A trace number is a reference attached to an individual payment that allows the banks involved to find it in their records. The term is most closely associated with the United States ACH network. Every ACH entry carries a 15-digit trace number assigned by the originating depository financial institution. The first eight digits are taken from that bank's routing number, and the remaining seven are a sequence number that the bank assigns in ascending order within each batch.
The number travels with the entry to the receiving bank and is quoted in any return or correction, which lets the originator match a returned item to the original payment. When a customer says a direct deposit or payout has not arrived, the sender can give the trace number to the recipient, whose bank uses it to search for the credit. The wider process is described under payment trace.