Advance tax liability: AO can require payment and compute tax using the higher of assessed or return-declared income. Assessing Officer may order payment of advance tax if a liable taxpayer has not paid or has underpaid; the order must state the amount and instalments and be issued during the previous year but before 1 March. For computation the AO takes the higher of the total income of the latest previous year for which an assessment is complete or the total income declared by the assessee in any subsequent return, and computes tax on that amount at prevailing rates.