Part-time employees are eligible for a 401(k) under federal law once they meet one of two service tests. The traditional path requires 1,000 hours of work in a 12-month period. Since plan years beginning in 2025, a second path opens the plan to workers who put in at least 500 hours in each of two consecutive years. You also need to be at least 21. Your own employer’s plan may be more generous than these federal minimums, but it cannot be stricter.
The 1,000-Hour Path
The Employee Retirement Income Security Act sets the floor. A 401(k) plan cannot require you to be older than 21 or to complete more than one year of service before joining.1Office of the Law Revision Counsel. 29 U.S.C. 1052 – Minimum Participation Standards A “year of service” is any 12-month period in which you work at least 1,000 hours. The clock usually starts on your hire date.
If you don’t hit 1,000 hours in that first year, the plan can switch to measuring your hours by the plan year, which is often the calendar year.1Office of the Law Revision Counsel. 29 U.S.C. 1052 – Minimum Participation Standards A part-time worker averaging about 20 hours a week reaches 1,000 hours in roughly 50 weeks.
Meeting the requirement doesn’t put you in the plan the next day. Federal law lets the plan wait up to six months after you qualify, or until the first day of the next plan year, whichever comes first.2Office of the Law Revision Counsel. 26 U.S.C. 410 – Minimum Participation Standards So if you cross 1,000 hours in July and the plan year starts every January, your enrollment should happen no later than the following January 1.
The 500-Hour, Two-Year Path
Workers who never reach 1,000 hours in a year now have a second route in. The SECURE Act of 2019 created a category called long-term, part-time employees, and the SECURE 2.0 Act of 2022 shortened the qualifying period. For plan years beginning after December 31, 2024, you qualify by working at least 500 hours in each of two consecutive 12-month periods.3Office of the Law Revision Counsel. 26 U.S.C. 401 – Qualified Pension, Profit-Sharing, and Stock Bonus Plans You still need to be 21 by the end of the last qualifying period.
The same rule extends to 403(b) plans that are subject to ERISA, so long-term part-time staff at schools, hospitals, and nonprofits gained the same right to make salary deferrals beginning with plan years after December 31, 2024.4Internal Revenue Service. Notice 2024-73 – Additional Guidance on Long-Term, Part-Time Employees
What Eligibility Actually Gets You
Being eligible under the long-term part-time rules guarantees your right to contribute your own money to the plan. It does not guarantee an employer match. Employers are not required to provide matching or nonelective contributions to long-term part-time employees, even when other participants in the same plan receive them.5Federal Register. Long-Term, Part-Time Employee Rules for Cash or Deferred Arrangements Under Section 401(k) The one exception is a SIMPLE 401(k), which must give its required employer contributions to long-term part-time employees on the same terms as everyone else.
If you qualify through the standard 1,000-hour rule instead, employer contributions generally follow the plan’s normal terms for full participants. The plan document controls the specifics.
Vesting Credit for Part-Time Years
Vesting decides how much of any employer contribution you keep if you leave. Your own contributions are always yours immediately. Employer contributions usually vest over a schedule that can run three to six years, and each year of service you complete moves you further along it.
Under the standard rule, a year counts toward vesting only if you work 1,000 hours in it. SECURE 2.0 changed this for long-term part-time employees: any 12-month period in which you log at least 500 hours counts as a vesting year. Only periods beginning on or after January 1, 2023 are eligible.4Internal Revenue Service. Notice 2024-73 – Additional Guidance on Long-Term, Part-Time Employees Earlier service years do not count. A part-time worker hired in 2018, for example, starts accumulating LTPT vesting credit only from 2023 forward.
Automatic Enrollment at Newer Plans
If your employer set up its 401(k) or 403(b) after December 29, 2022, the plan is required to enroll you automatically once you become eligible, starting with plan years beginning after December 31, 2024.6Federal Register. Automatic Enrollment Requirements Under Section 414A The default contribution rate starts between 3 and 10 percent of pay and rises by one percentage point each year until it reaches at least 10 percent, capped at 15 percent. You can change the rate or opt out whenever you want.
Several categories of employer are exempt from the automatic-enrollment requirement:
- Plans established on or before December 29, 2022
- Employers who have never had more than 10 employees
- Businesses in existence for fewer than three years
- Government and church plans
- SIMPLE 401(k) plans
For a part-time worker, the practical consequence is that contributions may already be coming out of your paycheck once you cross the eligibility threshold. If you recently qualified at a newer employer, check a recent pay stub before assuming you have to sign up.
Who Can Still Be Excluded
Two groups of workers can be kept out of a 401(k) regardless of hours worked:2Office of the Law Revision Counsel. 26 U.S.C. 410 – Minimum Participation Standards
- Employees whose retirement benefits were the subject of good-faith collective bargaining between a union and the employer. These workers are typically covered by a separate union plan.
- Nonresident aliens with no U.S.-source income.
These exclusions are tied to legal status, not schedule. If either applies to you, the long-term part-time rules will not open the employer’s plan to you.
How to Find Your Plan’s Specific Rules
Federal law is a floor. Many employers set easier terms: some allow participation after a few months, and some on the first day of work, regardless of hours. The document that spells out your plan’s actual eligibility, waiting period, entry dates, and vesting schedule is the Summary Plan Description. Your plan administrator must furnish it within 90 days of your becoming a participant, and you can request a copy from HR at any time before that.7Office of the Law Revision Counsel. 29 U.S.C. 1024 – Filing With Secretary and Furnishing Information to Participants and Beneficiaries
If you think you meet the eligibility rules but haven’t been enrolled, the Summary Plan Description is where to start. It tells you exactly what the plan requires and gives you the basis for asking your administrator to enroll you.