Employer-Sponsored Retirement Plans: Age, Service, and Entry Rules

The minimum service requirements for employer-sponsored retirement plans are set by federal law: a qualified plan generally cannot make you wait longer than one year of service and age 21 to participate. Whichever comes later is when you become eligible. A plan can be more generous, and many are, but it cannot demand more than that ceiling, with a couple of specific exceptions and a separate pathway for long-term part-time workers.

The One-Year, Age 21 Ceiling

A qualified retirement plan cannot require more than one year of service or attainment of age 21 before you participate.¹ Eligibility hinges on the later of the two milestones. Finish your first year before turning 21? You wait until your 21st birthday. Turn 21 before you complete a year of service? You wait until that year is up.

This ceiling shows up in both the Internal Revenue Code and ERISA, so it governs tax qualification and Department of Labor compliance alike.² Plans routinely go below it. Some 401(k)s let you contribute on your first day of work. The point of the federal rule is the maximum, not the norm.

What Counts as a Year of Service

A “year of service” is not just twelve months on the payroll. Under federal regulations, you complete a year of service when you log at least 1,000 hours during a designated twelve-month computation period.³ For a 40-hour week, that works out to roughly 25 weeks. Part-time workers can still hit 1,000 if their hours accumulate across the full year.

Hours of service include more than time on the clock. Any hour for which you are paid or entitled to payment counts, including vacation, sick leave, holidays, and back-pay awards.

Your first computation period starts on your date of hire and runs twelve consecutive months. If you fall short of 1,000 hours in that window, the plan shifts to a second computation period. Many plans align that second window with the plan year; others use your hire anniversary. The plan document picks the method.

The Elapsed Time Alternative

Some plans skip hour tracking entirely and use the elapsed time method. Service runs from your hire date to your departure date, and a year of service means twelve months of continuous employment.⁴ It’s simpler to administer and common for salaried roles where precise hours are hard to capture. Whichever method a plan picks, it must apply it uniformly to employees in the same classification.

The Two-Year Exception With Immediate Vesting

There is one narrow way for a plan to require more than a year of service. A plan may demand up to two years, but only if you are 100% vested in all employer contributions the moment you enter.¹ Graded vesting is not allowed under this arrangement.

For 401(k) plans, the two-year rule reaches only employer contributions. Your own elective deferrals must be available after no more than one year of service, even when the plan uses a two-year rule for the employer side.⁵

The 500-Hour Pathway for Long-Term Part-Time Workers

Before 2024, a part-time employee who never crossed 1,000 hours in a single year could be shut out of a 401(k) indefinitely. The SECURE Act and SECURE 2.0 opened a separate door. Work at least 500 hours in each of two consecutive twelve-month periods, and the plan must let you make elective deferrals.⁶ You still need to be at least 21 by the end of the second period.

The original SECURE Act required three consecutive years. SECURE 2.0 cut that to two, effective for plan years beginning after December 31, 2024.⁷ Twelve-month periods before January 1, 2021 don’t count toward the total.⁸

The pathway covers 401(k) elective deferrals and, for plan years after December 31, 2024, ERISA-covered 403(b) plans.⁷ It does not entitle you to employer contributions. Plans covering collectively bargained employees or nonresident aliens with no U.S.-source income may exclude those groups from the long-term part-time rules.⁸

When You Actually Enter the Plan

Meeting the age and service thresholds doesn’t put you in the plan the same day. Federal law gives the plan a short grace window, but caps it. You must be admitted by the earlier of:

the first day of the next plan year after you satisfied the requirements, or
six months after the date you satisfied them.

Whichever falls first is the deadline.¹ The maximum gap between qualifying and entering is six months. The same entry-date rules apply to long-term part-time workers who qualify through the 500-hour pathway.⁸

Rehires and Breaks in Service

If you leave a job and come back, whether your earlier service still counts depends on breaks in service. A one-year break in service occurs when you complete 500 or fewer hours during a computation period.⁹ You don’t have to quit to trigger one; reduced hours alone can do it if you drop below the threshold.

When you return, the plan measures eligibility from your reemployment commencement date using a fresh twelve-month computation period. If you already completed enough service before leaving, the plan may be required to credit that prior service. The specifics depend on the plan’s rules and how many consecutive breaks you accumulated.

Service Across Related Employers

If your employer belongs to a controlled group or an affiliated service group, service with any member of that group counts toward eligibility in a plan maintained by another member. Federal law treats all employees across the group as employed by a single employer for participation, vesting, and contribution testing.¹⁰ Transferring from one entity to a sister entity should not restart your eligibility clock. Employees don’t always know their employer is part of such a group, and administrators sometimes miss cross-entity service when records don’t flag it.

Employees a Plan May Still Exclude

The age-and-service ceiling is a floor for coverage, not a guarantee. Certain groups can be excluded without violating federal law even after they meet the thresholds:

Employees covered by a collective bargaining agreement can be excluded from a non-union plan, provided retirement benefits were actually part of the bargaining.¹¹
Nonresident aliens who receive no U.S.-source earned income from the employer are treated as excludable.¹¹

These exclusions are optional; a plan can cover either group if it chooses. It must still pass nondiscrimination testing among the employees it does cover.

SIMPLE IRA and 403(b) Plans Work Differently

The one-year, 1,000-hour framework is the standard, but two common plan types run on their own rules.

SIMPLE IRAs

SIMPLE IRAs, aimed at small employers, use a compensation test instead of hour counting. The employer must allow participation by any employee who earned at least $5,000 in any two preceding calendar years and is reasonably expected to earn at least $5,000 in the current year.¹² There is no age 21 requirement and no 1,000-hour test. The employer can set a lower compensation threshold but cannot add service or age conditions.

For taxable years after December 31, 2024, the $5,000 figure is indexed for inflation and rounded to the nearest $100.¹² Check the current IRS cost-of-living adjustment for the applicable year.

403(b) Plans

A 403(b), available to public schools, universities, and nonprofits, is governed by a universal availability rule. If a 403(b) allows any employee to make elective deferrals, it generally must extend that opportunity to all employees of the organization.¹³ A plan can exclude specific groups, including employees already eligible under a 401(k) or 457(b) of the same employer, nonresident aliens, and students performing services under the FICA student exception.

For employer contributions to an ERISA-covered 403(b), the standard age 21 and one-year service rules apply. Governmental 403(b) plans and church plans that haven’t elected ERISA coverage have more latitude, with their eligibility terms set by the plan document rather than the federal minimums.

1
Office of the Law Revision Counsel. 26 USC 410 – Minimum Participation Standards
2
Office of the Law Revision Counsel. 29 US Code 1052 – Minimum Participation Standards
3
eCFR. 29 CFR 2530.200b-1 – Computation Periods
4
eCFR. 26 CFR 1.410(a)-7 – Elapsed Time
5
Internal Revenue Service. 401(k) Plan Qualification Requirements
6
Office of the Law Revision Counsel. 26 USC 401 – Qualified Pension, Profit-Sharing, and Stock Bonus Plans
7
Internal Revenue Service. Additional Guidance with Respect to Long-Term, Part-Time Employees
8
Federal Register. Long-Term, Part-Time Employee Rules for Cash or Deferred Arrangements Under Section 401(k)
9
eCFR. 29 CFR 2530.200b-4 – One-Year Break in Service
10
Internal Revenue Service. Controlled and Affiliated Service Groups
11
eCFR. 26 CFR 1.410(b)-6 – Excludable Employees
12
Office of the Law Revision Counsel. 26 USC 408 – Individual Retirement Accounts
13
eCFR. 26 CFR 1.403(b)-5 – Nondiscrimination Rules