ABA routing number – definition and meaning

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

The ABA routing number, a nine-digit code, is used mainly by banks and other financial institutions based in the United States that own accounts at the country’s central bank – the Federal Reserve Bank – to process check transactions, including clearances and deposits.

Put simply, the nine-digit code identifies banks in the US, which 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 this information can be obtained – the easiest and fastest is by looking at the bottom of your check book (US Spelling: Check book. British Spelling: Cheque book). It is printed on each paper check, in the bottom left-hand corner.

In some computer-generated checks, the nine-digit number may appear elsewhere on the document.

If you look at the bottom left-hand corner of your deposit slips, you should see your ABA routing number there too.



If you don’t have a check book or deposit slip, you should 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 so that it can carry out a successful transaction. (Data Source: bankroutingnumber.us)

Sometimes there are many ABA numbers

A bank might have many ABA numbers. 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 and give them your details.

In the world of banking and finance over the past couple of decades, there have been several mergers and acquisitions. Whenever financial institutions 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. Sometimes 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.

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

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

– Digit 9 indicates the single check digit.

The SWIFT code, also known as the BIC code, contains from 8 to 11 characters and is used 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.