A 401(k) is a retirement savings account offered through your employer that lets you set aside a portion of each paycheck before (or after) taxes are taken out. The money grows tax-advantaged over time, and many employers sweeten the deal by matching some of your contributions. It’s the most common way Americans build wealth for retirement, and understanding how it works puts you in a much stronger position to use it well.
How a 401(k) Works
When you enroll in a 401(k), you choose a percentage of your paycheck to contribute. That money is automatically deducted each pay period and deposited into your account, where you invest it in a menu of options your employer’s plan provides, typically a mix of mutual funds, target-date funds, and sometimes company stock. Your investments grow without being taxed each year, which lets compounding work more efficiently than it would in a regular brokerage account.
You decide how much to contribute (up to IRS limits) and how to invest. Your employer handles the payroll deduction and works with a plan administrator, usually a financial firm like Fidelity, Vanguard, or Schwab, that holds the accounts and provides the investment options.
Traditional vs. Roth 401(k)
Most plans now offer two flavors, and the difference comes down to when you pay taxes.
With a traditional 401(k), your contributions are deducted from your paycheck before income tax is calculated, which lowers your taxable income right now. You don’t pay taxes on the money or its investment earnings until you withdraw it in retirement. If you earn $80,000 and contribute $10,000, you’re only taxed on $70,000 that year.
With a Roth 401(k), contributions come from after-tax dollars, so you don’t get a tax break today. The payoff comes later: qualified withdrawals in retirement, including all the investment growth, are tax-free. This tends to benefit people who expect to be in a higher tax bracket when they retire, or who simply want the certainty of knowing their withdrawals won’t be taxed.
Many people split their contributions between both types to diversify their tax exposure. Employer matching contributions, regardless of which type you choose, always go into the traditional (pre-tax) side of the account.
Contribution Limits for 2026
The IRS sets annual caps on how much you can put in. For 2026, the employee contribution limit is $24,500, up from $23,500 in 2025. If you’re 50 or older, you can contribute an additional $8,000 in catch-up contributions, bringing your personal limit to $32,500.
Workers aged 60 through 63 get an even higher catch-up limit under a change from the SECURE 2.0 Act: $11,250 instead of $8,000, for a total personal limit of $35,750. This window closes once you turn 64, when you drop back to the standard catch-up amount.
These limits apply only to the money you contribute. Employer matching contributions don’t count against your cap, which means the total going into your account each year can be significantly higher.
Employer Matching Contributions
Many employers match a portion of what you contribute. A common formula is matching 50 cents for every dollar you put in, up to 6% of your salary. So if you earn $60,000 and contribute 6% ($3,600), your employer adds another $1,800. That’s an immediate 50% return on your contribution before any investment gains.
The catch is that employer contributions often come with a vesting schedule, which determines how much of that matching money you actually own based on how long you’ve worked there. Your own contributions are always 100% yours, but employer contributions may vest over time.
There are two common vesting structures. Under cliff vesting, you own 0% of employer contributions until you hit a specific milestone (often three years of service), at which point you’re immediately 100% vested. Under graded vesting, ownership increases gradually, typically 20% per year starting in year two, reaching 100% after six years. If you leave before you’re fully vested, you forfeit the unvested portion of employer contributions. All employees must be fully vested by the time they reach the plan’s normal retirement age, or if the plan is terminated.
Automatic Enrollment Rules
Starting with plans established after December 29, 2022, new 401(k) plans are required to automatically enroll eligible employees. You’ll be defaulted into contributing between 3% and 10% of your pay, and that rate automatically increases by one percentage point each year until it reaches at least 10% (with a ceiling of 15%). You can always change your contribution rate or opt out entirely, but the default nudges people toward saving who might otherwise never sign up.
This requirement doesn’t apply to plans that existed before that date, government and church plans, businesses less than three years old, or employers with 10 or fewer employees. If your plan auto-enrolled you and you want out, you can make a permissive withdrawal early on without the usual penalties.
When You Can Withdraw the Money
A 401(k) is designed for retirement, and the IRS enforces that with a 10% early withdrawal penalty on top of any income taxes owed if you take money out before age 59½. On a $10,000 early withdrawal from a traditional 401(k), you’d owe income tax on the full amount plus a $1,000 penalty.
There are several exceptions where the 10% penalty is waived:
- Separation from service at 55 or older: If you leave your job during or after the year you turn 55, you can withdraw from that employer’s plan penalty-free (age 50 for public safety employees).
- Total and permanent disability
- Death: Beneficiaries can withdraw without penalty.
- Substantially equal periodic payments: A series of fixed withdrawals calculated based on your life expectancy.
- Unreimbursed medical expenses exceeding 7.5% of your adjusted gross income.
- Qualified birth or adoption expenses up to $5,000 per child.
- Federally declared disaster distributions up to $22,000.
- Emergency personal expenses up to $1,000 once per calendar year.
- Terminal illness certified by a physician.
- Military reservists called to active duty.
With a traditional 401(k), you’ll owe income tax on every withdrawal regardless of whether a penalty applies. Roth 401(k) withdrawals are tax-free and penalty-free after age 59½, as long as the account has been open for at least five years.
What Happens When You Leave a Job
You have several options when you leave an employer. You can leave the money in your former employer’s plan if the balance is large enough (plans can force out small balances, typically under $5,000). You can roll the balance into your new employer’s 401(k) if the new plan accepts transfers. Or you can roll it into an individual retirement account (IRA), which often gives you access to a wider range of investment options and potentially lower fees.
The key is to do a direct rollover, where the money moves from one retirement account to another without passing through your hands. If the plan cuts you a check instead, your employer is required to withhold 20% for taxes, and you have 60 days to deposit the full amount (including making up that 20% out of pocket) into another retirement account to avoid taxes and penalties on the distribution.
Why It Matters for Building Wealth
The combination of tax-deferred (or tax-free) growth, employer matching, and automatic payroll deductions makes a 401(k) one of the most powerful tools for retirement savings. Someone contributing $500 a month starting at age 30, earning a 7% average annual return, would have roughly $830,000 by age 65. Add an employer match, and that number climbs substantially.
If your employer offers a match, contributing at least enough to capture the full match is one of the highest-return financial moves available to you. Beyond that, maximizing your contributions up to the IRS limit accelerates your savings and reduces your current tax bill if you’re using the traditional option. Even modest, consistent contributions early in your career benefit enormously from decades of compounding growth.