Interest on delayed service tax clarified: treat spanning parts of two months as a single monthly interest period. Clarification: interest under Section 75 for delayed service tax is simple interest charged for the period of delay; where payment falls on the first day of the next month after a mid month due date, the delay should be treated as a single month measured from the day after the due date of the first month to the due date of the next month, and interest charged for one month only.