Complete Guide to 401(k) Retirement Plans

A 401(k) is an employer-sponsored retirement savings plan that allows you to contribute a portion of your pre-tax salary directly from your paycheck. Contributions reduce your taxable income for the year — if you earn $80,000 and contribute $10,000, you are only taxed on $70,000. Your investments grow tax-deferred, meaning you pay no taxes on gains, dividends, or interest until you withdraw the money in retirement. Many employers offer matching contributions, essentially giving you free money for participating. For 2025, the maximum employee contribution is $23,500 for those under 50, with an additional $7,500 catch-up contribution allowed for those 50 and older, bringing the total to $31,000. The combined employer-and-employee contribution limit is $70,000 for 2025.

Employer matching is the single best return on investment available in personal finance. A common match formula is 50% of employee contributions up to 6% of salary. If you earn $80,000 and contribute 6% ($4,800), your employer adds $2,400 — an instant 50% return on your contribution before any investment gains. Some employers offer dollar-for-dollar matching, and a few match up to 10% or more of salary. Not contributing enough to receive the full employer match is literally leaving free money on the table. Even if you have other financial priorities like paying off debt, contributing at least enough to capture the full match should be your first priority. Employer contributions typically vest over time, meaning you may need to work for the company 3 to 6 years before the matched funds are fully yours.

Most 401(k) plans offer a menu of 15 to 30 investment options including stock funds, bond funds, and target-date funds. Target-date funds are designed for hands-off investors — you select the fund closest to your expected retirement year, and it automatically adjusts the stock-to-bond ratio as you age, becoming more conservative over time. If you prefer to build your own portfolio, a common guideline is to subtract your age from 110 to determine your stock allocation (a 30-year-old would hold 80% stocks, 20% bonds). Prioritize low-cost index funds when available, as even small fee differences compound significantly over decades. A fund charging 1% annually instead of 0.1% will cost you approximately $230,000 over a 40-year career on a $500,000 portfolio.

Many employers now offer a Roth 401(k) option alongside the traditional pre-tax 401(k). Traditional contributions reduce your taxable income now and are taxed upon withdrawal in retirement. Roth contributions are made with after-tax dollars — no immediate tax break — but withdrawals in retirement are completely tax-free, including all investment gains. The Roth option tends to be better for younger workers in lower tax brackets who expect to be in higher brackets in retirement. Traditional contributions tend to favor higher earners who are currently in peak tax brackets. You can split contributions between both types. Note that employer matching contributions always go into the traditional (pre-tax) side regardless of your election. Both types share the same annual contribution limit.

Withdrawals from a traditional 401(k) before age 59 1/2 generally incur a 10% early withdrawal penalty plus ordinary income taxes. Several exceptions apply: the Rule of 55 allows penalty-free withdrawals if you leave your employer during or after the year you turn 55. Substantially equal periodic payments (SEPP / Rule 72(t)) allow penalty-free withdrawals at any age if taken as a series of roughly equal annual distributions. Hardship withdrawals may be permitted for specific needs like preventing eviction or covering medical expenses, but they are still subject to taxes and penalties. Required minimum distributions (RMDs) begin at age 73 (starting in 2023, increasing to 75 in 2033). If you leave a job, you can roll your 401(k) into an IRA or your new employer's plan to maintain tax-deferred growth and potentially access better investment options.