Total input tax credit governs interest calculation for wrongful IGST availment; interest applies only where combined ledger falls short. Total input tax credit across IGST, CGST and SGST in the electronic credit ledger is to be treated as the available balance for computing interest on wrongful availment and reversal of IGST credit under rule 88B(3) and section 50(3). No interest arises if, from availment until reversal, the combined ITC balance never falls below the wrongly availed amount; when it does fall below, the extent of deemed utilization equals the shortfall and interest is chargeable to that extent. Compensation cess credit is excluded from this calculation.