What is the “look-back” period as defined by PPACA? In general, the look-back measurement method allows the employer to select a look-back period of time to measure whether the employee worked an average of 30 hours per week. If the employee worked an average of 30 hours per week during the look-back period, the employer must consider the employee a full-time employee during the subsequent “stability” period, regardless of the number of hours the employee works during the stability period. An employer may determine full-time status by using a look-back period of between three and 12 months.