What Is a 401(k)?

If you have started a job with a US employer, there is a good chance a stack of onboarding forms mentioned a 401(k). Many people tick a box, pick whatever is pre-selected and never look at it again. That is a shame, because a 401(k) is often one of the most useful money tools an ordinary worker gets. This guide explains what it is, how the moving parts fit together and which questions are worth asking before you sign anything.

A quick note before we start: this article is general information, not financial advice. Your plan documents and a qualified professional are the right sources for decisions about your own money.

The short definition

A 401(k) is a retirement savings account offered through an employer. The name comes from the section of the US tax code that created it. You choose a share of each paycheck to put in, your employer sends that money straight into the account, and it is invested in funds you select from a menu the plan provides. The money is meant to stay there until retirement, and the tax rules reward you for leaving it alone.

How the money gets in

Contributions come out of your pay automatically, which is the quiet strength of the whole system. You never see the money in your checking account, so you are less tempted to spend it. Most plans let you set a percentage of salary and change it later, usually through an online portal or the HR department.

The IRS sets a yearly ceiling on how much an employee can contribute, and it is adjusted from time to time. Older workers are often allowed an extra "catch-up" amount. Because those figures change, check the current numbers on the IRS website or in your plan's materials rather than relying on an old article.

The employer match

Many employers add money of their own when you contribute. A typical arrangement says something like "we match a portion of what you put in, up to a set share of your salary." The exact formula varies widely, and some employers offer no match at all. If yours does, contributing at least enough to collect the full match is often described as the first priority, because skipping it means leaving part of your pay package unclaimed.

Vesting

Your own contributions are always yours. The employer's contributions, however, may "vest" over time, meaning you only keep them fully after a certain period of service. If you leave before then, some of the matched money can be taken back. Your plan's summary description spells out the schedule.

Traditional versus Roth

Many plans now offer two flavours, and the difference is all about when you pay tax.

	Traditional 401(k)	Roth 401(k)
Money goes in	Before income tax, lowering this year's taxable pay	After income tax, so no break today
While invested	Grows without yearly tax on gains	Grows without yearly tax on gains
When you withdraw in retirement	Withdrawals are taxed as income	Qualified withdrawals are generally tax-free
Often considered by	People who expect a lower tax rate later	People who expect a similar or higher rate later

Nobody knows their future tax rate for certain, which is why some people split contributions between both types. This is a good topic to raise with a tax professional if you are unsure.

What the money is invested in

A 401(k) is a container, not an investment by itself. Inside it you choose from a list of funds: stock funds, bond funds, money market options and often "target date" funds that shift gradually from stocks toward bonds as a chosen retirement year approaches. If you never make a choice, your contributions usually land in a default option picked by the plan.

Two things are worth checking on that menu:

• Fees. Each fund charges an annual expense ratio, and the plan may add administrative costs. Small percentages compound over decades, so compare them.
• Diversification. Spreading money across many companies and asset types reduces the damage any single one can do. Putting a large share into your own employer's stock concentrates risk in one place.

Getting money out

The trade-off for the tax benefits is limited access. Taking money out before the retirement age set in the tax rules usually means paying income tax plus an additional penalty, although there are specific exceptions. Some plans allow loans or hardship withdrawals, but these can set your savings back and carry their own rules. Treat the account as long-term money and keep a separate cash cushion for emergencies.

When you change jobs

Leaving an employer does not mean losing your 401(k). Common options include:

1. Leaving the money in the old plan, if it allows that.
2. Rolling it into your new employer's plan.
3. Rolling it into an individual retirement account (IRA).
4. Cashing out, which normally triggers taxes and possibly penalties, and is usually the costliest choice.

A "direct rollover", where the money moves from one provider to another without passing through your hands, avoids several common paperwork traps.

Questions to ask your HR team

• Is there a match, and what is the exact formula?
• How long until employer contributions are fully vested?
• Is a Roth option available?
• What are the total fees on the default fund?
• When can I start contributing, and how do I change my percentage?

A 401(k) works best as one piece of a wider plan that includes a budget and an emergency fund; our guide to managing your finances covers those foundations. And because rising prices slowly eat into what savings can buy, it is worth reading what inflation is and why it matters to you alongside this one.