An ABA routing transit number (ABA RTN) is a nine digit code, used in the United States, which appears on the bottom of negotiable instruments such as checks to identify the financial institution on which it was drawn. The ABA RTN was originally designed to facilitate the sorting, bundling, and shipment of paper checks back to the drawer’s (check writer’s) account. As new payment methods were developed (ACH and Wire), the system was expanded to accommodate these payment methods.
The ABA RTN is necessary for the Federal Reserve Banks to process Fedwire funds transfers, and by the Automated Clearing House to process direct deposits, bill payments, and other such automated transfers.
The ABA RTN system was developed in 1910 by the American Bankers Association.
Using and Finding ABA Numbers
How do you know what your ABA number is? You can get this information in several ways, but the easiest way is to look at your checkbook if you have one.
On paper checks: your ABA number is printed on each check. It is usually the nine digit number in the bottom left-hand corner (although it might appear elsewhere on computer-generated checks). In the image above, the ABA number is highlighted in yellow (view larger). The 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 right number: your bank may have several ABA numbers, but you should use the one specific to your account. That’s the one 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.
It’s always safest to 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 automatic 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, there is a fascinating system behind ABA numbers.
The ABA number is like an address that tells everybody where to find your account. ABA numbers are also known as routing transit numbers (RTNs). “ABA” is used because the American Bankers Association (ABA) assigns the numbers to banks.
The numbers are generally 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).
Origin: the ABA established ABA numbers in 1910 when each bank was assigned its own unique number. Today ABA numbers are often referred to as RTN or Routing Transit Numbers. Most people outside the banking industry refer to them simply as the bank routing numbers.
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 banks 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 originally assigned to the bank.
The eighth digit designates which Federal Reserve district the bank is in.
The ninth digit provides a check sum. The check sum 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.