Waiver of interest allows tax officers to reduce or waive advance-tax interest in specified circumstances, with limited temporal scope. Rule 40 authorises reduction or waiver of interest payable under the advance-tax provisions where specified circumstances justify relief: assessment delayed more than one year through no fault of the assessee; assessment of an agent on another's income; income from an unregistered firm assessed under the relevant provision; unforeseen large end of year profits; and cases where the Deputy Commissioner deems waiver justified, subject to a temporal exclusion for assessments from the assessment year beginning April first, 1989.