A 401(k) is an employer-sponsored plan where employees contribute pre-tax dollars and employers often match a portion, creating immediate returns. Employer matching is effectively free money and should be prioritized; most experts recommend contributing at least enough to capture the full employer match before other financial goals.
From your prerequisite work on retirement savings fundamentals, you know that tax-advantaged accounts let your money grow without being taxed year by year. A 401(k) is the most common employer-sponsored version of this idea. Each pay period, your employer automatically deducts your elected contribution — say, 6% of your salary — and deposits it directly into your 401(k) account before income taxes are calculated. Because the contribution comes out pre-tax, you pay less income tax today; the tax bill is deferred until you withdraw the money in retirement, when you're likely in a lower bracket.
The employer match is the feature that makes a 401(k) uniquely powerful compared to an IRA you open yourself. A typical match might be "50% of contributions up to 6% of salary" — meaning if you contribute 6%, your employer adds another 3%, giving you a 50% instant return on that portion before any market growth. Failing to contribute enough to capture the full match is equivalent to leaving part of your compensation on the table. This is why financial planning guidance consistently puts "contribute up to the full employer match" at the top of the priority order — ahead of paying down moderate-interest debt and ahead of contributions to other accounts.
Beyond the match, 401(k)s have annual contribution limits set by the IRS — in 2024, $23,000 for employees under 50, with an additional $7,500 catch-up contribution allowed for those 50 and older. Most plans offer a menu of mutual funds, typically index funds, target-date funds, and sometimes company stock. The investment decisions you make inside the 401(k) are separate from the tax benefit — the wrapper provides the tax advantage regardless of which funds you choose. Vesting schedules are another key feature: your own contributions are always yours immediately, but employer match contributions may vest over two to six years, meaning you only keep them if you stay long enough.
One variation worth knowing is the Roth 401(k), which some employers offer alongside the traditional version. Roth contributions are made with after-tax dollars — no deduction today, but qualified withdrawals in retirement are entirely tax-free, including growth. Choosing between traditional and Roth depends on whether you expect your tax rate now to be higher or lower than your tax rate in retirement. If you're early in your career with relatively low income, Roth often wins; if you're at peak earnings and getting a large deduction now is valuable, traditional often wins. Many people split contributions between both to hedge. The mechanics of the account are the same — the only difference is when taxes are paid.