How does a 401(k) work?

A 401(k) is an employer retirement plan that lets you contribute pre-tax pay, lowering your taxable income now. The money grows tax-deferred and is taxed as ordinary income when you withdraw it in retirement.

Should I contribute to my 401(k) if there is no match?

Often yes, because the tax deferral and automatic saving are valuable on their own. But compare the plan's fees and choices with an IRA, which may offer lower costs.

What is the 401(k) contribution limit?

The IRS sets an annual cap that rises most years, with an extra catch-up amount once you reach age 50. The 401(k) Calculator shows how the balance grows at your contribution level.

How a 401(k) Works: Contributions, Employer Match, and Growth

Key takeaway

Contribute at least enough to capture the full employer match, then let early, consistent contributions do the heavy lifting over time.

A 401(k) is a workplace investment account with tax perks

A 401(k) is a retirement account offered through an employer. You decide what percentage of your paycheck to contribute, the money is invested for the long term, and in exchange you get tax advantages you would not get in a regular brokerage account.

The "401(k)" name just refers to the section of the tax code that created it. What matters in practice is that it does three things at once: it automates saving straight from your paycheck, it lowers or defers your taxes, and it often comes with free money from your employer.

How contributions work

You choose a contribution rate, usually a percentage of your salary, and that amount is taken out of each paycheck before you ever see it. Because it happens automatically and before the money hits your checking account, a 401(k) sidesteps the biggest obstacle to saving: having to decide to do it every month.

With a traditional 401(k), contributions come out before income tax. That lowers your taxable income now, and you pay tax later when you withdraw in retirement. With a Roth 401(k), if your plan offers one, you contribute after-tax money and qualified withdrawals later are tax-free. Many people split the difference or choose based on whether they expect higher taxes now or in retirement.

There is an annual limit on how much you can contribute, set by the IRS and adjusted most years, with a higher limit for workers age 50 and over. You do not need to hit the maximum for the account to work, but the limit is a useful ceiling for pacing your contributions.

The employer match is the headline feature

Many employers match part of what you contribute. A common structure is a dollar-for-dollar match up to a few percent of your salary. For example, an employer might match 100% of your contributions up to 4% of pay.

There are very few guaranteed returns like it. If you earn $75,000 and your employer matches up to 4%, contributing at least 4% earns you an extra $3,000 a year you would otherwise leave on the table. Skipping the match is effectively turning down a guaranteed return on your own savings.

The practical rule that follows: if you can only do one thing with your retirement saving, contribute at least enough to capture the full match before anything else.

Why time matters more than the exact rate

A 401(k) is built for decades of compounding, and that long runway is what makes it powerful. Money contributed in your twenties and thirties has thirty or forty years to grow, so each early dollar does far more work than the same dollar added late in your career.

This is why raising your contribution rate even slightly when you are young can outweigh chasing a slightly higher investment return later. The largest single lever on your final balance is usually how early and how consistently you contribute, not the precise percentage your investments earn in any given year.

Vesting: when the match is truly yours

Your own contributions are always 100% yours. Employer contributions can be different. Some plans use a vesting schedule, meaning you have to stay with the company for a certain number of years before the matched money fully belongs to you.

If you are thinking about changing jobs, it is worth checking your vesting status. Leaving a few months before a vesting milestone can mean walking away from employer money you would otherwise keep. This does not mean you should stay in a bad job for a match, but it is a detail worth knowing before you give notice.

Common mistakes to avoid

Contributing below the match. This is the most expensive mistake, because it forfeits guaranteed employer money.
Leaving the default investment unexamined. Auto-enrollment often starts you at a low rate in a conservative default. Check both.
Cashing out when you change jobs. Rolling the balance into a new 401(k) or an IRA keeps it growing and avoids taxes and penalties.
Ignoring fees. Some plans have high-cost fund options. Lower-cost index funds, where available, keep more of the growth working for you.

How to think about the projected balance

When you project a 401(k) forward, you are stacking three things: your contributions, the employer match, and investment growth on top of both. The growth portion tends to dominate the final number over long horizons, which is the compounding effect doing its job.

A projection holds your salary, contribution rate, and return steady to keep the picture clear. Real life will include raises, market swings, and changing contribution limits. Use the estimate to test whether your current pace is in the right range, then revisit it whenever your pay or your match changes.

Use the 401(k) Calculator to project your balance including the employer match, the Roth IRA Calculator to compare a tax-free account alongside it, and the Retirement Calculator to see how everything adds up against your retirement timeline.