What Is a 401(k)? Definition, Contribution Limits, and How It Works
Last updated 04/07/2026 by
Ante Mazalin
Edited by
Andrew Latham
Summary:
A 401(k) is an employer-sponsored retirement savings plan that lets employees contribute pre-tax (or after-tax Roth) income, reducing their taxable income today or in retirement.
It comes in two main forms, each with a different tax structure.
- Traditional 401(k): Contributions are pre-tax, reducing your taxable income now. Withdrawals in retirement are taxed as ordinary income — best if you expect to be in a lower tax bracket later.
- Roth 401(k): Contributions are made with after-tax dollars. Qualified withdrawals in retirement are completely tax-free — best if you expect to be in a higher tax bracket later.
- Employer match: Many employers match a percentage of employee contributions — free money that instantly boosts your return. Always contribute at least enough to capture the full match.
- Solo 401(k): Available to self-employed individuals and business owners with no full-time employees, with higher contribution limits than standard plans.
A 401(k) is often the single most powerful savings tool available to working Americans — but most people contribute too little, miss their employer match, or ignore the investment options inside the account.
Getting the basics right here has compounding consequences over decades.
How a 401(k) Works
Your employer sets up a 401(k) plan through a financial institution (Fidelity, Vanguard, Schwab, and Principal are among the largest providers). You elect to have a percentage of each paycheck directed into the account before taxes are calculated, reducing your taxable income for the year.
The money grows tax-deferred — meaning you pay no taxes on capital gains, dividends, or interest inside the account while it grows. You pay ordinary income tax when you withdraw the money in retirement (for traditional 401(k)s).
Investment options are set by your employer’s plan and typically include mutual funds, index funds, and target-date funds.
Unlike an IRA, you cannot invest in individual stocks or ETFs directly in most 401(k) plans — your choices are limited to what the plan offers.
2024 and 2025 401(k) Contribution Limits
| Category | 2024 Limit | 2025 Limit |
|---|---|---|
| Employee contribution limit (under 50) | $23,000 | $23,500 |
| Catch-up contribution (age 50–59, 64+) | $7,500 | $7,500 |
| Catch-up contribution (age 60–63, SECURE 2.0) | N/A | $11,250 |
| Total limit including employer contributions | $69,000 | $70,000 |
The IRS adjusts these limits annually for inflation. The SECURE 2.0 Act of 2022 introduced an enhanced catch-up for those aged 60–63 starting in 2025, allowing contributions of up to $34,750 — the highest 401(k) contribution opportunity available to any age group.
The Employer Match: The Most Important 401(k) Number
An employer match is the closest thing to a guaranteed return in personal finance.
If your employer matches 50% of contributions up to 6% of salary, contributing 6% of a $75,000 salary yields a $2,250 employer contribution on top of your $4,500 — a 50% instant return on that money.
The two most common match structures:
- Partial match: The employer matches a percentage of employee contributions up to a salary cap. Example: 50% match on up to 6% of salary.
- Dollar-for-dollar match: The employer matches every dollar you contribute, up to a limit. Example: 100% match on up to 4% of salary.
Vesting schedules determine when the employer’s contributions become fully yours. Some plans vest immediately; others use a cliff schedule (fully vested after 3 years) or graded schedule (20% per year over 5 years).
Leaving before fully vested means forfeiting unvested employer contributions.
Pro Tip: If you can’t afford to max your 401(k), at minimum contribute enough to capture the full employer match before directing any savings elsewhere. Failing to get the full match is the equivalent of voluntarily declining part of your salary.
Traditional 401(k) vs. Roth 401(k)
| Feature | Traditional 401(k) | Roth 401(k) |
|---|---|---|
| Contributions | Pre-tax (reduces taxable income now) | After-tax (no immediate tax benefit) |
| Tax on growth | Tax-deferred | Tax-free |
| Tax on withdrawals | Taxed as ordinary income | Tax-free (if qualified) |
| Required Minimum Distributions | Yes, starting at age 73 | No longer required (post-SECURE 2.0) |
| Best for | Higher earners expecting lower tax bracket in retirement | Younger earners expecting higher tax bracket later |
401(k) Withdrawal Rules
Withdrawing from a 401(k) before age 59½ typically triggers a 10% early withdrawal penalty plus ordinary income tax on the amount withdrawn — a costly combination. A $20,000 early withdrawal in the 22% tax bracket costs $6,400 in taxes and penalties before the money reaches your hands. See the full guide to 401(k) withdrawals for exceptions and strategies.
Exceptions to the 10% penalty include:
- Separation from service at age 55 or older (Rule of 55)
- Substantially equal periodic payments (SEPP/Rule 72(t))
- Total and permanent disability
- Death (distributions to beneficiaries)
- Qualified domestic relations order (divorce settlements)
- Unreimbursed medical expenses exceeding 7.5% of AGI
Starting at age 73, the IRS requires Required Minimum Distributions (RMDs) from traditional 401(k) accounts — minimum annual withdrawals calculated based on your account balance and IRS life expectancy tables. Failing to take RMDs triggers a 25% excise tax on the amount that should have been withdrawn.
How to choose 401(k) investments
Follow these steps to build a sensible 401(k) investment strategy:
- Start with a target-date fund if in doubt. Target-date funds automatically rebalance from growth-oriented to conservative as your retirement year approaches. The 2060 fund is appropriate for someone retiring around 2060.
- Check the expense ratios. Even a 0.5% difference in annual fees compounds dramatically over 30 years. Favor index funds with expense ratios below 0.10% over actively managed funds charging 0.75% or more.
- Diversify across asset classes. A basic three-fund portfolio — U.S. stocks, international stocks, and bonds — captures broad market returns with minimal complexity.
- Adjust equity allocation by age. A common rule: subtract your age from 110 to get your stock allocation. At 35, that suggests 75% equities; at 60, 50% equities.
- Rebalance annually. Once per year, return your portfolio to its target allocation by selling outperformers and buying underperformers.
What Happens to Your 401(k) When You Leave a Job?
When you leave an employer, you have four options for your 401(k):
- Roll over to new employer’s plan: Maintains tax-deferred status; limits you to the new plan’s investment options.
- Roll over to an IRA: Expands investment choices and consolidates accounts; most common choice for maximum flexibility. Read more about how to roll a 401(k) into an IRA.
- Leave in former employer’s plan: Permitted if balance exceeds $5,000; may limit service options over time.
- Cash out: Available but almost always inadvisable — triggers income tax plus 10% early withdrawal penalty if under 59½.
Key takeaways
- A 401(k) is an employer-sponsored retirement plan with tax-advantaged contributions — either pre-tax (traditional) or after-tax (Roth).
- The 2025 employee contribution limit is $23,500, with a $7,500 catch-up for those 50+, and $11,250 for those aged 60–63.
- Always contribute at least enough to capture the full employer match — it’s an immediate 50–100% return on that contribution.
- Early withdrawals before age 59½ trigger a 10% penalty plus income tax, making them one of the most expensive financial moves available.
- Traditional 401(k)s require minimum distributions starting at age 73; Roth 401(k)s no longer require RMDs (post-SECURE 2.0).
- When leaving a job, rolling over to an IRA typically provides the most investment flexibility.
Frequently Asked Questions
What is the difference between a 401(k) and an IRA?
A 401(k) is sponsored by your employer, has higher contribution limits ($23,500 in 2025), and limits investment choices to options within your plan.
A traditional IRA is opened individually, has lower limits ($7,000 in 2025), but offers broader investment flexibility including stocks, bonds, ETFs, and mutual funds. Many people use both accounts simultaneously.
How much should I contribute to my 401(k)?
Financial planners generally recommend saving 10–15% of gross income for retirement across all accounts. At minimum, contribute enough to receive the full employer match. If you can increase to the maximum contribution limit, the tax deferral and compound growth over decades is significant.
Can I have a 401(k) and a Roth IRA at the same time?
Yes. Contributing to a 401(k) does not affect your ability to contribute to a Roth IRA, provided your income falls below the Roth IRA income limits ($161,000 for single filers and $240,000 for married filing jointly in 2024). See our 401(k) vs. Roth IRA comparison for help deciding how to split contributions.
What is a safe harbor 401(k)?
A safe harbor 401(k) is a plan design that automatically satisfies certain IRS non-discrimination testing requirements by requiring the employer to make a minimum contribution for all eligible employees — either a 3% non-elective contribution or a matching contribution. In exchange, the plan is exempt from annual testing that limits how much highly compensated employees can contribute.
What happens to my 401(k) if my employer goes bankrupt?
401(k) assets are held in a trust separate from the company’s assets and are protected from employer creditors. Your money is not at risk if your employer goes bankrupt. However, you may need to roll the funds into an IRA or a new employer’s plan, as the plan may be terminated during bankruptcy proceedings.
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