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Have you ever wondered what those numbers on the bottom of your check represented? In the bottom middle is your account number and the check number, but what is the nine-digit number on the bottom left? Here is a description of this ABA number found on all checks.

What is an ABA Number?
In 1910, the American Bankers Association (ABA) created the ABA Routing Transit Number (ABA RTN) system. This has assigned a unique ABA number to all United States financial institutions. Just as your automobile has a license number, your check has a routing transit number.

When you buy something with a check, you give the merchant an IOU. The merchant can then deposit that check in his or her merchant account. Your account will be debited and the merchant account will be credited by the check amount.

Why is the ABA RTN so important?
All financial transactions require reconciliation. At the end of the night, financial institutions collect all of the paper and electronic documents and record the credits and debits for that day. The nine-digit ABA RTN identifies the location of your bank merchant account.

What is Accuity?
“Accuity” is the official ABA Registrar of Routing Numbers. Accuity publishes a semi-annual guide to the ABA RTN system documenting the additions, removals and updates. New financial institutions must submit applications to Accuity for assignment of their own routing transit number. In 2015, there were more than 25,000 ABA numbers.

How Does the Federal Reserve System Fit In?
In 1913, the Federal Reserve took over management of many portions of the American money supply. Reconciliation of financial instruments takes place at the Federal Reserve member banks. Over time, the ABA number has been updated for usage with modern payment systems (i.e. wire transfers and credit card processing).

Another upgrade involved the creation of the Magnetic Ink Character Recognition (MICR) number. This ABA number is rendered in a format that is machine-readable. If you look at your paper check, you will find two ABA RTN forms: 1. Fraction (upper right by date) and MICR (lower left).

The modern ABA number is available in both paper and electronic formats to facilitate credit card processing, automated clearinghouses (ACH), electronic funds transfer (EFT) and on-line banking. The ABA RTN is your bank’s official ID.