What Is a 401(k)?

How a 401(k) actually works — the money in, the tax break, the match, the ceilings, and every rule about getting it out again, in the order you meet them.

Payroll moves a slice of your pay into an investment account before it ever reaches your bank, your employer usually drops money in alongside it, and the tax bill waits. That's a 401(k). What decides how much you end up with is the match, the fees and the rules about taking it out again, in roughly that order.

How do you set up a 401(k)?

You can't, and that's the part the question hides: a 401(k) is set up by an employer, and what's open to you is enrolling in the plan your employer already sponsors.

If your employer runs a 401(k), enrolling is a short sequence and HR does most of it.

1. Ask the benefits portal or HR for the enrolment form and the summary plan description. The second document decides everything about your plan, and it's yours to read.
2. Choose a contribution rate. Start at whatever collects the entire match, because 50% on the first 6% of pay is an immediate 50% return on that money and nothing else on offer is.
3. Choose pre-tax or Roth if your plan runs both. You can switch in any pay period, so it isn't a decision to lose a weekend over.
4. Choose your funds, or let the default stand. What the default is depends on your plan, and it's named in the summary plan description.
5. Name a beneficiary. This is the two-minute job people skip, and the form you sign here is the one that decides who gets the account.

Plenty of people are already enrolled without having filled in anything at all. Automatic enrolment lets an employer deduct elective deferrals from your wages "unless the employee makes an election not to contribute or to contribute a different amount", and the IRS is blunt about the other half of that: your employer must give you the option, before any deferrals are withheld from your wages, to have none withheld or to have a different amount withheld. So opting out is a right. In a qualified automatic contribution arrangement the default deferral starts at 3% and climbs to 6% as you keep participating, and it can't be set above 10%, all of which is set out on the IRS page for automatic enrollment.

A default rate that starts at 3% sits below the 6% a common formula matches to, so the automatic version of you is usually leaving employer money behind.

If your employer offers no plan, there's no version of this you can open on your own, and no amount of paperwork changes it. The account actually available to you is an IRA, which has a smaller ceiling and applies two income tests a 401(k) never does; what you may put into one depends on what you earn. And if any of your income is self-employed, a solo 401(k) is the one 401(k) you can open for yourself, because in that plan you're the employer.

Payroll takes it before you see it, which is most of why it works

You pick a percentage of pay, and you pick pre-tax or Roth if your plan offers both. Payroll takes it out every period and it lands in your account, invested in whichever of your plan's funds you chose. You never touch it. That's most of why the arrangement works, and it's also why people forget they're doing it.

Your plan may offer pre-tax, Roth, or both:

• Traditional (pre-tax). The contribution comes out before federal income tax, so your taxable income for the year falls by the same amount. Everything is taxed as ordinary income when you withdraw it.
• Roth. The contribution is taxed now, and qualified withdrawals later, including everything it earned, aren't taxed at all.

Which is better comes down to one comparison: your tax rate today against your tax rate in retirement. Nobody knows the second number. That's why the honest answer is a calculation and not a rule, and why the Roth versus traditional calculator runs it at equal out-of-pocket cost. If you want the argument in words before the arithmetic, the two are compared in plain terms here.

The employer match is the actual point

Most employers add money when you do. A common formula is 50% of what you contribute, up to 6% of your salary, so contributing 6% earns you another 3% of salary for nothing.

Nothing else in personal finance pays a guaranteed, immediate 50% return. So the first rule is simple. Contribute at least enough to collect the whole match.

Contributing less is turning down part of your pay, and I'd say that flatly to anyone who asked.

The match sits outside your own IRS contribution limit, so collecting it costs you no room. It does usually sit under a vesting schedule, which is the plan's rule for when the employer's money stops being the employer's. Your contributions are yours from day one. Theirs may take years. The match calculator works out your plan's formula and what you'd keep of the match if you walked out today.

Four ceilings apply in 2026, and they don't stack the way people assume

The four ceilings fall into two groups. The first three are one limit, the cap on what the IRS lets you defer from pay, read at different ages; the fourth caps what the plan may receive from everyone put together.

Almost nobody reaches the combined figure. Every ceiling, with the code section behind it, is set out on its own page, along with the wage floor that forces some catch-up contributions to be Roth.

A $500 deferral costs about $390 of spendable pay

A pre-tax contribution takes less out of your pocket than it puts in the account, because payroll withholds it ahead of federal income tax. Send $500 to the plan at a 22% marginal rate and roughly $390 of it comes out of spendable pay. The rest is tax the year no longer collects.

One qualification surprises people. Social Security and Medicare are withheld on your full wages regardless, so the saving is smaller than your marginal rate alone suggests. The paycheck calculator prices a specific change at your salary and filing status.

A 1% fee quietly takes about a fifth of the balance

Fees, and more than the annual percentage suggests. Your plan charges fund expenses and administration. Both are usually deducted from the balance instead of billed, so nothing ever shows up as a transaction you could question.

A 1% all-in annual fee removes close to a fifth of a working life's balance, because it's charged every year on a balance it has already been shrinking. The figure in dollars is worth seeing once, and the annual fee disclosure your plan has to send you has the percentage to put in.

Can you choose what your 401(k) is invested in?

You choose, but only from a menu somebody else drew up: the committee that runs your employer's 401(k) picks the fund list, and your choice happens inside it.

The Department of Labor puts it carefully. Employees take on responsibility for their retirement income by contributing part of their salary and, "in many instances", by directing their own investments. That hedge is doing work, because 401(k) plans differ wildly. Some offer a long fund list and a brokerage window on top; some offer a handful of index funds and a target-date series and stop there.

If you never choose, your 401(k) chooses for you. The Department of Labor's rule on qualified default investment alternatives lets a plan put an undirected account into a life-cycle or targeted-retirement-date fund, a balanced fund, or a professionally managed account, and that is a list of what's permitted, not a count of what plans pick. How often the target-date option wins, I don't know. I've found no government tally of it.

Which settles the other thing people ask, namely whether a 401(k) is saving or investing. A 401(k) is a tax wrapper, and what sits inside it is invested: funds that rise and fall with markets, with no guaranteed return anywhere in the arrangement except the 50% you get from an employer match. The account earns nothing by itself. The fund menu earns it, and that menu is also where your fees are decided, so the 1% figure above is a fact about your plan's fund list and not about 401(k)s in general.

The rules for getting it out change three times

Each change is tied to an age, and none of them is negotiable.

• Before 59½ a withdrawal is taxed as income and carries a 10% additional tax, unless a statutory exception applies. Leaving your job in or after the year you turn 55 is the most useful one. The withdrawal calculator shows what one would really leave you.
• From 59½ the penalty disappears. The income tax doesn't.
• From 73 or 75, depending on the year you were born, a required minimum distribution has to come out every year whether you need it or not.

Two ways to reach the money without a withdrawal: a plan loan, which isn't taxed if you repay it, and a hardship distribution, which is taxed and usually carries the 10% penalty as well. People mix these up constantly, and the difference matters.

Retiring doesn't move your 401(k) anywhere

Retiring changes nothing inside the account on its own. The balance stays in the same funds, the tax treatment is unchanged, and nothing leaves the 401(k) until you ask for it or until required minimum distributions start at 73 or 75.

What has changed is access. Past 59½ the 10% additional tax is gone, so every dollar you draw from the traditional side is simply ordinary income in the year you take it. It stacks on your Social Security and whatever else you receive, and the same federal brackets that taxed your salary tax the withdrawal. There's no special retirement rate. Qualified withdrawals from the Roth side aren't taxed at all, which is the whole reason the Roth decision years earlier mattered.

Your plan decides the shape of the payments, and that's where people get caught out. The Department of Labor writes it as a permission, never a duty: a defined contribution plan may pay your benefits in a single lump sum as well as offer other options, including payments over a set period of time or an annuity with monthly lifetime payments. May. Which of those yours actually runs is in the summary plan description and nowhere else, so read it before you set a retirement date around a monthly figure. If the options don't fit the life you're planning, moving the balance to an IRA is the usual way to buy flexibility, and it's the same decision you'd face on leaving a job.

Changing jobs is when 401(k) money actually disappears

Nothing, until you decide. Your own contributions are always yours; unvested employer money is forfeited. Then there are four choices, three of them free of tax: leave it, move it to the new plan, roll it to an IRA, or cash out.

This is the moment most 401(k) money is permanently lost, usually by cashing out, because the exit paperwork makes that the easiest box to tick. The four options are compared here, along with the two traps that turn an IRA rollover into a taxable event.

The same machine runs at schools and for the self-employed

The same architecture appears under other names. A 403(b) at a school, hospital or church shares the limits and adds one extra catch-up for long service. If you work for yourself, a solo 401(k) lets you contribute as both employee and employer, which is the whole reason it beats a SEP IRA at modest income.

The beneficiary form outranks your will

If your employer enrolled you automatically, the 401(k) picked two things on your behalf and neither was picked with you in mind. The rate it started you at is usually below the rate that collects the whole match, and the fund it put you in is whatever the plan set as its default. Both settings are defensible. Neither is a decision you made.

The other piece of paper is the beneficiary form, and it beats your will. Whoever is named on the plan's form gets the account, even where the will says something else, and even where the form is twelve years old and names someone you no longer speak to. Marriage adds a layer on top of that. The Department of Labor says that in most defined contribution plans, if you die before you receive your benefits, they automatically go to your surviving spouse, and that naming anyone else takes your spouse's consent, signed as a waiver and witnessed by a notary or a plan representative. People redo their wills after a divorce and never think about the plan.

People run two of these settings together. Your 401(k) contribution rate and your investment choice are separate things. Raising the rate doesn't change what the money buys, and switching funds doesn't change how much arrives. If the funds are expensive, that's an argument about where money above the match should go, never an argument against the match.

None of that sets your rate. That gets solved backwards from the income you want it to pay, and whether you're behind for your age is a different question on a different page, because the balance you already hold moves the required rate further than your salary does.

Frequently asked questions

What is a 401(k) in simple terms?

A retirement savings account that lives at your employer. Money goes in from your pay before it reaches you, your employer often adds some, and nothing inside is taxed while it grows. In exchange the money is meant to stay there until 59½, and taking it out earlier normally costs a 10% penalty on top of the tax.

How does a 401(k) work?

You choose a percentage of pay. Payroll takes it out each period and puts it in your account, where you pick from the funds your plan offers. If your employer matches, their money arrives alongside yours. Nothing is taxed until you withdraw. With a Roth 401(k) the tax is paid going in, and nothing is taxed coming out.

How much can I put into a 401(k)?

$24,500 of your own money in 2026, rising to $32,500 from age 50 and $35,750 in any year you're 60 to 63. Your employer's contribution sits outside that limit and counts instead toward a combined IRS ceiling of $72,000.

Is a 401(k) worth it?

Up to the employer match, it's the highest-return thing available to most people: a 50% match is an immediate 50% return that no fee or market can offset. Above the match it depends on your plan's costs and your tax position. The account itself does nothing. The match and the tax deferral do the work, and both are measurable.

What happens to my 401(k) if I leave my job?

Nothing automatically, and your own contributions are always yours. Employer money may sit under a vesting schedule, so some of it can be forfeited if you leave early. You then choose between leaving the balance, moving it to a new plan, rolling it to an IRA, or cashing out, and only the last of those is taxed.

When can I take money out of a 401(k)?

Without penalty, from 59½. Before that the 10% additional tax applies unless a statutory exception covers you, and leaving your job at 55 or later is the most useful one. From 73 or 75, depending on your birth year, part of the balance has to come out whether you want it or not.