Interest on delayed GST payment: calculate on unpaid tax or on amounts debited from electronic cash ledger during delay. Rule 88B requires that interest on delayed GST payments be calculated on the tax amount paid by debiting the Electronic Cash Ledger for the period of delay when returns are filed late, except where credited amounts present on or before the due date remain in the ledger until debit. In other cases, interest runs on unpaid tax from the due date until payment. Interest on wrongly availed input tax credit is computed from the date of its utilisation-when the credit ledger balance falls below the wrongly availed amount-until reversal or payment.