Interest on wrongly availed IGST credit depends on the combined ITC balance across IGST, CGST and SGST heads. The total ITC balance in the electronic credit ledger-aggregating IGST, CGST and SGST-must be used to determine whether wrongly availed IGST credit was utilized; no interest is chargeable if the combined ITC balance never fell below the wrongly availed amount between availment and reversal, but when the combined balance falls below that amount the shortfall measures utilization and attracts interest. Compensation cess credit is excluded from the aggregation and cannot be used for this purpose.