401(k) Eligibility and Participation
The plan document defines who enters and when, within federal participation limits. Administration fails when hire dates, age, hours, elapsed time, employee classifications, entry dates, and payroll activation do not follow the same rule.
Reviewed July 29, 2026 · Source-led practitioner reference
Core eligibility framework
A qualified plan generally cannot require an employee to be older than 21 or complete more than one year of service to participate. A year of service commonly means at least 1,000 hours in a 12-month computation period. Special rules can support a two-year service condition for certain employer contributions if participants are fully vested after no more than two years.
Long-term, part-time employees
For plan years beginning in 2025 and later, SECURE 2.0 generally reduced the long-term, part-time threshold for 401(k) elective-deferral eligibility from three consecutive years to two consecutive 12-month periods with at least 500 hours, subject to age and other statutory rules. These employees may be excluded from employer contributions and certain testing when the governing requirements are met, but the plan and administrator must track the population correctly.
Eligibility is not the entry date
| Term | Control question |
|---|---|
| Eligibility conditions | Has the employee met age, service, and classification requirements? |
| Entry date | On what plan-specified date does participation begin after eligibility is satisfied? |
| Enrollment | Is enrollment affirmative, automatic, or subject to an opt-out process? |
| Contribution eligibility | Do deferrals, match, and nonelective contributions use the same population? |
Operational control
- Translate the signed plan document into testable system rules.
- Track excluded classes and related employers without relying on job labels alone.
- Preserve hours and elapsed-time history through transfers, rehires, and acquisitions.
- Audit eligible-but-not-enrolled employees before every entry date.
- Correct missed deferral opportunities and related contributions under current correction rules.
Turn reference knowledge into working confidence.
Use this public guide for quick orientation and source review. Inside PrepToPay Benefits, you can study the topic in structured lessons, practice applying it, review flashcards, and track your progress across the broader Benefits curriculum.
Primary sources
- IRS — 401(k) plan qualification requirements
- IRS Notice 2024-73 — long-term, part-time employees
- IRS — Plan disclosure documents and participation
Educational reference only. Plan documents, governing law, agency guidance, and plan-specific professional advice control.
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