Interest on delayed refunds: statutory simple interest payable when a refund is not issued within the prescribed period. Section 243 requires payment of simple interest on refunds not granted within the prescribed three month period, calculated from the day after that period until the refund order is made. Periods of delay attributable to the assessee are excluded from interest, and questions about excluded periods are finally determined by the Principal Chief Commissioner/Chief Commissioner or Principal Commissioner/Commissioner. An amendment disapplies the section for assessments from the assessment year beginning April 1989 onward.