Interest on delayed duty payments: government-fixed rates apply; exemption for full voluntary payment after Board direction. Interest on delayed payment of excise duty is payable by the person liable for duty in addition to the duty itself, whether paid voluntarily or after determination under section 11A. The Central Government may, by notification, fix the interest rate within a prescribed range, and interest is calculated from the date the duty becomes due until actual payment in terms of section 11A. No interest is payable where duty results from a Board order under section 37B and the full amount is voluntarily paid within the time permitted, without reserving the right to appeal.