Interest on delayed tax payment requires self payment from the day after due; higher interest applies to excess input credit claims. Section 50 requires a person liable for tax who fails to pay within the prescribed period to pay interest on the unpaid tax for the period it remains unpaid, calculated from the day after the tax was due in the prescribed manner. It separately requires interest on undue or excess claims of input tax credit or undue or excess reductions in output tax liability, with the Government notifying higher applicable rates on the Council's recommendation.