What Is a 401(k) and How Does It Work? A Complete Beginner's Guide

If your employer offers a 401(k) and you're not using it — especially if there's a match — you're leaving free money on the table. A 401(k) is the cornerstone of retirement savings for most Americans, yet many employees enroll without understanding what they've signed up for. Here's a plain-English breakdown.

What Is a 401(k)?

A 401(k) is an employer-sponsored retirement savings account that lets you invest a portion of each paycheck before taxes are taken out. The money grows tax-deferred — meaning you don't pay taxes on gains each year, only when you withdraw in retirement. This tax break allows your money to compound much faster than in a regular brokerage account.

2025 Contribution Limits

• Under 50: up to $23,500/year
• Age 50–59 or 63–64: up to $31,000/year (catch-up contribution)
• Age 60–63: up to $34,750/year (enhanced catch-up under SECURE 2.0)
• Employer contributions don't count toward your personal limit
• Total limit including employer: $70,000/year

The Employer Match: Never Leave It on the Table

Many employers match a portion of your contributions — commonly 50% or 100% of your contribution up to 3–6% of your salary. If you earn $60,000 and your employer matches 100% up to 4%, that's $2,400 in free money per year. Not contributing enough to get the full match is the most expensive financial mistake most employees make.

Traditional 401(k) vs Roth 401(k)

• Traditional 401(k): contributions are pre-tax, reducing your taxable income now; withdrawals in retirement are taxed
• Roth 401(k): contributions are after-tax (no immediate deduction); withdrawals in retirement are completely tax-free
• If your employer offers both, younger or lower-income workers generally benefit more from the Roth option
• Employer match always goes into the Traditional (pre-tax) bucket, regardless of your choice

What to Invest In

Most 401(k) plans offer a menu of mutual funds and target-date funds. For most people, a target-date fund (e.g., 'Target 2055 Fund' if retiring around 2055) is the simplest choice — it automatically adjusts allocation from aggressive growth to conservative as you near retirement. If you prefer more control, a simple three-fund portfolio (US stocks, international stocks, bonds) works well.

When Can You Withdraw?

• Age 59½: penalty-free withdrawals begin
• Age 73: Required Minimum Distributions (RMDs) must begin
• Early withdrawal (before 59½): 10% penalty plus income tax — avoid if at all possible
• Exceptions to the 10% penalty: disability, death, certain medical expenses, substantially equal periodic payments