What Is a 401(k)? Retirement Plans and Contribution Rules

What Is a 401(k)?

A 401(k) is an employer-sponsored, tax-advantaged retirement savings plan available to employees in the United States. The name comes from Section 401(k) of the Internal Revenue Code, which established these plans in 1978. Participants contribute a portion of their pre-tax salary into the account, where funds can grow through investments in stocks, bonds, and mutual funds — generally tax-deferred until withdrawal in retirement.

401(k) plans have become the dominant private-sector retirement vehicle in the U.S., largely replacing traditional pension plans since the 1980s. As of 2024, Americans hold approximately $7 trillion in 401(k) assets across more than 600,000 plans.

Traditional vs. Roth 401(k)

Two main variants of the 401(k) exist, differing in when taxes are applied.

Many employers offer both options, and employees can split contributions between them. The combined contribution limit applies to the total across both accounts.

Contribution Limits

The IRS sets annual contribution limits that are adjusted for inflation. For 2024, the limits are:

• Employee elective deferrals: $23,000 per year
• Catch-up contributions (age 50+): Additional $7,500, for a total of $30,500
• Total contributions (employee + employer): $69,000, or $76,500 with catch-up

Contributions are made through automatic payroll deductions, making consistent saving easier. Employees who do not actively enroll may be automatically enrolled at a default rate (commonly 3–6% of salary) under plans with auto-enrollment features required by the SECURE 2.0 Act for new plans established after 2024.

Employer Matching

One of the most valuable features of a 401(k) is the employer match — free money added to your account up to a specified limit. A common formula is a 100% match on contributions up to 3% of salary, plus a 50% match on the next 2%, effectively adding up to 4% of salary if the employee contributes at least 5%.

Failing to contribute enough to capture the full employer match is widely regarded by financial planners as leaving money on the table. The match immediately provides a 50–100% return before any investment growth.

Vesting Schedules

Employer matching contributions are not always immediately yours. Vesting schedules determine when you gain full ownership of employer contributions.

Employee contributions are always 100% vested immediately. If you leave a job before being fully vested, you forfeit unvested employer contributions.

Investment Options

Most 401(k) plans offer a curated menu of investment options, typically including:

• Target-date funds — automatically rebalance from stocks toward bonds as a target retirement year approaches
• Index funds — low-cost funds tracking market indexes like the S&P 500
• Actively managed mutual funds — professionally managed but generally carry higher fees
• Stable value or money market funds — lower risk, lower return options for capital preservation
• Company stock — available at some employers, though overconcentration carries risk

Investment returns inside a 401(k) compound without annual tax drag, which is a significant long-term advantage compared to taxable brokerage accounts.

Withdrawals and Penalties

Funds in a traditional 401(k) are intended for retirement and come with rules governing access:

• Qualified withdrawals: Available penalty-free at age 59½ and older; taxed as ordinary income
• Early withdrawals: A 10% penalty plus ordinary income tax applies before age 59½ (with limited exceptions for hardship, disability, or substantially equal periodic payments)
• Required Minimum Distributions (RMDs): Must begin at age 73 for traditional 401(k)s
• Loans: Many plans allow borrowing up to 50% of the vested balance or $50,000, whichever is less, repaid with interest back into your own account

Rolling Over a 401(k)

When leaving a job, participants typically have four options: leave the funds in the former employer's plan, roll over to the new employer's plan, roll over to an Individual Retirement Account (IRA), or cash out (which triggers taxes and potentially penalties). Rolling over to an IRA often provides broader investment choices and lower fees.

This article is for informational purposes only and does not constitute financial or investment advice. Consult a qualified financial advisor for guidance specific to your situation.