of funds. Here are the words you'll see:

Target-date fund: One fund that holds a mix of stocks and bonds. It gets more cautious as its target year (such as 2060) gets closer. It's a simple one-fund choice, but it can still lose money.
Index fund: A low-cost fund that tracks a whole slice of the market, such as the 500 largest U.S. companies.
Asset allocation: Your mix of stocks, bonds and cash.
Diversification: Spreading money across many investments so one company's trouble can't sink you.

Your timeline should shape your mix. If you need the money in 30 years, a big drop this year matters less. If you need it in three, it matters a lot.

Markets do fall. Say Maya has $20,000 in her 401(k) and the market drops 15%. Her balance falls to about $17,000. If she sells now, she locks in the $3,000 loss. If she holds and keeps saving, her new money buys at lower prices. That's why many people keep contributing through rough years. For more, see our investing basics guide.

8. Fees: small numbers, big results

Every fund charges a yearly fee called an expense ratio. It's a percent of what you have invested. A 0.10% fee costs about $10 a year for each $10,000. A 1.00% fee costs about $100.

That gap grows over time. Say Jordan puts in $5,000 a year for 30 years and his funds earn 7% before fees. With a 0.10% fee, he ends up with about $463,900. With a 1.00% fee, he ends up with about $395,300. That's about $68,600 less, just from fees.

Your plan must send you a yearly fee notice. Plans can also charge small admin fees. Compare funds by cost, what they hold and how risky they are, not just by past returns.

9. Taking money out: withdrawals, loans and the 10% penalty

A 401(k) is built for retirement, so early withdrawals cost extra.

The basic rule: Money from a traditional 401(k) is taxed as income when you take it out. If you take it out before age 59½, you usually owe an extra 10% tax too.

Main exceptions to the 10% tax (you still owe income tax on traditional money):

The age-55 rule: You leave your job in or after the year you turn 55. You can then take money from that job's 401(k) penalty-free.
You become totally and permanently disabled, or you're terminally ill.
Up to $5,000 per child for a birth or adoption.
One emergency withdrawal a year, up to $1,000.
Medical bills above 7.5% of your adjusted gross income.

Here's how the age-55 rule works. Luis leaves his job in March of the year he turns 55. He can take money from that job's 401(k) with no 10% penalty. He still owes income tax on it. If he rolls the money into an IRA first, he loses this break, because the age-55 rule doesn't apply to IRAs.

Hardship withdrawals let you take money out for a serious need, such as avoiding eviction. Not every plan offers them. They're not a free pass: you still owe income tax, and usually the 10% penalty.

401(k) loans let you borrow from yourself and repay through payroll. Not every plan offers them. In most cases, the most you can borrow is half your vested balance, up to $50,000. You usually have five years to pay it back. If you leave your job with a loan unpaid, the plan can treat the rest as a withdrawal. You'd owe tax on it unless you put that amount into an IRA or new plan by your tax-filing deadline, extensions included.

Required withdrawals: At 73, you must start taking money out of a traditional 401(k) each year. These are required minimum distributions (RMDs). If you still work there at 73 and your plan allows it, you can wait until you retire. Roth 401(k) money has no required withdrawals while you're alive.

10. When you change jobs

When you leave a job, you have four choices:

Leave it in your old plan, if the plan allows it.
Move it to your new job's plan.
Roll it into an IRA, an individual retirement account you open yourself.
Cash it out. This usually costs the most. You pay income tax, often plus the 10% penalty.

The safest way to move money is a direct rollover. Your old plan sends the money straight to the new account. Nothing is withheld and nothing is taxed.

If the plan sends the check to you instead, it must hold back 20% for taxes. You then have 60 days to deposit the full amount, including the 20% you never got, or the missing part is taxed. Send Roth money to a Roth account and traditional money to a traditional account. Mixing them up can create a tax bill.

11. If you live in New York

Traditional contributions lower your state tax too. New York starts from your federal income, so traditional 401(k) money also skips New York State income tax now, plus New York City income tax if you live in the city.
A break in retirement. Once you're 59½, New York lets you exclude up to $20,000 a year of pension and annuity income. That covers IRA withdrawals and regular, repeating payments from a 401(k). A one-time lump-sum payout from a 401(k) doesn't count. The IT-201 instructions list what qualifies.
Social Security isn't taxed by New York State.

Common 401(k) mistakes

Saving less than the match. Below the match, you're turning down part of your pay.
Never checking your investments. Auto-enrollment picked something for you. Make sure you know what it is.
Cashing out when you change jobs. Taxes and the penalty can eat a big chunk.
Counting unvested match money. It isn't yours until you're vested.
Going over the limit after a job change. The $24,500 is per person, not per job.
Ignoring fees. A 1% fee looks small but can cost tens of thousands over a career.
Forgetting your beneficiary. The person named on your account form gets the money, even if your will says something else. Update it after a marriage, divorce or new baby.

Frequently asked questions about 401(k)s

Can I have a 401(k) and an IRA at the same time?

Yes. They have separate limits, so you can save in both. Having a 401(k) can limit whether you can deduct traditional IRA contributions. See our guide to traditional vs. Roth IRAs.

What if my employer doesn't offer a match?

A 401(k) still gives you a tax break and automatic saving. Compare its fees and fund choices with an IRA. Our guide on which account to fund first can help you decide.

Can I change how much I put in?

Yes. Most plans let you change your rate any time online. Many offer an automatic yearly increase, such as 1% a year, so your savings grow with your raises.

Should I always put in the maximum?

Not always. First cover your bills, build some emergency savings and get the full match. Many people also pay off high-interest credit cards before saving more. Then raise your rate as you can.

Is there a tax credit for saving?

Yes, if your income is modest. The Saver's Credit cuts your tax bill when you save in a 401(k) or IRA. For 2026, it's open if your adjusted gross income is $40,250 or less (single), $60,375 or less (head of household) or $80,500 or less (married filing jointly).

The bottom line

A 401(k) is one of the easiest ways to build wealth: it's automatic, it cuts your taxes and it often comes with free money. Start by getting the full match, check what your money is invested in and keep fees low. Then raise your rate a little each year, and let time do the heavy lifting.

Official sources and further reading

Convivial Wealth education guide · General education for U.S. readers, not personalized tax, legal or investment advice. Figures are for 2026 and are reviewed each year.

Read our full educational disclaimer.