Many employers still struggle with the Affordable Care Act’s look-back rules, and understandably so. But these rules matter because they help determine which employees must be offered health coverage to avoid potential employer shared responsibility penalties under IRC Section 4980H(a).

For employees with steady hours, the answer is often simple. For employees whose hours fluctuate, employers typically use the ACA’s look-back measurement method to determine whether they averaged enough hours to be treated as full-time. In general, the process involves three periods:

1. Measurement Period: Hours are tracked over a defined period.
2. Administrative Period: Time to determine eligibility and process enrollment.
3. Stability Period: The employee’s status is locked in, regardless of actual hours worked.

What Is a Variable Hour Employee?

A variable-hour employee is not simply paid hourly. Under the ACA rules, a new hire is a variable-hour employee if, based on the facts at the start date, the employer cannot reasonably determine whether the employee is expected to average at least 30 hours of service per week during the initial measurement period because the employee’s hours are uncertain or variable.

This differs from employees whose status is clear at hire:

• Full-time employees are reasonably expected to average 30 or more hours of service per week
• Part-time employees are reasonably expected to average fewer than 30 hours of service per week

Variable-hour employees fall somewhere in the middle because the employer cannot reasonably determine whether the employee is expected to average at least 30 hours per week.

How Long Can These Periods Be?

For ongoing employees, the standard measurement period can be between 3 and 12 months. If an employee measures as full-time, the stability period must be at least 6 consecutive months and cannot be shorter than the measurement period. An administrative period may be used between those periods, but it cannot effectively shorten or extend the measurement or stability period, and generally cannot exceed 90 days.

For new variable-time employees, the initial measurement period is also between 3 and 12 months. Employers may then use an administrative period, but the combined initial measurement period and administrative period generally cannot extend beyond the last day of the first calendar month beginning on or after the employee’s first anniversary date—often described as a maximum of 13 months plus a partial month.

What Happens When the Measurement Period is Less Than 6 Months?

For ongoing employees who do not measure as full-time, the follow-up stability period cannot exceed the measurement period. For new variable-time employees who are not measured as full-time, the stability period generally cannot exceed 1 month beyond the initial measurement period and is also capped by the remainder of the first full standard measurement period, plus any administrative period.

Why a 3-Month Measurement Period and 12-Month Stability Period Is Usually a Problem

A common mistake employers make is using a 3-month measurement period and then applying a 12-month stability period to employees who are not full-time.

Under ACA rules, the stability period for employees who do not measure as full-time generally cannot be longer than the measurement period. As a result, a 3-month measurement period will typically support no more than a 3-month non-full-time stability period.

While short measurement periods can work, they come with important limitations that employers should understand before implementing them.

Practical Tips for Employers

1. Review your plan design: Ongoing employees and new variable-hour employees are not always treated the same, and employees who measure as full-time are treated differently from those who do not.
2. Be cautious with short measurement periods: While a 3-month period may seem easier to administer, it often creates compliance issues when the employer also wants a longer stability period for non-full-time employees. Many employers find that longer, more balanced periods are easier to administer and defend.
3. Document variable-hour classifications: If a new hire was actually expected to be full-time, classifying them as variable-hour may create ACA exposure later. Consistent hiring and classification practices are essential to avoid mistakes.

The Bottom Line

ACA measurement period rules are manageable, but they need to be designed carefully. A quick check of your current approaches, especially if you are using a short measurement period and a long stability period, can help prevent costly errors later.