ABA routing number – definition and meaning

The ABA routing number is a unique code that exists on a check that the ABA (American Bankers Association) assigns. The ABA routing number identifies the financial institution that issued the check.

Banks and other financial institutions based in the USA that own accounts at the Federal Reserve Bank – the country’s central bank – use the 9-digit-code ABA routing number. They use it to process check transactions, including clearance and deposits.

Put simply, the nine-digit code identifies banks in the US. This helps other banks and financial institutions transfer money to and from a customer’s account for transactions like automatic bill payments or direct deposits.


ABA Routing NumberAccording to UC San Diego: “The ABA routing number is a unique, 9 digit identifying transit number assigned to each bank.” (Image: adapted from Bank of America Corporation website)


What is my ABA routing number?

How do I know what my ABA routing number is? There are several ways we can get this information. The easiest and fastest is by looking at the bottom of your check book (US Spelling: Check book. British Spelling: Cheque book),  in the bottom left-hand corner.

In some computer-generated checks, the nine-digit number may appear elsewhere on the document. The ABA routing number is also the bottom left-hand corner of your deposit slips.



Furthermore, you can also contact your bank and ask them which ABA routing number to use. The majority of financial institutions provide this data online. You may have to log in.

Regarding finding the number online, thebalance.com writes:

“Search your bank’s website for direct deposit forms or Automated Clearing House (ACH) information.”


ABA routing number - what the digits meanThe nine-digits of the ABA routing number contain important information for the financial institution. They facilitate successful transactions. (Data Source: bankroutingnumber.us)


Sometimes there are many ABA numbers

A bank might have many ABA numbers. Therefore it is important to make sure you use the ABA routing number that is specific to your account. This is the one in your check book, deposit slip, or the number they give you if you contact the bank.

Over the past couple of decades, there have been several mergers and acquisitions. Whenever banks merge, the new entity ends up with multiple codes.



If you are not sure what your ABA routing number is, you should check with your bank, just to be safe. The number you use for ordering checks might not be the right one for automatic bill payments or wire transfers.

Routing number format

The ABA routing number consists of nine digits:

– Digits 1 and 2 indicate the type of financial institution.

– 3 and 4 indicate the Federal Reserve Bank district branch.

– 5, 6, 7 and 8 tell us the name of the financial institution where the checking account is held.

– 9 indicates the single check digit.

People use the SWIFT code, also known as the BIC code, which contains from 8 to 11 characters, for international wire transfers.

Video – Validity of ABA routing number

In this video, Professor McComb explains how you can determine whether a routing number is a valid one.