What Is a 401(k) and How Does It Work?

A 401(k) is an employer-sponsored retirement savings plan named after the section of the U.S. tax code that created it. It's one of the most common ways American workers save for retirement.

How contributions work

Employees who participate choose a percentage of each paycheck to contribute to their 401(k) account, which is then invested in a menu of options the employer's plan offers -- often a mix of mutual funds, including target-date and index funds. The IRS sets annual limits on how much employees can contribute, and those limits are adjusted periodically for inflation.

Employer matching

• Many employers offer to match a portion of employee contributions, up to a certain percentage of salary.
• A common example structure is matching 50% or 100% of contributions up to a set percentage of pay, though exact formulas vary by employer.
• Financial advisors commonly suggest contributing at least enough to receive the full employer match, since it functions as additional compensation.

Traditional vs. Roth 401(k)

Many plans offer both traditional and Roth options. Traditional 401(k) contributions are typically made pre-tax, reducing taxable income now, with withdrawals taxed in retirement. Roth 401(k) contributions are made with after-tax dollars, with qualified withdrawals in retirement generally tax-free.

Withdrawal rules

401(k) funds are intended for retirement, and withdrawals before age 59½ generally trigger both income tax and an early withdrawal penalty, with some exceptions. Required minimum distributions generally must begin at a certain age set by federal law.

This article is for general educational purposes and is not personalized financial or tax advice.

Vesting schedules

While an employee's own contributions to a 401(k) are always fully theirs, employer matching contributions are sometimes subject to a vesting schedule -- a set period of employment required before those matched funds fully belong to the employee. Vesting schedules vary by employer and are typically outlined in plan documents.

What happens to a 401(k) when changing jobs

When leaving an employer, workers generally have several options for an existing 401(k): leave it with the former employer's plan if allowed, roll it over into a new employer's plan, roll it into an individual retirement account (IRA), or, in some cases, cash it out -- though cashing out before retirement age typically triggers taxes and penalties and is generally discouraged by financial advisors due to the lost long-term growth.

Automatic enrollment and contribution escalation

Many employers now use automatic enrollment, signing new employees up for a default contribution rate unless they actively opt out, a design intended to increase participation based on research showing that default options significantly influence savings behavior. Some plans also offer automatic contribution escalation, gradually increasing an employee's contribution percentage each year, often timed to coincide with annual raises.

Fees inside a 401(k) plan

401(k) plans typically involve several layers of fees, including administrative costs for running the plan and expense ratios charged by the individual investment funds offered within it. Because these fees reduce net investment returns over time, financial advisors generally recommend reviewing a plan's fee disclosure documents and, where multiple fund options are available, favoring lower-cost funds when they fit an investor's goals.

Catch-up contributions

Workers aged 50 and older are permitted to contribute more to their 401(k) than the standard annual limit, through what the IRS calls a catch-up contribution. This provision is designed to give people closer to retirement an extra opportunity to build savings, particularly those who may not have been able to contribute as much earlier in their careers. Catch-up contribution limits are set separately from the standard limit and are also periodically adjusted for inflation.

What happens to a 401(k) after death

401(k) accounts allow the holder to name one or more beneficiaries who inherit the account after the holder's death, generally outside of the probate process, which can make the transfer faster and simpler than assets that pass through a will. Rules governing how a beneficiary -- particularly a spouse versus a non-spouse -- can manage an inherited 401(k), including required withdrawal timelines, are governed by federal tax law and have changed in recent years, which is one reason estate-planning professionals recommend periodically reviewing beneficiary designations.