What is Routing Number?

A routing number is a nine-digit identifier assigned to U.S. financial institutions by the American Bankers Association (ABA) and registered with the Federal Reserve. It serves as the address of the institution within payment networks, directing funds to the correct bank during ACH transfers, wire transfers, check processing, and direct deposits. The routing number appears as the first set of numbers at the bottom left of a paper check, followed by the account number and the check number.

The nine digits encode specific information. The first two digits indicate the Federal Reserve district in which the institution is located. The next two digits identify the Federal Reserve Bank or branch that serves the institution. The fifth through eighth digits are the institution's unique identifier within that district. The ninth digit is a check digit computed using a modulus algorithm to validate the full routing number.

Routing numbers are public information and are available on bank websites, printed on checks and deposit slips, and through the Federal Reserve's online directory. Financial institutions may maintain multiple routing numbers (such as one for paper and electronic transactions, another for wire transfers, and potentially others for different regions or processing centers). Consumers setting up direct deposit, automatic bill payments, or wire transfers must provide the routing number specific to the transaction type and their account.

When financial institutions merge or undergo acquisitions, their routing numbers can change, necessitating updates to direct deposits and automatic bill payments. While the acquiring bank typically supports legacy routing numbers during a transition period (often twelve to twenty-four months) to prevent check rejections and payment failures, consumers must eventually update their payroll and merchant agreements with the new routing transit number. Additionally, because banks routinely utilize separate routing numbers for ACH transactions and wire transfers, sending a domestic Fedwire transfer using a bank's ACH routing number will result in the transaction being rejected or delayed, making it critical to confirm the precise routing details with the bank beforehand.