A 401(k) is an employer-sponsored retirement account, and understanding how 401(k) plans work comes down to a simple sequence: money leaves your paycheck before you see it, lands in an investment account in your name, grows with tax advantages for decades, and comes out in retirement under rules that reward patience and penalize early access. Your employer may add to the account on your behalf. You choose how the money is invested from a menu the plan provides. The IRS caps how much can go in each year and dictates when it has to start coming out.
How Your Contributions Move From Paycheck to Account
Each pay period, a percentage of your gross pay that you selected at enrollment is withheld and deposited into your 401(k). You never take possession of that money, which is part of why the plan works: automation removes the monthly decision to save.
The tax treatment depends on which type of contribution you chose. A traditional 401(k) contribution comes out of your paycheck before federal income tax is calculated, which lowers the taxable wages reported on your W-2 and reduces your tax bill for the year.1Internal Revenue Service. 401(k) Resource Guide – Plan Participants – 401(k) Plan Overview Every dollar you eventually withdraw in retirement is then taxed as ordinary income.2Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3
A Roth 401(k) contribution works in reverse. You pay tax on the money now, so your take-home is lower, but qualified withdrawals in retirement come out completely tax-free, including all the investment growth. A withdrawal counts as qualified only if it happens at least five years after your first Roth contribution to the plan and after you reach age 59½ (or become disabled or die).3Internal Revenue Service. Retirement Topics – Designated Roth Account Pull money out before meeting both conditions and the earnings portion is taxable and may face an additional 10% penalty.
Many plans let you split contributions between the two types. The right choice depends on where you think your tax rate is headed. If you expect a lower bracket in retirement, traditional saves more overall. If you think taxes will be higher later, Roth locks in today’s rate.
What Your Employer Adds
Many employers match a portion of what you defer, which is essentially free money added to your account. A common formula is a dollar-for-dollar match on the first 3% to 6% of your salary that you contribute. Others match 50 cents on the dollar. The specifics vary widely.
Only the first $360,000 of your compensation in 2026 can be used when figuring matching contributions. If you earn more, the employer’s formula ignores the excess.
Employer matching dollars almost always go in on a pre-tax basis, even if your own contributions are Roth. That means the matching portion will be taxable when you withdraw it in retirement.
Vesting: When the Match Is Really Yours
Your own contributions are always 100% yours. Employer contributions come with strings. Federal law allows two vesting structures for employer money in an individual account plan:
- Cliff vesting: you own nothing of the match until you complete three years of service, then become fully vested all at once.
- Graded vesting: ownership grows gradually, reaching 20% after two years, 40% after three, 60% after four, 80% after five, and 100% after six.4Office of the Law Revision Counsel. 29 USC 1053 – Minimum Vesting Standards
Plans set up as qualified automatic contribution arrangements under SECURE 2.0 must fully vest employer contributions after just two years.5Internal Revenue Service. Retirement Topics – Automatic Enrollment If you leave before you’re vested, the unvested portion stays with the employer. When weighing a job offer, the vesting schedule matters as much as the match percentage.
How Much You Can Contribute in 2026
The IRS adjusts contribution ceilings annually for inflation. For 2026, you can defer up to $24,500 of your own pay.6Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
Older workers get extra room through catch-up contributions:
- Age 50 and older: an additional $8,000, for a total employee limit of $32,500.7Internal Revenue Service. Notice 2025-67 – 2026 Amounts Relating to Retirement Plans and IRAs
- Ages 60 through 63: a higher “super catch-up” of $11,250, for a total employee limit of $35,750.
When employer contributions are added, the combined total from all sources cannot exceed $72,000 before catch-ups. Catch-up contributions sit on top of that ceiling, so a 62-year-old who maxes out everything could shelter as much as $83,250 in a single year.7Internal Revenue Service. Notice 2025-67 – 2026 Amounts Relating to Retirement Plans and IRAs
One rule changes for high earners in 2026: if you earned more than $145,000 from your employer in the prior year, any catch-up contributions must go into the Roth side of the plan. The pre-tax catch-up option is gone for that group. The IRS provided a two-year transition period for this SECURE 2.0 provision, but it ends after 2025.8Internal Revenue Service. Guidance on Section 603 of the SECURE 2.0 Act with Respect to Catch-Up Contributions
Who Gets to Participate, and When
Federal law caps the barriers an employer can put between you and the plan. At most, a company can require you to turn 21 and complete one year of service.9Office of the Law Revision Counsel. 29 USC 1052 – Minimum Participation Standards Many employers let you in sooner. None can make you wait longer.
Part-time workers have a path in too. Under SECURE 2.0, if you log at least 500 hours in each of two consecutive 12-month periods and have reached age 21, the plan must let you participate. The threshold was three consecutive years originally; SECURE 2.0 shortened it to two, effective for plan years beginning after 2024.10Internal Revenue Service. Notice 2024-73 – Additional Guidance with Respect to Long-Term, Part-Time Employees
If your employer created its 401(k) after December 29, 2022, federal law now requires the plan to enroll you automatically. Your starting contribution rate will be set somewhere between 3% and 10% of pay and will rise by one percentage point each year until it reaches at least 10%, capped at 15%. You can always opt out or change the rate.5Internal Revenue Service. Retirement Topics – Automatic Enrollment Small businesses with 10 or fewer employees, companies less than three years old, church plans, and government plans are exempt.
Investing the Money and Watching the Fees
Once contributions land in your account, you choose how to invest them from a menu the plan provides. Most lineups include stock funds, bond funds, and a set of target-date funds that shift from aggressive to conservative as you approach a chosen retirement year. Low-cost index funds are a staple in most lineups.
The biggest mistake participants make is either ignoring the investment decision entirely and leaving everything in a default money market fund, or checking the balance so often that short-term dips prompt panic selling.
Fees deserve attention. Even half a percentage point in annual expenses can cost tens of thousands of dollars over a 30-year career. Federal regulations require your plan administrator to disclose plan-wide administrative costs, individual transaction fees, and the annual operating expenses of each investment option, expressed as a percentage and as a dollar amount per $1,000 invested.11eCFR. 29 CFR 2550.404a-5 – Fiduciary Requirements for Disclosure in Participant-Directed Individual Account Plans Your quarterly statement shows what was charged to your account. Read it.
Getting Money Out
A 401(k) is built for retirement, and the tax code enforces that with penalties for early access and requirements for eventual withdrawals.
Before Age 59½
Take money out of a traditional 401(k) before age 59½ and you owe income tax on the full amount plus a 10% early distribution penalty.12Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions Several exceptions waive the 10% penalty (but not the income tax):
- Rule of 55: if you leave your job during or after the year you turn 55, you can withdraw from that employer’s 401(k) penalty-free. Public safety employees get this at age 50.
- Total and permanent disability.
- A series of substantially equal periodic payments based on your life expectancy.
- Death, for the beneficiaries who inherit the account.
The Rule of 55 catches people off guard. It applies only to the 401(k) at the employer you just left. Money sitting in an old 401(k) from a previous job or in an IRA does not qualify.
Loans and Hardship Withdrawals
Many plans let you borrow from your own balance. The maximum loan is the lesser of $50,000 or 50% of your vested account balance. If 50% of your balance is under $10,000, some plans let you borrow up to $10,000, though they are not required to.13Internal Revenue Service. Retirement Topics – Loans You repay with interest, typically to yourself, through payroll deductions over up to five years (longer for a primary home purchase). If you leave the job with an outstanding balance, the plan can treat the unpaid amount as a distribution, triggering income tax and possibly the 10% penalty. You can avoid that by rolling the outstanding balance into an IRA or another eligible plan by the due date of your federal tax return, including extensions, for the year of the deemed distribution.
A hardship withdrawal is different: it’s not repaid. The IRS recognizes several situations that automatically qualify as an immediate and heavy financial need, including medical expenses, costs of buying your primary home (not mortgage payments), tuition and room and board for the next 12 months of post-secondary education, payments to prevent eviction or foreclosure, funeral expenses, and certain repairs to your primary home after damage.14Internal Revenue Service. Retirement Topics – Hardship Distributions Even when you qualify, the withdrawal is taxable and may carry the 10% penalty if you’re under 59½. You cannot take more than you actually need for the hardship. Not every plan offers hardship withdrawals.
Required Minimum Distributions
You cannot leave money in a traditional 401(k) indefinitely. Starting at age 73, you must begin taking required minimum distributions each year. The first one is due by April 1 of the year after you turn 73; every subsequent distribution must come out by December 31.15Internal Revenue Service. Retirement Topics – Required Minimum Distributions (RMDs) Delaying that first distribution to April creates a year with two RMDs, which can push you into a higher bracket.
There is one useful exception. If you are still working at the company that sponsors the plan and you do not own 5% or more of the business, you can delay RMDs from that specific plan until you actually retire.16Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs It does not apply to IRAs or to 401(k)s from former employers.
What Happens When You Leave the Job
You have four options for the balance at a former employer: leave it in the old plan (if it allows), roll it into your new employer’s 401(k), roll it into an IRA, or cash it out. Cashing out is almost always the worst choice because of taxes and penalties.
How you do a rollover matters. A direct rollover moves the funds straight from one plan to another without you touching the money. No withholding, no deadline pressure. An indirect rollover sends a check to you first, and the plan is required to withhold 20% for federal taxes. You then have 60 days to deposit the full original amount into the new account, including the 20% that was withheld (which you have to cover from other funds). Fall short or miss the deadline and the shortfall becomes a taxable distribution.17Internal Revenue Service. Rollovers of Retirement Plan and IRA Distributions The direct rollover avoids the entire problem.
Naming Your Beneficiary
Your 401(k) does not pass through your will. It goes to whoever is listed as beneficiary on file with the plan administrator. Skip that step or forget to update it after a marriage, divorce, or death in the family, and the account may end up in probate or with the wrong person. If you are married, federal law generally requires your spouse to be the primary beneficiary unless they sign a written waiver. Review the designation whenever your circumstances change.