Computing Regular Rate of Pay - Irregular Hours
The regular rate for an employee who works irregular hours but is paid a salary on a fixed monthly basis is computed by converting the wages into weekly figures. The regular rate is computed for each week by dividing the weekly wage by the hours actually worked in a week. Overtime must be paid each week without offsetting it from other weeks in which fewer than 40 hours were worked unless the employer is proceeding under the 207(k) exemption for public safety officers or the 207(j) provision for hospitals and nursing homes. 29 C.F.R. § 778.114(b).

Example:
An employee is paid a monthly salary that in February translates to a weekly salary of $500. However, the employee works irregular hours. In week one, the employee works 40 hours. No overtime is due and the employee is paid $500. In week two, the employee works 50 hours. The employee’s regular rate for week two is $10 ($500 divided by 50), and he is entitled to a $50 half-time overtime premium ($10 x ½ x 10). The employee’s total compensation for week two equals $550. In week three, the employee works 40 hours and is entitled to no overtime. In week four, the employee works 48 hours, resulting in a regular rate of $10.41 per hour ($500 divided by 48). The employee is entitled to a half-time overtime premium of $41.64 ($10.41 x ½ x 8). The employee’s total compensation for week four is $541.64. The employee’s salary plus overtime premiums for the month total $2,091.64.