IRS requires employers to look at no less than 3 and no more than 12 calender months (chosen by the employer) to set average hours. "Scheduled" is not a factor

IRS requires employers to look at no less than 3 and no more than 12 calender months (chosen by the employer) to set average hours. "Scheduled" is not a factor in the law, it is how many hours the employee works on average over the "lookback" period