Interest on delayed tax requires taxable persons to self-assess and pay interest for unpaid tax periods and excess ITC claims. Persons liable to pay tax who fail to pay tax within the prescribed period must pay interest on the unpaid amount at a Government-notified rate not exceeding eighteen per cent., calculated from the day after the due date in the prescribed manner; persons making undue or excess input tax credit claims or undue reductions in output tax liability must pay interest on those amounts at a Government-notified rate not exceeding twenty-four per cent.