Advance tax interest rules require instalment-specific payments; shortfalls attract staged interest and safe harbour thresholds for compliance relief.
Section 425 imposes interest where advance tax instalments fall short of prescribed percentages by due dates, tying liability to tax due on the returned income. It prescribes staged instalment percentages and graduated interest on interim versus final shortfalls, provides two early safe harbour minima that eliminate interest if met, treats certain classes (profits declared under specified entries) with a distinct simple interest rule for the final instalment, and exempts shortfalls from interest for specified late arising incomes if taxed by later instalments or by 31 March.