401(k)

Reviewed 12 August 2026 · Sourced from the Internal Revenue Code, the IRS and the U.S. Department of Labor

What a 401(k) actually is

The folder lands on your desk in the first week. A percentage box, a list of fund names that mean nothing to you, and a deadline. Nobody explains it, and the safe-feeling move is to leave the default alone.

So, before you fill in that box: a 401(k) is not an investment. It is a container — a place your pay can go instead of your checking account. The name is not a brand but a subsection number, 26 U.S.C. § 401(k), which the statute calls a qualified cash or deferred arrangement. You defer cash you would otherwise be handed.

It arrived in the Revenue Act of 1978, Pub. L. 95-600, at section 135, headed “Certain Cash or Deferred Arrangements,” printed at 92 Stat. 2785 and effective for plan years beginning after December 31, 1979.

The effective-date language carries what the popular story leaves out: the Act includes a transitional rule for arrangements that already existed on June 27, 1974. Congress was not designing a retirement plan for ordinary workers — it was writing rules for deferral arrangements companies already used, mostly for well-paid people.

You will read almost everywhere that a benefits consultant named Ted Benna invented the modern 401(k) around 1980 by reading the subsection creatively. We could not confirm it from a primary source, so it sits in the ledger as unverified.

What goes inside the bucket decides what you end up with. If the plan’s menu includes a low-cost index fund, you have the ingredient Stage 4 is built around.

The 2026 limits, and which ones will ever touch you

These reset every year for inflation. The 2026 figures come from IRS Notice 2025-67 and the IRS cost-of-living table. Anything still saying $23,500 is a 2025 page.

Add them for the real ceilings — our arithmetic, not a published figure. $24,500 plus $8,000 is $32,500 at 50 to 59 or 64 and up. $24,500 plus $11,250 is $35,750 in the narrow window from the year you turn 60 through the year you turn 63. That tier comes from section 109 of the SECURE 2.0 Act, and Notice 2025-67 says it “remains $11,250” — it did not rise this year, even though the ordinary catch-up did.

Now the honest part. If you are enrolling for the first time, or you are 45 with nothing saved, none of that is your constraint. $24,500 on a $50,000 salary is 49% of gross pay — $942.31 out of each of 26 paychecks, our division and not an IRS figure.

The other two quietly bite: the § 415(c) cap of $72,000 counts everything — your money, the match, profit sharing, forfeitures — and the § 401(a)(17) cap is why a percentage-of-pay match stops growing above $360,000 of salary.

The match, and the money that is not yours yet

Start with what surprises people: no law requires your employer to match a cent. The tax code governs matches if an employer makes them; it never orders one. That is why the formula lives in your plan document, and why two jobs across the street can offer wildly different deals.

A common shape is “100% of the first 3%, then 50% of the next 2%.” In dollars:

That $760 is why “at least get the full match” is repeated so often. No agency publishes it; it is arithmetic about an immediate 50% to 100% return available nowhere else — and it assumes you can afford the deduction, a real assumption when your emergency fund is empty.

Vesting: whose money is it

Your own contributions are 100% yours from the first paycheck; 26 U.S.C. § 411(a)(1) makes benefits from an employee’s own contributions nonforfeitable. The employer’s money is different. Section 411(a)(2)(B) lets a plan hold it on one of two schedules.

Ask HR for your vesting schedule and your years of service. That answer can be worth more than a raise.

Traditional or Roth, and the 2026 catch-up rule most articles get wrong

Most plans offer two flavors of the same account. Traditional contributions come out before income tax, so this year’s taxable income drops by what you put in, and everything you withdraw later is ordinary income. Designated Roth contributions are taxed now, and a qualified distribution later comes out tax-free, growth included.

The trade is easy to state and impossible to settle: you are guessing whether your tax rate is lower now or later. Someone earning $38,000 in a year they were also unemployed for two months is in an unusually low bracket; someone at their career peak has the opposite argument. One traditional-side effect worth naming: lowering your taxable income can pull you into range for the Saver’s Credit, which for 2026 phases out at $40,250 for single filers, $60,375 for head of household and $80,500 for joint filers, per Notice 2025-67.

The mandatory Roth catch-up for high earners

Section 603 of the SECURE 2.0 Act says certain higher-paid people can no longer make catch-up contributions pretax — their catch-up must be Roth. The year labels in the IRS notice are genuinely confusing, so take them one at a time.

For 2026, the trigger is more than $150,000 of FICA wages in 2025 from the employer sponsoring the plan. The threshold is named for the year of the wages, not the year of the contribution, which is what makes it easy to quote a year out of step. Notice 2025-67 settles it in one sentence: the wage threshold “for 2025, which under section 414(v)(7)(A) is used to determine whether an individual’s catch-up contributions to an applicable employer plan … for 2026 must be designated as Roth contributions, is increased from $145,000 to $150,000.” So $145,000 governed 2025 catch-ups, and $150,000 governs 2026.

Four details decide whether it touches you at all:

• The measure is FICA wages under § 3121(a) — Box 3 of your W-2. Not Medicare wages in Box 5, not gross comp, not household income.
• It is measured per employer. Start a new job and you had no prior-year FICA wages there, so it does not reach you.
• Someone with no FICA wages from the sponsor — a partner with only self-employment income, say — is outside it.
• If a plan has no Roth feature, affected high earners simply cannot make catch-up contributions.

Our source for the 2025-wage reading is a law firm’s analysis of the final regulations, not the regulations themselves. That distinction is in the ledger.

Getting money out early, and what it costs

The tax break has a fence around it. Take money from a traditional 401(k) before age 59½ and you generally owe ordinary income tax plus a 10% additional tax under § 72(t), per IRS Tax Topic 558.

The rule of 55, which an IRA does not have

Tax Topic 558 lists an exception for “distributions made to you after you separated from service with your employer after attainment of age 55.” It covers workplace plans — 401(k), 403(a), 403(b) — and the IRS is explicit that it does not apply to IRAs. Public safety employees get it at 50, or after 25 years of service.

Roll an old 401(k) into an IRA in your fifties and that protection is gone. What happens to the money later is covered in the withdrawal guide, and eventually by the required minimum distribution rules.

Hardship distributions

The IRS is clear that a plan “may” allow hardship distributions — it is not required to. Where offered, the safe-harbor list of immediate and heavy needs covers medical expenses, buying a principal residence, twelve months of tuition and room and board, preventing eviction or foreclosure, funeral expenses, and repairing damage to your home.

Loans

A plan may also let you borrow. Under § 72(p) the ceiling is 50% of your vested balance or $50,000, whichever is less, with an exception allowing up to $10,000 if your vested balance is under $20,000. Repayment is generally five years, with payments at least quarterly.

Loans feel harmless because you pay the interest to your own account — until you lose the job. The IRS notes the sponsor may demand repayment on termination; if you cannot pay, the balance is treated as a distribution and reported on Form 1099-R — taxable, and penalized under 59½. One escape hatch: roll an amount equal to the offset into an IRA or eligible plan by the due date of that year’s return, including extensions. Almost nobody just laid off has the cash.

The legally required document nobody opens

Somewhere in your email is a participant fee disclosure, required by the Department of Labor regulation at 29 CFR 2550.404a-5. It is not marketing — it is a legal obligation your plan owes you, and one of the few financial documents genuinely designed to be compared.

Per the Department of Labor’s A Look at 401(k) Plan Fees, you get investment information before you first direct investments and annually after: performance over one, five and ten years, a benchmark for each fund, and fees in a comparable format. Your quarterly statement separately shows fees actually paid from your account. DOL groups the costs three ways: plan administration fees (recordkeeping, legal, trustee), investment fees — the largest component, charged as a percentage of assets rather than billed to you — and individual service fees for optional things like a loan.

Two caveats, because that example gets quoted as a full-career projection: it assumes you never contribute another dollar, and 7% is an assumption. What survives both is the shape of it — a fee is a percentage of everything you have, charged every year, compounding against you the way growth compounds for you (see compound interest). So open the disclosure and find the expense ratio column.

Where a 401(k) sits next to everything else

The popular ordering — match first, then high-interest debt, then a Roth IRA, then back to the 401(k) — is a convention. A reasonable one, published by no agency. Treat it as a frame, not an instruction.

What separates them: a 401(k) is tied to a job, while a Roth IRA is yours with no employer and no match. The 401(k) limit is far larger, $24,500 against $7,500 in 2026. The 401(k) has the rule of 55 and the IRA does not. And the IRA has an open investment menu, while the 401(k) has whatever your plan bought — which is why the fee disclosure matters more here.

If you are 45 with nothing saved

The compounding stories are written for 25-year-olds, so here is arithmetic for the real case. All of it is our own calculation at an assumed 7% annual return compounded monthly — not a forecast, and real returns arrive in a jagged order that matters (see the withdrawal guide).

Two decades is still two decades, and the match is the only part of that equation which is not a market assumption. Starting late works through the rest, and Stage 5 picks up when the balance grows large enough to have its own problems.

What is confirmed, what is unverified, what is convention

What trips people up

1. Leaving the auto-enrollment default alone. Many plans enroll you automatically at a low percentage that sits below the full match tier. In our $38,000 example, 2% instead of 5% costs $760 of employer money a year — $3,800 over five years, before any growth.

2. Quitting one month before the cliff. Under a three-year cliff, two years and eleven months of service vests you at zero, forfeiting $4,560 of match contributions in our example. If you are within a year of a cliff, that number belongs in any job comparison.

3. Cashing out a small balance at a job change. An $8,000 balance feels like found money on your last day. At an assumed 22% bracket it is $1,760 of income tax plus $800 of additional tax, leaving $5,440. Left alone for 25 years at an assumed 7% it would be roughly $43,000 — our arithmetic, not a forecast.

4. Rolling everything into an IRA at 56. It looks like tidy consolidation. It also permanently deletes the rule of 55 for that money, because the IRS applies the exception to workplace plans and not to IRAs.

5. Taking a plan loan while the job feels shaky. A loan is not taxable while it is a loan. Lose the job and fail to repay, and it becomes a reported distribution — taxed and penalized in a year you have no income.

6. Never opening the fee disclosure. It is required by law and holds the one column, expense ratios, that quietly drives your outcome.

The figures on this page are checked against the source that publishes them, and dated. Published rates move after the release named above — the linked source always carries the current number. This page explains a term; it does not recommend a product.