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ROUTING/TRANSIT NUMBER – A nine-digit number, also known as the ABA number, which is used within the banking system to identify a financial institution. The number is used on items (checks, ACH transactions, etc.) that belong to a specific financial institution so that they can be routed through the banking system to the proper institution.

ABA Routing Transit Number

ABA routing transit number (ABA RTN) is a nine-digit code, used in the United States, which appears on the bottom of negotiable instruments such as checks to identify the financial institution on which it was drawn. The ABA RTN was originally designed to facilitate the sorting, bundling, and shipment of paper checks back to the drawer’s (check writer’s) account. As new payment methods were developed (ACH and Wire), the system was expanded to accommodate these payment methods.

The ABA RTN is necessary for the Federal Reserve Banks to process Fedwire funds transfers, and by the Automated Clearing House to process direct deposits, bill payments, and other such automated transfers.

The ABA RTN system was developed in 1910 by the American Bankers Association.

Since 1911, the American Bankers Association has partnered with a series of registrars, currently Accuity, to manage the ABA routing number system.  Accuity is the Official Routing Number Registrar and is responsible for assigning ABA RTNs and managing the ABA RTN system. Accuity publishes the American Bankers Association Key to Routing Numbers semi-annually. The “Key Book” contains the listing of all ABA RTNs that have been assigned.

There are approximately 26,895 active ABA RTNs currently in use.  Every financial institution in the United States has at least one. The Routing Number Policy allows for up to five ABA RTNs to be assigned to a financial institution. Many institutions have more than five ABA RTNs as a result of mergers.

ABA RTNs are only for use in payment transactions within the United States. They are used on paper check, wire transfers, and ACH transactions. On a paper check, the ABA RTN is usually the middle set of nine numbers printed at the bottom of the check. Domestic transfers that use the ABA RTN will usually be returned to the paying bank.

International Wires

Incoming international wire transfers also use a BIC code, also known as a SWIFT code, as they are administered by the Society for Worldwide Interbank Financial Telecommunication (SWIFT) and defined by ISO 9362. In addition, many international financial institutions use an IBAN code.

The IBAN was originally developed to facilitate payments within the European Union but the format is flexible enough to be applied globally. It consists of an ISO 3166-1 alpha-2 country code, followed by two check digits that are calculated using a mod-97 technique, and Basic Bank Account Number (BBAN) with up to thirty alphanumeric characters. The BBAN includes the domestic bank account number and potentially routing information. The national banking communities decide individually on a fixed length for all BBAN in their country.

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