Learn About ABA Numbers: Where to Find Them and How They Work

A sample check with the ABA/routing number highlighted
The ABA/routing number, highlighted above, identifies your financial institution.

An ABA number, also known as a bank routing number, is a nine-digit code that identifies banks in the United States. The code helps other banks transfer money to and from checking accounts for transactions like direct deposit and automatic bill payments.

Find and Use ABA Numbers

You can get your account’s ABA number from several sources. If you have a checkbook handy, the easiest approach might be to look at the bottom of one of your checks.

On paper checks: The ABA number is printed on every check. It is usually the nine-digit number in the bottom left-hand corner (although it might appear elsewhere on computer-generated checks). The ABA number is highlighted in the image above, (view larger). Your ABA number can also be found on your deposit slips in the same location.

Contact your bank: You can also contact your bank and ask which ABA number to use. Some banks provide this information online, although you might need to be logged in to find the right number. Search your bank’s website for direct deposit forms or Automated Clearing House (ACH) information.

Use the correct number: Your bank may have several ABA numbers, so it’s essential to use one specific to your account. That’s the same number you’ll find printed on your checks (or the one they provide if you call in and ask). ABA numbers may differ depending on where you opened your account, and bank mergers can result in multiple codes for the same bank.

When in doubt, ask your bank which number to use. Even if you know the correct number for ordering checks, you might need to use a different number for wire transfers and electronic bill payments.

How ABA Numbers Work

For the most part, all you need to do is copy your ABA number and provide it to whoever is asking for it—you don’t need to know anything more about these numbers.

However, if you’re curious, ABA numbers use a fascinating system.

Behind the name: The ABA number is like an address that tells everybody where to find your account. As a result, ABA numbers may also be called routing transit numbers (RTNs). “ABA” is used because the American Bankers Association (ABA) assigns the numbers to banks. The ABA established ABA numbers in 1910 when each bank was assigned its own unique number. Most people outside the banking industry refer to them simply as the bank routing numbers.

Computer-readable: Routing numbers are typically printed on checks using magnetic ink, which allows special machines to read the code more easily. Whether or not magnetic ink is used, the numbers are printed in MICR font, making it easy for computers to read the numbers (when you deposit a check by snapping a photo with your mobile device).

The first four digits were initially assigned by the Federal Reserve Routing System and represent the bank's physical location. Because of acquisitions and mergers, these numbers frequently have no correlation to the bank’s geographic location today. 

The fifth and sixth digits designate which Federal Reserve bank the institution's electronic and wire transfers will route through.

The seventh digit denotes which Federal Reserve check processing center was initially assigned to the bank. 

The eighth digit designates which Federal Reserve district the bank is in. 

The ninth digit provides a checksum. The checksum is a complicated mathematical expression using the first 8 digits. If the end result does not equal the check sum number, the transaction is flagged and rerouted for manual processing.

Note: Erin O’Neil wrote valuable content for this article, in particular covering the origin and the use of each digit.