Definition
A 401(k) plan is a defined contribution plan established under Internal Revenue Code Section 401(k) that permits an employee to elect to have a portion of compensation contributed to the plan on a pre-tax or Roth basis, with employer contributions optional.
Why it matters
The 401(k) plan is the dominant private-sector retirement plan form in the United States and the plan type through which most private-sector workers accumulate retirement savings. Its statutory structure defines how contributions, distributions, employer matching, and testing operate for the majority of the working-age population.
How it works
A 401(k) plan operates as a defined contribution plan with the specific feature that participants may elect to defer a portion of their compensation into the plan through payroll withholding, either as pre-tax contributions (excluded from current gross income and taxed at distribution) or as designated Roth contributions (included in current gross income and generally tax-free at distribution). Employers may match participant deferrals, make nonelective contributions, or both, subject to the plan's terms. For 2026, participant elective deferrals are capped at $24,500, with a catch-up of $8,000 for participants age 50 or older and a SECURE 2.0 catch-up of $11,250 for participants age 60 through 63; the total limit on combined participant and employer contributions is $72,000 (source: IRS Notice 2025-67). Traditional 401(k) plans are subject to annual nondiscrimination testing to ensure elective deferrals and matching contributions are not disproportionately concentrated among highly compensated employees; safe harbor 401(k) designs bypass this testing by adopting prescribed employer contribution formulas. Distributions are generally restricted until separation from service, death, disability, plan termination, attainment of age 59½, or financial hardship.
In practice
If you participate in a 401(k) plan, the operative decisions are how much to defer, whether to elect pre-tax or Roth treatment, how to allocate contributions across the investment menu, and — at retirement or job change — how to handle the account balance. A common baseline is deferring at least enough to capture the full employer match, since the match is compensation the participant forfeits by deferring less. At retirement, the balance is available for distribution as a lump sum, systematic withdrawal, rollover to an IRA, or, where the plan permits, purchase of an in-plan lifetime income option. A professional advising on 401(k) decisions should be able to name the plan's specific features — matching formula, vesting schedule, investment menu, available distribution and rollover options, and any lifetime income features — rather than working from generalities about 401(k) plans as a category.
In the Longevity Standard Framework
The 401(k) plan is the primary structural context in which Longevity Standard work reaches the largest population — the private-sector working-age population accumulating retirement savings in the DC. Because the 401(k) delivers a balance rather than a lifetime income by default, the 401(k) participant approaching retirement is the individual for whom lifetime income education is most relevant and valuable.
Related terms
- Defined contribution plan
- 403(b) plan
- 457(b) plan
- Elective deferral
- Employer matching contribution
- Roth 401(k)
- Automatic enrollment
- In-plan lifetime income option