IMPS: instant transfers around the clock

IMPS was India's first truly instant account to account transfer system. It was launched by NPCI before UPI existed, and it lets a customer move money to any bank account in India at any time, including nights, weekends, and bank holidays. The payer can address the payment with a mobile number and MMID, or with an account number and IFSC. The transfer is settled immediately and the beneficiary account is credited within seconds. IMPS fits when a payment cannot wait for the next NEFT batch, when the amount is above the comfort zone for UPI, or when the channel does not support UPI. IMPS works on a real time model, not a batch model. Each transaction is processed individually as it arrives, and NPCI operates the IMPS switch that connects the sending bank and the receiving bank. The sending bank debits the payer, the receiving bank credits the payee, and the interbank settlement happens through the settlement accounts banks hold with the Reserve Bank of India. Because the service never sleeps, banks must keep their IMPS interfaces available at all hours, and operations teams must handle failures at 3 in the morning just as well as at 3 in the afternoon. A single IMPS transfer moves through five clear steps. Step one, the payer enters the beneficiary details and the amount in internet banking, mobile banking, or at a branch, and confirms the instruction. Step two, the sending bank validates the instruction, checks the balance, debits the payer, and sends the transfer instruction to the NPCI switch. Step three, NPCI validates the message and routes it to the receiving bank. Step four, the receiving bank checks the beneficiary account and credits it immediately. Step five, the receiving bank confirms back through NPCI, and the payer sees a success message with a transaction reference. The transfer is only complete when the confirmation comes back. Two addressing modes cover most IMPS payments. Person to person mode uses the beneficiary mobile number with an MMID, a seven digit code that identifies the beneficiary bank account, and it is useful when the payer does not know the account number. Person to account mode uses the account number with IFSC, which is the more common mode for business payments. Confirm which modes the project channel supports, because a flow built around mobile number and MMID fails for a corporate payer who only has account numbers. A timeout is the most important exception in IMPS. A timeout happens when the receiving bank or the switch does not respond in time, so the sending bank cannot confirm whether the credit happened. The status is pending, and the sending bank must check the transaction status with NPCI before doing anything else. If the status check shows the credit happened, the bank shows success. If the status check shows the debit happened but the credit did not, the bank must reverse the debit to the payer. If the payer retries without a status check, the same payment can be debited twice. Other failures reject the instruction before any debit: insufficient funds, an invalid account number, a closed beneficiary account, or an amount above the bank limit. A reversal in IMPS follows a fixed path. When a debit succeeds but the credit fails, the receiving bank or the switch reports the failure, and the sending bank posts a reversal credit to the payer account using the original transaction reference. The reversal is not a new payment, it is linked to the original transfer, so reconciliation must match the reversal against the original reference and amount. Where the status is genuinely unknown after a timeout, the bank must resolve it through the status check and the NPCI dispute process rather than guessing. The customer message must cover each outcome: success, failure before debit, pending with a status check in progress, and reversed. The scheme rules set the limits an analyst must check. IMPS runs 24 hours a day, 7 days a week, and credits in seconds under normal conditions. Many banks allow five lakh rupees per transaction through internet and mobile banking, with lower limits on some channels and higher limits for corporate customers. Charges are usually higher than NEFT because of the instant service, and banks publish a slab based fee, so check the current limit and charge for the specific bank and channel rather than hard coding a number. A payment above the IMPS limit needs a clear error message that tells the customer to use NEFT or RTGS instead of a generic failure notice.