What Is a 401k? Definition, Contribution Limits & How It Works

A 401k is a retirement savings plan your employer offers, named after section 401(k) of the Internal Revenue Code. You contribute a portion of your paycheck before taxes are taken out, and that money grows tax-deferred until you withdraw it in retirement.

The account is yours—you choose how much to contribute (up to IRS limits) and how to invest the money, typically selecting from a menu of mutual funds, index funds, target-date funds or bonds your plan offers.

Because contributions come out pre-tax, your taxable income drops by the amount you contribute. If you earn $60,000 and contribute $6,000, you only pay federal income tax on $54,000 that year.

Your contributions are invested according to the allocations you choose. Over time, those investments generate returns—dividends, interest, capital gains—and all growth is tax-deferred.

These limits apply to traditional 401k and Roth 401k contributions combined. If your plan offers both, your total deferrals cannot exceed $23,500 (or $31,000 with catch-up).

Many employers offer a 401k match—they contribute additional money to your account based on how much you put in. Common formulas include:

• 50% match on the first 6% of salary you contribute.
• Dollar-for-dollar match on the first 3% of salary.
• 100% match on the first 4%, then 50% on the next 2%.

Example: You earn $50,000 and your employer matches 50% of the first 6%. If you contribute 6% ($3,000), your employer adds $1,500—a guaranteed 50% return before any investment growth.

Vesting determines how much of your employer's contributions you actually own if you leave the company. Your own contributions are always 100% vested immediately.

Employer match typically follows one of two schedules:

• Cliff vesting: 0% until year three, then 100% all at once.
• Graded vesting: 20% per year over five years.

Most plans now offer both a traditional and a Roth 401k option. The contribution limits are the same, but the tax treatment differs:

Choose traditional if you expect to be in a lower tax bracket in retirement. Choose Roth if you expect higher future tax rates or want tax-free income later.

• Step 1: Contact your HR department or benefits administrator and request enrollment materials.
• Step 2: Decide your contribution rate.
• Step 3: Choose your investment allocations.
• Step 4: Designate beneficiaries.
• Step 5: Review and increase contributions annually.

Exceptions to the 10% penalty include:

• Separation from service at age 55 or later (the "rule of 55").
• Total and permanent disability.
• Substantially equal periodic payments (SEPP / 72(t) distribution).
• Qualified domestic relations order (divorce).
• Unreimbursed medical expenses exceeding 7.5% of AGI.

After age 59½, you can withdraw penalty-free, but you still owe ordinary income tax (except on Roth contributions). At age 73, required minimum distributions (RMDs) begin—you must withdraw a calculated percentage each year or face a 25% penalty on the shortfall.

Key risks:

• You lose compounding on the borrowed amount.
• If you leave your job, the full balance is usually due within 60–90 days, or the IRS treats it as a taxable distribution plus 10% penalty.
• Loan repayments are made with after-tax dollars, and you will pay tax again when you withdraw in retirement (double taxation on that portion).

Use a 401k loan only for true emergencies—never for discretionary purchases. Explore other options in our [money and debt](/money-and-debt) guides first.

1. 1Leave it in the old plan (if balance exceeds $7,000 and the plan allows).
2. 2Roll it into your new employer's 401k (if the new plan accepts rollovers).
3. 3Roll it into an IRA (traditional or Roth). This gives you unlimited investment options and often lower fees.
4. 4Cash out (taxable distribution + 10% penalty if under 59½—almost always a bad choice).

Direct rollover (trustee-to-trustee transfer) avoids withholding and tax complications. If you receive a check, 20% is withheld for taxes, and you have 60 days to deposit the full amount into a new qualified account or face tax and penalty.

Your plan offers a curated menu of investments, typically:

• Target-date funds: All-in-one portfolios that automatically shift from stocks to bonds as you approach retirement.
• Index funds: Low-cost funds tracking the S&P 500, total stock market or international indexes.
• Mutual funds: Actively managed stock or bond funds (usually higher expense ratios).
• Stable value or money-market funds: Low-risk, low-return options for capital preservation.
• Company stock: Some plans allow you to buy your employer's stock (usually not recommended due to concentration risk).

Not contributing enough to get the full match. If your employer matches 4% and you contribute only 2%, you are leaving 2% on the table every year—thousands of dollars of free money.

Cashing out when changing jobs. A $20,000 distribution at age 35 costs you $2,000 in penalty, $4,000–6,000 in tax, and roughly $100,000 in foregone growth by age 65.

Taking loans for non-emergencies. Borrowing $10,000 to buy a boat means you miss the compounding on that $10,000, often costing you $30,000–50,000 in retirement wealth.

Stopping contributions during market downturns. Dollar-cost averaging through a bear market buys shares at lower prices, which magnifies gains during recovery.

Key advantages:

• Tax-deferred growth (or tax-free with Roth).
• Employer match delivers an instant return.
• High contribution limits ($23,500 in 2026) compared to IRAs ($7,000 limit).
• Automatic payroll deduction removes the temptation to spend.
• Creditor protection under ERISA in most states.

Disadvantages:

• Limited investment menu.
• Early-withdrawal penalties lock up your money.
• Required minimum distributions force taxable income in retirement.
• Plan fees can be high (especially in small-company plans).

A 401k is one piece of a diversified retirement plan. Pair it with:

• IRA (traditional or Roth): Contribute $7,000/year ($8,000 if 50+) for more investment flexibility.
• HSA (health savings account): Triple tax advantage if you have a high-deductible health plan; can function as a stealth retirement account.
• Taxable brokerage account: No contribution limits or withdrawal penalties; useful for early-retirement plans or goals before age 59½.
• Real estate or business income: Diversify beyond paper assets.

Calculate how much you need to retire using the 4% rule: multiply your desired annual retirement spending by 25. If you want $60,000/year, you need $1.5 million saved.

What is a 401k and how does it work for beginners?

Can I have a 401k and an IRA at the same time?

Yes. You can contribute to both, but your IRA deduction may be reduced or eliminated if you (or your spouse) are covered by a 401k and your income exceeds certain thresholds ($77,000–$87,000 single, $123,000–$143,000 married filing jointly in 2026 for traditional IRA).

What happens to my 401k if I quit my job?

You keep the account—it is yours. You can leave the money in the old plan (if balance exceeds $7,000), roll it into your new employer's 401k, roll it into an IRA for more investment choices, or cash it out (which triggers taxes and penalties if under age 59½).

What is the difference between a 401k and a pension?

How much should I contribute to my 401k each month?

At minimum, contribute enough to capture your full employer match (often 3–6% of salary). If you want to retire comfortably, aim for 15–20% of gross income across all retirement accounts (401k + IRA + HSA).