HDFC BANK has branches in 36 states.
Indian Financial System Code (IFSC). It is used for electronic payment applications like Real Time Gross Settlement (RTGS), National Electronic Funds Transfer (NEFT), Immediate Payment Service, an interbank electronic instant mobile money transfer service (IMPS), and Centralised Funds Management System (CFMS) developed by Reserve Bank of India (RBI).
Code has eleven characters "Alpha Numeric" in nature.
First four characters represent bank, fifth character is default "0" left for future use and last six characters represent branch.
Here in this IFSC code HDFC0001821 where bank char is HDFC and branch is 001821.
MICR Code: Magnetic Ink Character Recognition as printed on cheque book to facilitate the processing of cheques.
