A 401(k) is a retirement savings account your employer sets up, and you decide how much of each paycheck goes into it

You do not open a 401(k) yourself. Your employer opens it for you — or offers you the chance to join one they already have. The account sits at a financial company (Fidelity, Vanguard, Charles Schwab, or another provider), but your employer controls which provider and what investment options you can choose from. You sign up through your company's payroll or benefits department, usually during your first month of employment or during an annual enrollment period.

Once you are enrolled, you tell your employer what percentage of your paycheck to send into the account before taxes are taken out. That money goes straight from your paycheck into the 401(k) — you never see it in your regular bank account. You then choose how to invest that money from a list of funds your employer's plan offers. The money grows (or shrinks) based on how those investments perform. You cannot touch it without penalty until you turn 59½, with a few narrow exceptions.

The main reason employers offer 401(k)s is that they often match part of what you contribute — meaning they add information programs to your account. That match is the single largest reason to use one if your employer offers it.

Key Takeaways

  • Your employer must offer a 401(k) plan for you to have one; you cannot open one on your own, though self-employed people can open a Solo 401(k) or SEP-IRA instead.
  • You enroll through your company's payroll or HR department, usually within your first 30 days or during the annual open enrollment window.
  • You choose what percentage of your paycheck goes in (typically 1 to 50 percent), and that money is deducted before income tax is calculated.
  • Most employers match a portion of your contribution — commonly 50 percent of the first 6 percent you contribute — which is when ready information programs you should not leave on the table.
  • You choose how to invest the money from a menu of mutual funds and other options your employer's plan provides; you cannot pick individual stocks.

When to enroll and what documents you need

Enrollment happens at two points: when you start a new job, and during your company's annual open enrollment period (usually in October or November). When you are hired, your HR or payroll department will give you a benefits packet that includes the 401(k) plan document, a summary of plan features, and an enrollment form or online portal link. Some companies enroll you automatically at a low percentage (often 3 percent) unless you opt out; others require you to sign up yourself.

You will need your Social Security number and bank account information (for direct deposit, if your employer uses it). You do not need to bring any other documents — your employer already has your tax information on file. The enrollment form or portal asks you to choose a contribution percentage and select your investments from the available options. That is the entire process.

If you miss the initial enrollment window, you can usually enroll during the next annual open enrollment period. Some plans allow you to enroll anytime, but that is less common. Ask your HR department when the next enrollment window opens if you did not sign up when you were hired.

How employer matching works and why it matters

An employer match is not automatic — it depends on what your company's plan offers. The most common match is 50 percent of the first 6 percent you contribute, which means if you put in 6 percent of your salary, your employer adds 3 percent. Some companies match dollar-for-dollar up to 3 percent, others match 100 percent of the first 4 percent. A few offer no match at all.

The match is information programs that appears in your account when ready. If your employer offers a match and you do not contribute enough to receive it, you are leaving that money on the table. For example, if your salary is $50,000 and your employer matches 50 percent of the first 6 percent, contributing 6 percent ($3,000 per year) gets you an extra $1,500 from your employer. Contributing only 3 percent means you only get $750 in matching funds.

The match vests over time, meaning you do not own it when ready — you own it gradually. Vesting schedules vary: some plans vest the match when ready, others over three to five years. If you leave the company before the match fully vests, you forfeit the unvested portion. Check your plan document or ask HR what your vesting schedule is.

Contribution limits and how much you can put in

The IRS sets an annual limit on how much you can contribute to a 401(k). For 2024, that limit is $23,500 per year (or $31,000 if you are 50 or older and make a "catch-up" contribution). Your employer cannot let you contribute more than that, and you cannot contribute more than you earn in a year.

Most people contribute between 3 and 10 percent of their salary. If you earn $60,000 per year, 10 percent is $6,000 annually, which is well below the limit. The limit only matters if you earn a very high salary or are trying to save the maximum amount allowed.

You can change your contribution percentage during open enrollment or, in some plans, anytime during the year. If you get a raise, you can increase your percentage. If money is tight, you can lower it or pause contributions temporarily. Your HR department can walk you through the change process.

Investment choices and how to pick them

Your employer's 401(k) plan offers a menu of investment options — typically 10 to 40 mutual funds and sometimes a stable value fund (which behaves like a savings account). You cannot pick individual stocks or bonds; you choose from what the plan provides. Common options include target-date funds (which automatically shift from stocks to bonds as you approach retirement), index funds that track the overall market, and funds focused on specific sectors or bond types.

If you do not know which funds to pick, target-date funds are a reasonable starting point. A target-date fund for someone retiring around 2055 automatically adjusts its mix of stocks and bonds over time, so you do not have to think about it. Many plans also offer a "managed account" service where a professional adjusts your investments for you, though this usually costs a small fee.

You can change your investment choices during open enrollment or, in most plans, anytime during the year. If you realize you picked the wrong fund, you can move your money to a different one without penalty. Your plan provider's website usually has tools to help you understand each fund's performance and strategy.

What happens to your money when you leave your job

When you leave a company, your 401(k) stays in that company's plan unless you move it. You have four main options: leave it where it is, roll it into your new employer's 401(k) (if they offer one and accept rollovers), roll it into an IRA, or cash it out.

Cashing it out is almost always a mistake. If you withdraw the money before age 59½, you owe income tax on the full amount plus a 10 percent penalty. A $50,000 balance could cost you $15,000 or more in taxes and penalties. Rolling it into an IRA or your new employer's plan avoids that penalty and lets the money keep growing tax-free.

A rollover is straightforward: you contact the old plan's provider and ask for a rollover to your new IRA or 401(k). The money moves directly from one account to the other, and you never touch it. This is the cleanest option and takes about two weeks. Ask your new employer's HR department whether they accept rollovers before you leave your old job.

Tax treatment and how it affects your paycheck

Money you contribute to a traditional 401(k) reduces your taxable income for the year. If you earn $60,000 and contribute $6,000, you only pay income tax on $54,000. This lowers your tax bill now, but you will owe income tax on the money when you withdraw it in retirement.

Some employers offer a Roth 401(k) option, where you contribute after-tax dollars (your paycheck is not reduced), but withdrawals in retirement are tax-free. Roth contributions do not lower your current tax bill, but they can be valuable if you expect to be in a higher tax bracket in retirement. Ask your HR department whether your plan offers a Roth option.

Your 401(k) contributions do not reduce your Social Security or Medicare taxes — only your income tax. You still pay the full 6.2 percent for Social Security and 1.45 percent for Medicare on all your earnings.

Frequently Asked Questions

Can I have a 401(k) if I am self-employed?

No, not a traditional 401(k) — those are only through employers. But you can open a Solo 401(k) (for self-employed people with no employees) or a SEP-IRA, which work similarly. A Solo 401(k) lets you contribute up to $69,000 per year (2024 limit), much more than an IRA. Talk to a tax professional or visit the IRS website to see which fits your situation.

What if my employer does not offer a 401(k)?

You can open an IRA (Individual Retirement Account) on your own through a bank, brokerage, or investment company. IRAs have lower contribution limits ($7,000 per year in 2024, or $8,000 if you are 50 or older) and no employer match, but they give you full control over investment choices. Some employers offer a straightforward IRA as an alternative to a 401(k).

Can I withdraw money from my 401(k) before retirement?

You can, but it costs you. Withdrawals before age 59½ trigger a 10 percent penalty plus income tax on the amount withdrawn. Some plans allow loans against your balance (you repay yourself with interest), which avoids the penalty. A few plans allow "hardship withdrawals" for medical bills, home purchase, or education, but these still carry the 10 percent penalty in most cases.

What happens to my 401(k) if the company goes out of business?

Your money is protected. 401(k) accounts are held by a separate financial company (the plan provider), not by your employer. Even if your employer files for bankruptcy, your 401(k) remains yours. The plan may be frozen temporarily while the company sorts out what happens next, but your balance is safe.

Do I have to invest in stocks, or can I keep my money in cash?

Most plans offer a stable value fund or money market fund that behaves like a savings account, earning a small fixed return. You can keep your entire balance there if you want, though the return is usually 4 to 5 percent per year — lower than stocks over long periods. For money you will not need for many years, stocks historically return more, but stable value is an option if you prefer lower risk.