Texas Labor Code - LAB § 408.041. Average Weekly Wage

(a) Except as otherwise provided by this subtitle, the average weekly wage of an employee who has worked for the employer for at least the 13 consecutive weeks immediately preceding an injury is computed by dividing the sum of the wages paid in the 13 consecutive weeks immediately preceding the date of the injury by 13.

(b) The average weekly wage of an employee whose wage at the time of injury has not been fixed or cannot be determined or who has worked for the employer for less than the 13 weeks immediately preceding the injury equals:

(c) If Subsection (a) or (b) cannot reasonably be applied because the employee's employment has been irregular or because the employee has lost time from work during the 13-week period immediately preceding the injury because of illness, weather, or another cause beyond the control of the employee, the commissioner may determine the employee's average weekly wage by any method that the commissioner considers fair, just, and reasonable to all parties and consistent with the methods established under this section.