Provisional assessment allows provisional tax payment pending documents; finalization triggers additional tax, interest and refund conditions. Provisional assessment allows an assessee to pay service tax provisionally when actual liability cannot be determined and requires a written request to the Assistant or Deputy Commissioner; the officer may fix provisional value and the assessee must file a Form ST-3A memorandum with periodic returns. Finalization must occur within six months (with permitted extensions) after the provisional order and may result in additional tax with interest under section 11AA or refund with interest under section 11BB, subject to unjust enrichment rules and possible credit to the consumer welfare fund.