How a 401(k) Works: Contributions, Growth, and Withdrawals

How money moves through your 401(k)

A 401(k) is an employer-sponsored retirement account where you contribute money from your paycheck before taxes are taken out, your employer may add matching contributions, and the money grows tax-deferred until you withdraw it in retirement. Your employer sets up the plan with a financial institution (often called the plan administrator or custodian), chooses which investments you can pick from, and handles the payroll deductions. You decide how much to contribute each year, which investments to hold, and when to rebalance them.

The money you contribute reduces your taxable income for that year. If you earn $60,000 and contribute $7,000 to your 401(k), you pay income tax only on $53,000. The $7,000 grows inside the account without triggering capital gains tax each year, and you do not owe income tax on those gains until you take the money out—usually in retirement.

Your employer may match a portion of what you contribute. A common match is 50 cents for every dollar you contribute, up to 6% of your salary. If you earn $50,000 and contribute 6% ($3,000), your employer adds $1,500. That match is assistance programs and vests according to a schedule your employer sets—usually over three to five years. Once vested, it belongs to you even if you leave the job.

Key Takeaways

• You contribute pre-tax dollars from your paycheck, which lowers your taxable income for the year.
• Your employer may match part of your contribution, and that match typically vests over three to five years.
• The annual contribution limit is set by the IRS and changes yearly; for 2024 it is $23,500 for people under 50.
• You choose how to invest the money from a menu your employer provides, and investment gains are not taxed until withdrawal.
• Withdrawals before age 59½ usually trigger a 10% penalty plus income tax, with limited exceptions for hardship or loans.

Annual contribution limits and catch-up contributions

The IRS sets a maximum amount you can contribute to your 401(k) each year. For 2024, that limit is $23,500 if you are under age 50. The limit increases most years to keep pace with inflation, but the increase happens only in $500 increments, so it does not change every year. Your employer's payroll system should prevent you from contributing more than the limit, but it is your responsibility to track contributions across multiple employers if you have changed jobs during the year.

If you are age 50 or older, you can make an additional catch-up contribution of $7,500 per year, bringing your total to $31,000 for 2024. This rule exists to help people who started saving later or want to accelerate retirement savings in their final working years. The catch-up limit also adjusts for inflation in $500 increments.

Your employer's match does not count toward your personal contribution limit. If your employer matches $5,000 and you contribute $23,500, you have hit the limit, but the employer can still add the full match on top of that. However, the combined total of employee and employer contributions cannot exceed $69,000 for 2024 (or $76,500 if you are 50 or older and making catch-up contributions).

How investment choices work inside your 401(k)

Your employer selects a menu of investment options—typically mutual funds, index funds, target-date funds, and sometimes individual stocks or company stock. You direct how much of your balance goes into each option. The plan administrator holds the money and executes the trades; you do not buy or sell directly. Most plans let you change your investment mix online or through a phone line, and many allow changes as often as daily, though most people rebalance only once or twice a year.

A target-date fund is a popular choice for people who do not want to pick individual investments. You choose a fund based on your expected retirement year—for example, a 2050 target-date fund if you plan to retire around 2050. The fund manager automatically shifts the mix from stocks (which grow faster but fluctuate more) toward bonds (which are more stable) as your target date approaches. This removes the need to rebalance manually.

Investment gains, dividends, and interest earned inside your 401(k) are not taxed each year the way they would be in a regular brokerage account. That tax deferral is one of the main advantages of a 401(k). You pay income tax on all withdrawals in retirement, whether the money came from your contributions or from investment growth.

Vesting: when employer contributions become yours

Your own contributions are always yours immediately—you are 100% vested in them from day one. Employer matching contributions, however, vest on a schedule set by your employer. The most common schedule is graded vesting, where you become vested in a percentage of the match each year. For example, a three-year graded schedule might vest you 33% per year, so after three years you own 100% of all employer contributions.

Some employers use cliff vesting, where you own 0% of the employer match until you hit a specific date—often three or five years—at which point you own 100%. If you leave before the cliff date, you forfeit the unvested match. The forfeited money stays in the plan and is used to reduce future employer contributions or cover plan expenses.

Your vesting schedule is spelled out in your plan's Summary Plan Description (SPD), a document your employer must provide. If you change jobs, check your vesting status before you leave. If you are close to vesting, staying a few more months might be worth thousands of dollars.

Withdrawals before retirement and the 10% penalty

If you withdraw money from your 401(k) before age 59½, you owe income tax on the withdrawal plus a 10% early withdrawal penalty. If you withdraw $10,000 at age 45 and are in the 24% tax bracket, you owe $2,400 in income tax plus $1,000 in penalty—leaving you $6,600 of the original $10,000. That penalty is steep, which is why 401(k)s are designed as long-term retirement accounts.

The IRS allows a few exceptions to the 10% penalty (though not the income tax). These include withdrawals for a may have access to hardship (defined narrowly by the IRS—typically medical bills, home purchase, or preventing eviction), withdrawals under the CARES Act (a temporary rule from 2020 for COVID-related hardship), and withdrawals if you leave your job in the year you turn 55 or later. Some plans also allow loans against your balance, where you borrow from yourself and repay with interest; loans do not trigger the penalty as long as you repay on schedule.

At age 59½, you can withdraw money without the 10% penalty, though you still owe income tax. At age 73, the IRS requires you to take Required Minimum Distributions (RMDs) each year based on your age and account balance. If you do not take the RMD, the IRS charges a 25% penalty on the amount you should have withdrawn (reduced to 10% if you correct it within two years).

Rolling over a 401(k) when you change jobs

When you leave a job, you have several choices for your 401(k) balance. You can leave it in your former employer's plan (if the balance is above a minimum, often $5,000), roll it into your new employer's plan (if the new plan accepts rollovers), or roll it into an Individual Retirement Account (IRA). A rollover moves money from one account to another without triggering taxes or penalties, as long as you follow the rules.

A direct rollover is the safest method: the plan administrator sends the money directly to the new account in your name. You never touch the money, so there is no tax withholding and no risk of missing a deadline. A indirect rollover sends the check to you, and you have 60 days to deposit it into another retirement account. The plan administrator withholds 20% for federal taxes, so if your balance is $50,000, you receive $40,000 and must deposit the full $50,000 within 60 days to avoid taxes and penalties on the $10,000 shortfall. Most people choose direct rollover to avoid this complication.

Rolling into an IRA gives you more investment choices than most 401(k) plans offer, but you lose the option to borrow against the balance and may face higher fees depending on the IRA provider. Rolling into a new employer's plan keeps everything in the 401(k) system and may simplify record-keeping if you have multiple old plans.

Tax treatment: pre-tax contributions and Roth options

Most 401(k) contributions are pre-tax, meaning they reduce your taxable income in the year you contribute. You pay income tax on withdrawals in retirement. This lowers your tax bill now but means you owe tax on the full amount you withdraw later, including all investment gains.

Some employers also offer a Roth 401(k) option. Roth contributions do not reduce your taxable income this year, but withdrawals in retirement are tax-free—including all investment gains. The choice between pre-tax and Roth depends on whether you expect to be in a higher or lower tax bracket in retirement. If you expect lower income in retirement, pre-tax contributions save you more tax now. If you expect higher income or think tax rates will rise, Roth contributions may save you more tax over your lifetime.

You can split contributions between pre-tax and Roth in the same year. For example, you might contribute $15,000 pre-tax and $8,500 Roth, totaling $23,500 for 2024. The employer match, if any, is always pre-tax and goes into the pre-tax side of the account.

Understanding fees and how they affect your balance

401(k) plans charge fees that reduce your account balance over time. These include plan administration fees (charged by the plan administrator for record-keeping and compliance), investment fees (charged by the mutual funds or index funds you hold), and sometimes individual service fees (charged for loans, rollovers, or other services). Your plan's Summary Plan Description and annual statements should disclose these fees, though the disclosure is often buried in dense language.

Investment fees are expressed as an expense ratio—the percentage of your balance charged annually. A fund with a 0.05% expense ratio on a $100,000 balance costs $50 per year. A fund with a 1% expense ratio costs $1,000 per year on the same balance. Over decades, that difference compounds significantly. Index funds and target-date funds typically have lower expense ratios than actively managed funds.

Some employers offer low-cost plans with total fees under 0.5% annually, while others charge 1.5% or more. If your plan's fees seem high, ask your HR department for a fee breakdown. Many plans have improved their offerings in recent years due to regulatory pressure, so older plans may have higher-cost options than newer ones.

Frequently Asked Questions

Can I contribute to a 401(k) and an IRA in the same year?

Yes. Your 401(k) contribution limit and IRA contribution limit are separate. You can contribute up to $23,500 to a 401(k) and up to $7,000 to an IRA in 2024 (or $8,000 if you are 50 or older). However, if you have a traditional IRA and earn above a certain income threshold, your pre-tax IRA contributions may not be tax-deductible. Check the IRS rules for your income level.

What happens to my 401(k) if I am laid off or fired?

Your 401(k) balance belongs to you and remains in the account. You cannot access it penalty-free until age 59½ unless you meet an exception, but you can roll it into an IRA or your new employer's plan. Any unvested employer match is forfeited and returned to the plan. Your vested balance is always yours to keep or move.

Can I borrow from my 401(k)?

Many plans allow loans up to 50% of your vested balance or $50,000, whichever is less. You repay the loan with interest (set by your plan, typically prime rate plus 1%) over five years or longer if the loan is for a home purchase. Loans do not trigger the 10% penalty, but if you leave your job before repaying, the unpaid balance is treated as a withdrawal and taxed plus penalized.

What is the difference between a 401(k) and a 403(b)?

A 403(b) is similar to a 401(k) but is offered by schools, nonprofits, and some government employers instead of for-profit companies. Contribution limits and tax treatment are the same, but 403(b) plans often have fewer investment options and different fee structures. The rules for withdrawals, loans, and rollovers are also largely the same.

Do I have to take money out of my 401(k) at retirement?

Not immediately. You can leave the money in your 401(k) and continue to defer taxes as long as you are still employed by that company (though some plans require withdrawal after you retire). At age 73, the IRS requires you to take Required Minimum Distributions based on your age and balance. If you roll the 401(k) into an IRA, RMDs still apply at age 73.