What Is a Break in Service for 401(k) Eligibility?
Leaving a job and returning to it later raises a question most rehired employees never think to ask: does the time already worked still count toward retirement plan eligibility, or does the clock start over from zero.
The short answer
A break in service is a gap in employment long enough that a 401(k) plan, under its own written rules, can disregard some or all of an employee’s prior service when figuring out eligibility or vesting. Plans commonly define the threshold as a full plan year — typically 12 consecutive months — during which the employee completed fewer than a set minimum number of hours of service, often 501. Whether a break actually erases prior credit depends on the specific plan document and how long the person was gone.
Why plans track this at all
Retirement plans reward tenure, so they need a consistent way to decide when someone’s employment history genuinely restarts versus when it simply paused. Without a break-in-service rule, an employer could face endless questions about short leaves, seasonal layoffs, or brief resignations followed by rehire. The rule gives the plan administrator an objective test: count the hours in the relevant period, compare them to the threshold, and apply the plan’s stated consequence.
The rule of parity
Many plans use what’s called a rule of parity to decide whether a break wipes out prior service for vesting purposes. Under this approach, if the number of consecutive one-year breaks equals or exceeds the years of service completed before the break, the earlier service can be disregarded entirely once the employee returns. A shorter break, or one where prior service outweighs the gap, is more likely to be bridged rather than erased. The exact mechanics differ by plan, since the rule of parity is a permitted design choice rather than a single fixed formula.
When a rehired employee must requalify
Someone rehired after a short gap often re-enters the plan quickly, sometimes immediately, because the break didn’t meet the plan’s threshold. Someone rehired after a longer gap may need to satisfy the plan’s eligibility requirements again, as if starting fresh, particularly if the break exceeded the parity limit described above. This is one of several practical wrinkles that show up whenever someone changes jobs and later returns, alongside questions like what happens to a 401(k) balance during the time away. Vesting credit for employer contributions follows its own version of the same logic, since vesting schedules are also built around years of measured service.
What to check after a rehire
- How the plan defines a year of service. Some count actual hours worked; others use elapsed time from the hire date, which changes how a break gets measured.
- Whether prior contributions are still on file. Even when eligibility restarts, money already contributed to a 401(k) account generally remains the employee’s, separate from the question of new eligibility.
- The vesting percentage carried over, if any. Rules of parity affect whether past vesting years still count toward full ownership of employer contributions.
The takeaway
A break in service is really just a plan’s way of measuring whether an employment gap was short enough to bridge or long enough to treat as a fresh start. The specifics — the hours threshold, the parity rule, what carries over — live in the plan document, so the details can differ meaningfully from one employer’s 401(k) to another’s, and depend on circumstances that change from one situation to the next.