A 401(k) is an employer-sponsored retirement account, named after Section 401(k) of the Internal Revenue Code, that lets you set aside part of each paycheck, invest it through your plan’s menu of funds, and let it grow until retirement. Understanding what a 401(k) is and how it works comes down to five moving parts: the payroll deduction that funds it, any employer match, the tax treatment you choose, the rules about when you can take money out, and what happens to the account when you leave the job. For most American workers, this account has replaced the traditional pension, which means the investment choices and the market risk now sit with you rather than your employer.
How the Paycheck-to-Account Mechanics Work
When you enroll, you pick a percentage of your gross pay to contribute each pay period. That money leaves your paycheck automatically and lands in your retirement account before you ever see it. You can usually change the percentage at set intervals during the year.
Many employers now use automatic enrollment. You’re signed up at a default rate (often 3%) unless you opt out or pick a different number. Some plans also use automatic escalation, which raises your contribution by a percentage point each year. Under a Qualified Automatic Contribution Arrangement, for example, the default starts at 3% and climbs up to a ceiling of 10%.1Internal Revenue Service. Retirement Topics – Automatic Enrollment You can always override the default and set your own rate.
You choose how to invest your contributions from a menu the plan offers. Most plans include mutual funds, bond funds, and target-date funds that automatically shift toward more conservative investments as you approach retirement. If you’re auto-enrolled and never pick an investment, your money typically lands in a qualified default investment alternative, usually a target-date fund matched to your expected retirement year.
Fees matter more than most people notice. Even a half-percentage-point difference in annual fees compounds into tens of thousands of dollars over a career, and your plan’s annual fee disclosure shows what you’re paying in administrative costs and fund expenses.
Employer Matching and Vesting
Many employers match a portion of what you contribute. This is essentially free money added to your balance. Common formulas include a dollar-for-dollar match on the first 3% of salary, or 50 cents per dollar on contributions up to 6% of pay. Not contributing enough to capture the full match is one of the most expensive mistakes workers make.
There’s a catch. Employer matching dollars usually come with a vesting schedule that controls when you actually own them. Your own contributions are always 100% yours. The employer’s share may not be.
- Cliff vesting: you own nothing until you hit a specific service milestone (up to three years), at which point you become 100% vested all at once.
- Graded vesting: ownership builds incrementally, at least 20% after two years of service and rising each year until you reach 100% after six years.2U.S. Department of Labor. FAQs About Retirement Plans and ERISA
Leave the job before fully vesting and you forfeit the unvested portion of employer contributions. Check your schedule before assuming a job change won’t cost you anything.
One exception: safe harbor plans. Under a traditional safe harbor design, the employer either matches 100% of the first 3% you defer plus 50% of the next 2%, or contributes at least 3% of every eligible employee’s pay regardless of whether the employee contributes. Safe harbor contributions are immediately and fully vested, so you own them from day one.
Traditional vs. Roth: When You Pay the Tax
Every plan that allows employee deferrals lets you choose between two tax structures, and the difference is timing.
With a traditional 401(k), contributions come out of your paycheck before federal income tax. That lowers your taxable income now, and the money grows tax-deferred. You pay income tax later, when you withdraw the funds in retirement. Even though traditional contributions dodge federal income tax withholding, they’re still subject to Social Security and Medicare payroll taxes.3Internal Revenue Service. 401(k) Plan Overview
With a Roth 401(k), you contribute after-tax dollars and get no upfront break. In exchange, qualified withdrawals in retirement, including all the investment growth, come out completely tax-free. To qualify, the withdrawal must occur after you turn 59½ and at least five years after your first Roth contribution to the plan.4Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts
The rough rule: if you expect a higher tax bracket in retirement, Roth saves more long-term; if you expect a lower bracket, traditional does. Many people benefit from having some of each, so they can manage their taxable income year by year once they retire.
Starting in 2024, the SECURE 2.0 Act gave employers the option to deposit matching and nonelective contributions directly into your Roth account instead of the traditional pre-tax side. You can only elect Roth treatment for employer contributions if you’re fully vested in those contributions at the time they’re allocated.5Internal Revenue Service. Notice 2024-2 – Miscellaneous Changes Under the SECURE 2.0 Act of 2022 The Roth employer contribution hits your taxable income in the year it’s made, but qualified withdrawals later are tax-free. Not every plan offers this yet; your employer has to amend the plan first.
How Much You Can Contribute
The IRS raises the contribution ceilings each year for inflation. For 2026:
- Employee elective deferral: $24,500. This is the most you can contribute from your own salary across all 401(k) plans you participate in during the year.6Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
- Catch-up for age 50 and older: an additional $8,000, bringing the personal maximum to $32,500.
- Enhanced catch-up for ages 60 through 63: $11,250 instead of $8,000, for a personal maximum of $35,750. This higher tier is a SECURE 2.0 addition aimed at the final years before typical retirement age.
- Total combined limit (employee plus employer): $72,000 across all sources, including your deferrals and any employer match or profit-sharing contributions. For those eligible for catch-up contributions, the combined ceiling is higher by the applicable catch-up amount.7Internal Revenue Service. Notice 2025-67 – 2026 Amounts Relating to Retirement Plans and IRAs
Go over the elective deferral limit and the extra is called an excess deferral. This happens most often when someone switches jobs mid-year and contributes to two different plans. Pull the excess (plus any earnings on it) out of the plan by the due date of your tax return for that year. Miss the deadline and the IRS taxes the excess twice, once in the year you contributed it and again when you eventually withdraw it.8Internal Revenue Service. Consequences to a Participant Who Makes Excess Annual Salary Deferrals
Getting Money Out
The general rule is simple. Withdraw before age 59½ and you owe a 10% additional tax on top of regular income tax.9Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions That’s steep enough to make early withdrawals a last resort.
Several exceptions eliminate the 10% penalty, though regular income tax still applies to traditional 401(k) distributions:
- Rule of 55: if you leave the job during or after the year you turn 55, you can take penalty-free distributions from that employer’s 401(k). This applies only to the plan of the employer you separated from, not to IRAs.
- Total and permanent disability.
- Substantially equal periodic payments: a series of roughly equal payments based on your life expectancy. Once started, you must continue for at least five years or until you reach 59½, whichever is longer.
- Distributions to a beneficiary after the participant’s death.
On the other end, you can’t leave money in a traditional 401(k) forever. Once you reach the required beginning age, the IRS forces you to start pulling money out each year through required minimum distributions. The current beginning age is 73 for anyone born between 1951 and 1959. For those born in 1960 or later, the age rises to 75, effective January 1, 2033.
Fall short in a given year and the IRS imposes an excise tax equal to 25% of the shortfall, dropping to 10% if you correct it within two years.10Federal Register. Required Minimum Distributions Roth 401(k) accounts are no longer subject to RMDs during the account owner’s lifetime, another SECURE 2.0 change.
Loans and Hardship Withdrawals
Most plans let you borrow from your own balance. The maximum is the lesser of $50,000 or 50% of your vested balance, and you generally have five years to repay with at least quarterly payments. If you use the loan to buy your primary home, the five-year deadline doesn’t apply.11Internal Revenue Service. Retirement Topics – Plan Loans
You pay interest to yourself rather than a bank. The risk is what happens if you can’t repay, especially after leaving the job. A defaulted loan is treated as a deemed distribution: the entire unpaid balance becomes taxable income and may trigger the 10% early withdrawal penalty if you’re under 59½.12Internal Revenue Service. Fixing Common Plan Mistakes – Plan Loan Failures and Deemed Distributions A deemed distribution doesn’t erase the debt either; you still owe the plan.
If your plan allows it, you may also be able to take a hardship withdrawal. Unlike a loan, this is a permanent distribution: it reduces your balance and you can’t put it back. The withdrawal must be for an immediate and heavy financial need, and the amount can’t exceed what you actually need for the expense. Qualifying needs the IRS recognizes include medical expenses for you, your spouse, or a dependent; costs of buying a primary home; tuition and education fees; payments to prevent eviction or foreclosure on your primary residence; funeral or burial expenses; repair of damage to your primary home that would qualify as a casualty loss; and expenses from a federally declared disaster if your home or workplace was in the affected area.13Internal Revenue Service. Retirement Plans FAQs Regarding Hardship Distributions Hardship withdrawals are still subject to regular income tax and, if you’re under 59½, the 10% penalty.
What Happens When You Leave the Job
Your 401(k) doesn’t disappear when you leave, but you do need to decide what to do with it. You generally have four options: leave the money in the former employer’s plan (if the balance is above a plan-specified minimum), roll it into a new employer’s plan, roll it into an IRA, or cash it out and accept the taxes and likely penalty.
How you move the money to another retirement account matters enormously. A direct rollover sends the funds straight from the old plan to the new account, with no taxes withheld.14Internal Revenue Service. Rollovers of Retirement Plan and IRA Distributions This is almost always the right move.
With an indirect rollover, the plan writes the check to you instead. It must withhold 20% for federal taxes off the top. You then have 60 days to deposit the full original amount, including making up that 20% from your own pocket, into a new retirement account. Come up short or miss the deadline and the difference counts as a taxable distribution and may also face the 10% early withdrawal penalty. The indirect rollover trips up people who don’t realize they need to front the withheld amount themselves.
You can also roll a traditional 401(k) into a Roth IRA, but the entire converted amount becomes taxable income in the year of the conversion. If you never made after-tax contributions, every dollar you convert is taxable. This strategy works best in years when your income is unusually low, such as a gap between jobs, so the conversion is taxed at a lower rate. There’s no limit on how much you can convert and no penalty regardless of age, but the tax bill can be large if the timing isn’t right.
Newer Features Worth Knowing
The SECURE 2.0 Act, passed in late 2022, added several features that are still rolling out. Two are especially practical for everyday participants.
Employers can now attach a pension-linked emergency savings account to their 401(k) plan. You contribute after-tax (Roth) dollars up to a maximum balance of $2,500, and you can withdraw from the account at least once a month with no need to prove an emergency. The first four withdrawals per plan year are fee-free.15U.S. Department of Labor. FAQs – Pension-Linked Emergency Savings Accounts These contributions count toward your annual elective deferral limit, so they reduce how much you can put into the main 401(k) that year. The point is to give workers a liquid safety net so they don’t raid retirement savings when an unexpected bill hits.
If you’re making student loan payments instead of 401(k) contributions, your employer can now treat those loan payments as if they were deferrals for matching purposes. The match rate must be the same as what the employer provides for regular contributions, and you need to certify your loan payments annually.16Internal Revenue Service. Notice 2024-63 – Guidance Under Section 110 of the SECURE 2.0 Act The provision applies to plan years beginning after December 31, 2023, though not all employers have adopted it yet.