Interest on delayed tax payment imposes self-assessed interest for unpaid tax and excess input credit claims. Section 50 requires a person who fails to pay tax when due to pay interest for the period of delay at a rate notified by the Government on the Council's recommendation, calculated from the day after the due date in the prescribed manner. It also requires interest on any undue or excess claim of input tax credit or undue or excess reduction in output tax liability at a government-notified rate, thereby creating parallel interest liabilities for delayed payment and for erroneous or excessive credits or reductions.