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

A sample check with the ABA/routing number highlighted

An ABA number, also known as a bank routing number, is a nine-digit code that identifies banks in the U.S. That number 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 is to read the numbers from the bottom of one of your checks.

On paper checks: An 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 (like online bill payment checks or business checks). For reference, the ABA number is highlighted in the image above, (view larger). You can also find your ABA number on deposit slips—typically 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 log into your account 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 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 a customer service representative at 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

© The Balance, 2018

For the most part, all you need to do is copy your ABA number and provide it to whoever is asking for it—banks handle the logistics for you after that. Provide that number, along with your account number, to your employer or whoever else needs the number for automatic transfers.

If your bank fails or merges, you may get new ABA numbers—but you don’t necessarily have to start using them right away. Ask your bank if you can continue using the old numbers until you order new checks or sign up for new services. In most cases, you can continue using old routing numbers indefinitely.

If you’re curious about how things work, ABA numbers use a fascinating system.

Behind the name: An 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) or check routing numbers. “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 present, the numbers are written in MICR font, making it easy for computers to recognize the numbers (when you deposit a check by snapping a photo with your mobile device, for example).

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 do not correlate with 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 eight digits. If the end result does not equal the checksum 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.