401(k) eligibility sounds like the simplest rule in your plan document, and it produces more corrections than almost anything else. An employee is hired, someone eyeballs the start date, and the plan either lets them in too early or keeps them out too long. Either direction is an operational failure — the plan was not run according to its own terms — and the fix falls on the employer, not the employee.
This is a plan sponsor problem, not a payroll problem. Below is how eligibility and entry dates actually work, where employers get tripped up, and the controls that keep the two in sync.
Eligibility and entry date are two different decisions
Your plan document answers two separate questions, and confusing them is the root of most errors:
- Eligibility — has this person satisfied the plan’s age and service requirements, and are they in a class the plan covers?
- Entry date — on which of the plan’s specified dates does that now-eligible person actually enter and begin deferring?
Someone can be eligible in March and not enter until the next entry date the document names. Someone can hit an entry date and still not be eligible because they never met the service condition. The document controls both, and the document — not habit, not the prior recordkeeper’s spreadsheet — is the only authority.
Read these five fields in the adoption agreement
- The minimum age condition, and whether it applies to all contribution sources.
- The service condition, and whether it is measured by elapsed time or by hours of service.
- Whether deferrals, match and any nonelective contribution use the same conditions — frequently they do not.
- The entry date frequency (for example immediate, monthly, quarterly, or semiannual) and whether entry is the date on or the date following satisfaction.
- The excluded classes, defined precisely: which job categories, locations or entities are written out of coverage.
Where employers get tripped up
1. Different rules for different money types
Plans commonly let employees defer quickly while imposing a longer wait for the employer contribution. Payroll systems often store one eligibility date per employee. The result: someone gets a match they were not yet due, or misses one they had earned. Track eligibility per source, not per person.
2. Rehires treated as new hires
A returning employee who already satisfied the service condition usually does not start over. Plans contain specific rules for prior service and for reentry on rehire. Treating every rehire as a fresh hire is one of the most common improper exclusions we see, and it hides easily because the payroll record looks brand new.
3. Part-time, seasonal and variable-hour employees
If your plan measures service in hours, someone working irregular schedules may quietly cross the threshold in a year nobody was watching. Long-term part-time rules have also expanded access for employees who work consistently across multiple years. If you have never re-examined how part-time staff are tracked, assume this is an open exposure.
4. Class exclusions that do not match reality
The document may exclude “leased employees” or a named division. Then the business changes: a division is folded in, contractors are reclassified, or an acquisition adds a payroll group nobody mapped to the plan. The exclusion language stays frozen while the workforce moves. Reconcile the excluded classes to your current org chart at least annually.
5. Entry dates that drift from payroll
An employee becomes eligible, receives the enrollment materials late, and the first deferral lands a payroll cycle or two after the entry date the document names. That gap is a missed deferral opportunity, and correcting it typically means an employer-funded contribution. The calendar in your payroll system must be the same calendar as the plan document.
6. Nobody owns the notice
Eligibility triggers a communication duty. If your plan has automatic enrollment, the notice is what makes the default deduction lawful — see our guide to automatic enrollment notices. Even without automatic enrollment, an employee who is never told they are eligible cannot make an informed election, and that shows up in an audit as an improper exclusion.
The compliance consequences
Eligibility errors do not stay contained. They flow into:
- Coverage and nondiscrimination testing — the tested population is wrong, so the results are wrong.
- Form 5500 participant counts — miscounted participants can affect whether the plan is above the participant-count threshold that triggers an independent audit.
- Corrective contributions — a wrongly excluded employee is generally made whole by the employer, with earnings.
- Vesting service — service credited for eligibility often interacts with vesting records, so one bad date can propagate.
None of these are payroll line items. They are fiduciary and plan-operation issues that land on the plan sponsor.
A self-audit you can run this quarter
- Pull the adoption agreement and write the age, service, entry-date and exclusion rules on one page, per contribution source.
- Export every employee hired, rehired or reclassified in the last 24 months from payroll, with hire date, rehire date, job class and hours.
- Compute each person’s eligibility date and entry date from the document rules — not from what the system already stored.
- Compare your computed entry date to the first deferral date on the payroll register. Investigate every mismatch.
- Compare your eligible population to the recordkeeper’s participant list. Anyone eligible and missing is a potential improper exclusion; anyone enrolled early is an ineligible participant.
- Check that each newly eligible employee received the enrollment materials, and keep the proof.
- Document the review, the exceptions found, and how each was resolved.
If step 4 or step 5 produces mismatches, treat it the way you would treat any other operational failure: identify the affected employees, quantify the impact, correct it under the established correction programs, and fix the process that caused it. The same discipline applies to late deferral deposits and other timing errors.
Controls that prevent the next error
- Store eligibility dates per contribution source in payroll, and re-derive them from the document rather than carrying them over from a prior provider.
- Add a rehire flag that forces a manual eligibility review instead of defaulting to a new-hire date.
- Run an hours report for part-time and variable-hour staff on a fixed schedule, not only at year end.
- Re-map excluded classes whenever you acquire, restructure or open a location.
- Put every entry date on the plan’s compliance calendar with an owner’s name against it, and keep the documentation with your audit-readiness file.
- Reconcile payroll to the recordkeeper’s participant census monthly, not annually.
What you can and cannot delegate
A capable 3(16) plan administrator can own the operational work: applying the document’s eligibility rules, monitoring service, tracking entry dates, issuing notices, reconciling census data, and driving corrections when something breaks. That is precisely the layer where these errors live, and it is why the depth of a provider’s service matters — not all 3(16) providers are the same.
What you cannot delegate is the decision to select and monitor the parties doing the work, and the plan design choices themselves. Those stay with the sponsor.
Admin316 goes further than most: we accept the ERISA 402(a) named fiduciary appointment, which the majority of providers decline. That means responsibility for plan operation sits in writing with us, not quietly with your HR team — and eligibility administration is exactly the kind of day-to-day duty that responsibility covers. Learn more about why sponsors work with Admin316 or how we support 401(k) plans.
Start with your own data
If you cannot say today, from your own records, which employees became eligible in the last twelve months and whether each one entered on the right date, that is the finding. It is also fixable — usually in a single review cycle.
Schedule a call with Admin316 and we will walk your eligibility rules against your payroll data and show you exactly where the gaps are.
Want more? Browse the full 401(k) & ERISA resource library for every Admin316 guide on plan administration, fiduciary duties and compliance.
