Determination of tax evasion through fraud triggers assessment, interest and escalating penalties with opportunities for voluntary payment to conclude proceedings. Where fraud, wilful misstatement or suppression results in tax not paid, short paid, erroneously refunded or wrongly availed input tax credit, the proper officer must serve a show cause notice requiring payment of the specified tax with interest and a penalty equal to the tax; notices must be issued at least six months before the outer time limit. Voluntary pre-notice or prompt post-notice payments with prescribed reduced penalties can conclude proceedings, and the officer must determine amounts after considering representations within the statutory limitation period.