What is included in an employee's "normal weekly earnings" for the purposes of calculating statutory maternity pay?

An employee's "normal weekly earnings" for the purposes of calculating statutory maternity pay (SMP) are her earnings during the eight-week period prior to her qualifying week (the qualifying week is the 15th week before the expected week of childbirth). Earnings for these purposes include any remuneration on which the employer is liable to pay Class 1 national insurance contributions. They therefore include bonus payments, overtime and commission. Should, for example, the employee receive an annual bonus in this eight-week period, her SMP will be substantially higher than it would otherwise have been. Similarly, if the employee was in receipt of sick pay at a lower rate than her normal earnings during the eight-week period, her SMP will be lower than it would otherwise have been.