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ABA Numbers: Where to Find Them and How They Work

ABA Number is a nine-digit sequence used by banks to identify a financial institution in the United States. ABA Number might also be known as check routing numbers or routing system numbers (RSNs).

ABA (American Bankers Association) numbers help you make transactions within banks and accounts, transfer and receive money, pay bills, make wire transfers, direct deposit. 

ABA Number

Why Were ABA Numbers Introduced?

ABA Numbers, also known as routing numbers, have been around for half of the century as it has been introduced in 1910. American Bankers Association introduced ABA Numbers, so there would be less confusion in cashing checks. 

In 1910, banks were booming. By 1920 there were nearly 30 000 different banks in the United States, and it was more than in the rest of the world all unitedly.

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At the time, many banks shared a similar name, therefore American Bankers Association (ABA) wanted to avoid situations when cheks written by American Bank would be withdrawn from American Bank (which is a different institution with a similar name). 

Each bank was provided with a publicly-known routing number which would be identified amongst financial institutions and make the process of transactions smooth and convenient. 

Where To Find ABA Numbers?

Usually, ABA Numbers are located on the left side at the bottom of your check. However, you can find an ABA Number in different sources.

Paper Checks

The easiest way of identifying an ABA Number is by finding it on your paper check. It usually appears in the same place, as mentioned: on the left side at the bottom of your check.

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When computers generate a check, for example, a payment bill, it may appear in different places. In such a case, make sure to double-check it with your bank. 

Find It Via Your Bank

Normally banks’ websites publish such information online, so it is not confusing nor difficult to find. To find it online, you might need to log in to your bank account. However, you can also find it in Automated Clearing House (ACH) information or direct deposit forms.

If you can’t find an ABA Number, do not hesitate to call the customer service of your bank!

Banks might have many ABA Numbers on their website, however, make sure you use the one that says ABA routing number, which is specific for your account. 

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How Do ABA Numbers Work?

You need to know your ABA Number to provide it together with an account number, once requested. Usually, you need to provide an ABA Number (with an account number) for your employer, bank, or biller.

The structure of an ABA number indicates the physical location, of your bank, ABA institution code, and checksum. 

  • Characters 1-4: these digits were provided by Federal Reserve Routing System and they mainly indicate the bank’s physical location. 
  • Characters 4-8: show ABA institution code, or to be more precise, it presents which Federal Reserve bank transfers will route through. 
  • Character 9: it provides a checksum, also known as a check digit. This number ensures that all the previous digits were typed correctly. It may sound surprising, but one digit can check the correctness of the previous eight numbers. It uses a Luhm algorithm which is a complex mathematical expression. However, it helps the transaction get flagged or be checked manually if a sender types ABA Number incorrectly. 
ABA Routing Number Structure


ABA Number is a nine-digit sequence that you can easily find on your check. It is located on the left side at the bottom of the check.

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The number was introduced in 1910. American Bank Association started usage of such numbers to make transactions and cash withdrawals easier and more convenient.