SAP Help Function module DATE_COMPUTE_DAY is used to calculate what day of the week a date is
DATE_COMPUTE_DAY sap function module
The below code shows how function module DATE_COMPUTE_DAY is used to calculate the day of the week a particular date is (1=Monday, 5=Friday etc..).
Calculate day of week DATA: ld_day TYPE c. CALL FUNCTION 'DATE_COMPUTE_DAY' EXPORTING date = sy-datum IMPORTING day = ld_day.