How Your 401(k) Works, and the Decisions You Control

• How much you contribute

  Often the plan, at first

  If you were enrolled automatically, your plan selected the initial contribution rate. Review the plan's matching formula and determine whether your current contribution qualifies for the full available match.

• Pre-tax or Roth

  Yours, if the plan offers both

  Many plans allow contributions to be divided between pre-tax and Roth accounts. Pre-tax contributions may lower taxable income today, while qualified Roth withdrawals are tax-free. The appropriate mix depends partly on your current and expected future tax situation.

• How the money is invested

  The default, unless you change it

  Your investment selection can materially affect the long-term outcome. If your money entered a default investment automatically, review its allocation, costs, and risk level to determine whether it fits your time horizon and circumstances.

• What happens when you leave

  Yours, and easy to overlook

  When you leave a job, you generally have four options for the account. Vesting may also matter: your contributions are always yours, while employer contributions may be subject to the plan's vesting schedule.

01

What is a 401(k)?

A 401(k) is a retirement savings plan offered through an employer, named for the section of the tax code that created it. It is a defined-contribution plan, not a pension: what you end up with depends on what goes in and how it is invested, not on a promised monthly payout. You contribute a portion of your paycheck, the investments receive tax-advantaged treatment while the money stays in the plan, and many employers add money of their own.

02

How money goes in

Contributions come out of your paycheck automatically as elective deferrals, before the money reaches your bank account. Many plans now enroll new employees automatically and raise the deferral rate a little each year unless you opt out. One thing that is easy to miss: the default rate may or may not qualify for the full employer match, so it is worth confirming your own rate rather than leaving it on the default.

03

How the employer match works

Where a plan offers a match, the employer adds money based on what you contribute, up to a cap. Common formulas are a partial match (a set share of your contribution) or dollar-for-dollar, up to a percentage of your pay. Because the match is effectively additional compensation, contributing at least enough to receive the full match is a common consideration. The exact formula is set by your plan, so the plan documents are the place to confirm it.

04

Vesting and what happens to the match

Your own contributions are always 100% yours. The employer match, though, may vest over time: some plans vest it immediately, while others use a cliff schedule (fully vested after a set number of years) or a graded schedule (vesting a percentage each year). If you leave before you are fully vested, you can forfeit the unvested part of the match. That is why the vesting schedule in your plan documents is worth understanding before timing a departure.

05

Pre-tax (traditional) vs Roth 401(k)

The main difference is when the money is taxed. Pre-tax (traditional) contributions can lower your taxable income now and are taxed when you withdraw in retirement; Roth contributions are made with after-tax dollars, and qualified withdrawals are tax-free. Unlike a Roth IRA, a Roth 401(k) has no income limit. Two details people miss: an employer match generally lands in a pre-tax account even when you contribute Roth, unless the plan has adopted a Roth match, and a Roth 401(k) has its own five-year clock for tax-free withdrawals. A common consideration is whether you expect a higher or lower tax rate later. This is general information, not tax advice.

06

Contribution types and the two separate limits

There are actually two limits, which people often blur together. The first caps what you can defer from your own paycheck each year, with an additional catch-up amount once you reach age 50 and a larger one in your early 60s. The second, higher limit caps the total of all contributions to your account - yours, the employer's, and any after-tax contributions combined - so employer money rides on top of your deferral limit rather than eating into it. Some plans also allow after-tax (non-Roth) contributions above the deferral cap, and higher earners are now required to make their catch-up contributions as Roth, a rule effective in 2026. All of these figures change most years; see IRS.gov for the current amounts.

07

Loans from your 401(k)

If your plan permits it, you may be able to borrow from your own balance and repay the plan account, with interest, over time. A loan is not taxed as long as you repay it on schedule. But if you leave the job or default, the outstanding balance can be treated as a distribution - taxable, and potentially subject to an additional 10% federal tax if you are under 59½ and no exception applies. There is also an opportunity cost, since the borrowed amount is no longer invested while the loan is outstanding. See IRS.gov.

08

Hardship and in-service withdrawals

Some plans allow withdrawals while you are still employed. A hardship distribution is limited to an immediate and heavy financial need and to the amount necessary to meet it; unlike a loan, hardship money is generally taxed and cannot be repaid or rolled over. Separately, many plans allow in-service withdrawals at age 59½, and newer rules permit a small annual emergency withdrawal. What your plan allows varies, so confirm the specifics before counting on access. See IRS.gov.

09

The cost of withdrawing early

Money taken out before age 59½ is generally subject to ordinary income tax plus an additional 10% early-withdrawal tax, though exceptions exist. For example, separating from an employer in or after the year you turn 55 can allow withdrawals from that employer's plan without the additional 10% federal tax. An early withdrawal also may reduce the amount remaining for future tax-advantaged growth. See IRS.gov for the current exceptions.

10

Required minimum distributions

Eventually the IRS requires you to start taking money out. Required minimum distributions (RMDs) begin at a set age, which recent legislation has been raising over time, and missing one carries an excise tax. Roth 401(k) balances are no longer subject to lifetime required distributions for the original owner. See IRS.gov for the current RMD age and rules.

11

What happens to your 401(k) when you leave a job?

When you leave a job, your old 401(k) does not have to stay where it is. You generally have four options: leave it in the former plan, move it to a new employer's plan, roll it into an IRA, or cash out. Each has tradeoffs, and withdrawals before age 59½ may be subject to income tax and an additional 10% federal tax, with some exceptions. Our rollover guide walks through the options without recommending one. This is general education, not tax or legal advice; for specifics, see the IRS or a qualified professional.

• IRS - 401(k) PlansThe canonical government overview of how a 401(k) is set up, run, and used.
• IRS - 401(k) Contribution LimitsThe current-year deferral cap, catch-up amounts, and the overall annual-additions limit.
• IRS - Roth Comparison ChartSide-by-side of Roth 401(k), Roth IRA, and pre-tax 401(k): taxation, limits, and withdrawals.
• IRS - Hardships, Early Withdrawals, and LoansWhich plans may offer loans, and the tax on withdrawals taken before age 59½.
• IRS - Hardship DistributionsThe immediate-and-heavy-need test and why hardship money cannot be rolled over.
• SEC (Investor.gov) - 401(k) PlansThe SEC investor-education glossary entry on workplace 401(k) plans.

Last updated September 2026. General education, not financial, tax, or legal advice. Parsonex does not recommend a particular course of action on this page.