How a 401(k) Works | The Financial Compass

13 min readUpdated September 26, 2026

A 401(k) is one of the main ways Americans save for retirement through work.

You contribute part of your paycheck. Your employer may add money too. You then choose from the investments available inside the plan, and the account can grow over time.

The tax treatment depends on whether you use a traditional 401(k), Roth 401(k), or a combination of both.

The basic idea is straightforward. The details matter. This guide walks through those details; for the wider picture, see the Retirement section.

What Is a 401(k)?

A 401(k) is an employer-sponsored retirement plan.

Employees can direct part of their wages into an individual retirement account inside the employer’s plan. The money can then be invested in choices provided by the plan.

Depending on the employer, those choices might include:

stock mutual funds
bond funds
index funds
target-date retirement funds
stable-value or cash-like options
company stock in some plans

Your employer decides which investment options the plan offers.

You decide how much to contribute, subject to IRS limits, and usually decide how to invest the money.

How Contributions Work

Suppose you earn $70,000 a year and decide to contribute 8 percent of your salary.

That works out to:

$70,000 × 8% = $5,600 per year

If you are paid every two weeks, part of that $5,600 will normally be deducted from each paycheck and deposited into your 401(k).

Once the money reaches the account, it gets invested according to your instructions.

Many plans also let you change your contribution percentage later.

Some employers automatically enroll eligible workers unless they opt out or select a different contribution rate.

Traditional 401(k) vs Roth 401(k)

Many plans now offer both traditional and Roth contributions.

The main difference is when you pay income tax. It mirrors the same choice that separates a traditional IRA from a Roth IRA.

Traditional 401(k)

Traditional 401(k) contributions are generally made on a pre-tax basis for federal income tax purposes.

Suppose you earn $80,000 and contribute $8,000 to a traditional 401(k).

Your federal taxable income may generally be reduced by that contribution, subject to applicable tax rules.

The money then grows tax-deferred inside the account.

When you withdraw taxable money in retirement, those withdrawals are generally included in your taxable income.

You receive the tax break today and generally pay tax later.

Roth 401(k)

Roth 401(k) contributions work differently.

You make contributions with after-tax money, so they do not generally reduce your current federal taxable income.

The potential benefit comes later.

Qualified Roth 401(k) distributions can be tax-free if the requirements are met. In general, a qualified distribution must occur after the required five-year period and after age 59½, disability, or death.

You pay the income tax now and may receive qualified withdrawals tax-free later.

Can You Use Both?

If your employer offers both options, you may be able to divide your contributions between traditional and Roth 401(k) accounts.

For example:

Traditional 401(k): $600 per month
Roth 401(k): $400 per month

Your total employee contribution would be $1,000 per month.

Using both can give you two different types of tax treatment in retirement.

The same annual employee contribution limit applies across your traditional and Roth 401(k) contributions combined.

2026 401(k) Contribution Limits

For 2026, the standard employee elective deferral limit for most 401(k) plans is:

$24,500

This is the combined limit for traditional and Roth employee contributions.

If you participate in more than one 401(k) or similar employer plan during the year, the employee limit generally applies across those plans rather than separately to each one.

Catch-Up Contributions

People age 50 or older may be able to contribute additional money if their plan permits catch-up contributions.

For 2026, the general catch-up limit is:

$8,000

That means many eligible workers age 50 or older could contribute up to:

$32,500

Employees who are ages 60, 61, 62, or 63 during 2026 can qualify for a higher catch-up limit of:

$11,250

That could bring their employee contribution total to:

$35,750

Beginning in 2026, certain higher-paid workers making catch-up contributions must make those catch-up contributions on a Roth basis. For 2026, the IRS says this rule applies when prior-year wages from the plan sponsor exceeded $150,000, subject to the plan and applicable rules.

Contribution limits change over time, so check the current IRS limit each year.

The Total 401(k) Limit Is Higher

The $24,500 limit applies mainly to your own elective salary deferrals.

Employer contributions are counted under a separate overall limit.

For 2026, total annual additions to most defined contribution accounts generally cannot exceed the lesser of:

100 percent of eligible compensation

$72,000

Catch-up contributions can sit above that basic $72,000 limit for eligible participants.

Most workers will never come close to this overall limit, but it matters when employers make substantial contributions or when someone has access to certain after-tax contribution arrangements.

How an Employer Match Works

An employer match is one of the most valuable features a 401(k) can offer.

Your employer contributes money based on how much you contribute.

The formula varies.

Suppose your employer matches:

50 cents for every $1 you contribute, up to 6 percent of your salary.

You earn $60,000.

Six percent of your salary is:

$3,600

If you contribute $3,600, your employer contributes:

$1,800

Your total contribution for the year becomes:

$5,400

You contributed $3,600.

Your employer added $1,800.

The IRS allows employers to make matching contributions when the plan provides for them.

Understand the Match Formula

Employers use different formulas.

One might offer:

100% match on the first 3% of salary

Another might offer:

50% match on the first 6%

Another company may make an employer contribution whether you contribute or not.

Read your plan documents rather than assuming the match works the same way as a previous employer’s plan.

Pay attention to contribution limits per paycheck too.

Some plans calculate matches each pay period. If you contribute heavily early in the year and stop later, the timing could affect the match unless the employer provides a year-end “true-up.”

Your plan administrator can explain how your specific formula works.

What Does Vesting Mean?

Vesting determines how much of the money in your account you legally own.

Your own salary contributions are always 100 percent vested.

If you contribute $10,000 and later leave your employer, that money remains yours, along with investment gains or losses attached to it.

Employer contributions can work differently.

Some are immediately vested.

Others may become yours gradually.

For example, a hypothetical plan might vest employer contributions like this:

Years of Service	Employer Money You Own
1 year	0%
2 years	25%
3 years	50%
4 years	75%
5 years	100%

If you leave before becoming fully vested, you could lose the unvested portion of employer contributions.

Your employer’s actual schedule may differ.

Safe harbor 401(k) plans generally require certain employer contributions to be fully vested when made, while traditional 401(k) plans may use vesting schedules.

Your 401(k) Is an Account, Not an Investment

This distinction matters.

A 401(k) is the account.

You still need to choose investments inside it.

Simply contributing money does not tell you how that money will be invested.

Depending on the plan, you might choose among:

U.S. stock funds
international funds
bond funds
target-date funds
money market or stable-value options

Two employees contributing exactly the same amount can have very different investment results because they choose different investments.

Target-Date Funds

Many 401(k) plans offer target-date retirement funds.

A target-date fund generally holds a mix of investments and gradually changes that mix as its target retirement year approaches.

Someone expecting to retire around 2060 might consider a 2060 target-date fund.

These funds can simplify portfolio management because asset allocation and rebalancing happen inside the fund.

Still, compare the fund’s:

stock and bond allocation
expense ratio
investment strategy
glide path
underlying holdings

Two target-date funds with the same year can take different levels of risk.

Your Investment Mix Matters

A worker in their 20s with several decades before retirement may be willing to hold a larger percentage of stocks.

Someone close to retirement may want a different balance between stocks, bonds, and cash-like investments.

This is asset allocation.

Your mix should reflect your timeframe, financial situation, and ability to tolerate market losses.

A 401(k) gives you tax advantages.

It does not protect you from investment losses.

Compounding Inside a 401(k)

One advantage of starting early is time.

Imagine investing $500 each month.

At first, most of your account comes from contributions.

Over time, investment returns can begin generating returns of their own.

That is compounding.

The longer the money remains invested, the more time compounding has to work.

This is why a worker who starts contributing in their 20s or 30s can have a major advantage over someone who waits until much later, even if the later investor eventually contributes more each month.

Your actual results depend on investment returns, fees, contribution amounts, taxes, and market conditions.

What Happens When Investments Fall?

Your 401(k) balance can decline.

If you hold stock funds and the market falls sharply, the value of those investments may fall too.

This does not mean the 401(k) itself has failed.

The account reflects the performance of the investments inside it.

If you continue contributing during a decline, your regular contribution may buy more shares at lower prices.

For workers with long time horizons, short-term market volatility is often part of the investing process.

Watch Your 401(k) Fees

Fees can quietly reduce long-term results.

401(k) plans may include:

investment management fees
plan administration fees
individual service fees
expenses charged by specific funds

The Department of Labor warns that fees and expenses reduce the amount of investment return that remains in your retirement account. Even relatively small annual differences can become meaningful over a long investing period.

Check each fund’s expense ratio and review the fee information provided by your plan.

Lower cost alone does not automatically make a fund better.

But you should know what you are paying.

Can You Withdraw Money From a 401(k) Early?

A 401(k) is designed for retirement.

Access before retirement can therefore be restricted.

Many plans allow distributions after certain events such as:

leaving the employer
reaching age 59½
disability
qualifying hardship
other events permitted under the plan

Specific rules depend on the plan.

The 10% Additional Tax

If you take a taxable distribution before age 59½, you may owe ordinary income tax plus an additional 10 percent federal tax.

There are exceptions.

For example, certain distributions related to disability, death, qualifying medical expenses, court orders, or separation from service after reaching a qualifying age may avoid the additional tax.

The rules can become complicated.

Do not assume a hardship withdrawal automatically avoids the 10 percent additional tax. The IRS notes that hardship distributions can still be subject to it unless an exception applies.

What About 401(k) Loans?

Some plans allow you to borrow from your account.

A loan can provide temporary access to retirement money without immediately treating the amount as a taxable withdrawal, provided you follow the applicable rules.

But borrowing from retirement savings has costs.

Money taken out of investments may miss market growth.

Repayments affect your cash flow.

If you fail to repay according to the rules, part of the loan may become a taxable distribution.

Your plan is not required to offer loans, so check the plan documents before assuming this option exists.

What Happens When You Leave Your Job?

Leaving your employer does not mean your 401(k) disappears.

The IRS outlines several common options.

You may be able to:

leave the account in your former employer’s plan
roll it into your new employer’s eligible retirement plan
roll it into an IRA
withdraw the money

Each choice has different consequences.

Be Careful About Cashing Out

Cashing out a 401(k) when changing jobs can be expensive.

Suppose you have $40,000 in a traditional 401(k).

You withdraw it rather than rolling it over.

The taxable amount may be included in your income, and if you are below the applicable age and no exception applies, you may also face the additional 10 percent early-distribution tax.

You also remove $40,000 from your retirement savings.

That money loses the opportunity to remain invested for retirement.

Direct Rollovers Can Simplify the Process

If you move retirement money to another eligible plan or IRA, a direct rollover is often simpler than having the money paid to you personally.

With a direct transfer, the funds generally move from one retirement account to another without federal income tax withholding.

If an eligible distribution is paid directly to you instead, the plan will generally withhold 20 percent for federal income taxes. You would normally need to replace the withheld amount from other money if you want to roll over the full distribution within the allowed period.

Required Minimum Distributions

Traditional 401(k) money generally cannot remain sheltered from distributions indefinitely.

Under current federal rules, many retirement account owners must begin required minimum distributions at age 73, subject to rules based on birth year, employment status, plan terms, and ownership of the employer.

Current rules differ for Roth 401(k) accounts.

Designated Roth accounts in 401(k) plans are no longer subject to lifetime required minimum distributions for the original account owner. Beneficiaries remain subject to distribution rules.

Retirement distribution rules have changed several times in recent years, so check the latest IRS guidance as you approach retirement.

How Much Should You Contribute?

There is no single percentage that works for everyone.

Your contribution needs to fit alongside:

housing expenses
emergency savings
debt payments
insurance
other financial goals
everyday living costs

One practical starting point is to understand your employer match.

If an employer matches contributions up to a certain level, know exactly what you need to contribute to receive the available match.

From there, you can consider gradually increasing your savings rate as your income and budget allow. For a sense of the target you are working toward, see our guide to how much money you need to retire.

Consider Increasing Contributions After a Raise

Suppose you contribute 6 percent today.

You receive a raise next year.

Instead of allowing the entire raise to flow into spending, you might increase your 401(k) contribution to 7 percent.

Later, you might move to 8 percent.

Small increases can add up over a long career without requiring a dramatic change to your monthly budget.

Some plans offer automatic contribution escalation that increases your savings rate periodically unless you opt out.

Common 401(k) Mistakes

Contributing Without Checking the Investments

Money inside the account still needs to be invested appropriately.

Review what your contributions are actually buying.

Ignoring the Employer Match

Understand the formula and how much you need to contribute to qualify for the available match.

Forgetting About Old 401(k)s

Job changes can leave retirement accounts scattered across former employers.

Keep records of every account.

Paying No Attention to Fees

High expenses can reduce long-term growth.

Review both plan-level costs and investment expenses.

Taking Early Withdrawals Without Understanding the Cost

Taxes, possible penalties, and lost compounding can make early withdrawals expensive.

Changing Investments Because Markets Fall

Selling after a major decline can turn temporary market losses into permanent ones.

Review whether your asset allocation still fits your plan rather than reacting to frightening headlines.

A Simple 401(k) Example

Suppose Maria earns $75,000 a year.

She contributes 8 percent:

$6,000 per year

Her employer matches 50 percent of contributions up to 6 percent of salary.

Six percent of $75,000 is:

$4,500

The employer matches half:

$2,250

Total annual contributions:

$8,250

Maria then invests those contributions in the funds she selected inside the plan.

Over time, her account balance reflects:

her contributions + employer contributions + investment gains or losses − fees and withdrawals

That is the basic engine of a 401(k).

The Bottom Line

A 401(k) lets you save and invest for retirement through your employer.

Your own contributions come from your paycheck. Your company may provide matching or other employer contributions. The money can then grow inside the account according to the investments you choose.

Traditional contributions can provide a current income-tax benefit, with taxable withdrawals generally coming later.

Roth contributions use after-tax money and can provide tax-free qualified withdrawals.

For 2026, most employees can contribute up to $24,500, with additional catch-up contributions available to eligible older workers.

Understand your employer match.

Check the vesting schedule.

Choose investments deliberately.

Watch the fees.

And resist treating retirement savings like an everyday bank account.

Time can do a lot of the heavy lifting when you give it enough years.

Sources and further reading

401(k) tax rules, contribution limits, withdrawal rules, and plan features can change. Individual plans also differ. The Financial Compass provides educational information, not individualized investment, tax, or retirement advice.