Customs interest and refund rules govern final assessment liabilities and delayed refunds under provisional assessment. Interest is payable on amounts due to the Central Government after final assessment and on refundable amounts not refunded within three months of final assessment. The importer or exporter must pay interest on any amount payable to the Government from the first day of the month of provisional assessment until payment, at the rate fixed under the customs interest provision. Delayed refunds attract interest until refund, and refund with interest is payable to the importer or exporter where the duty relates to non-passed-on incidence, personal-use imports, buyer-borne duty not passed on, export duty, or drawback of duty.