What Is an ABA Number?

how ABA numbers work

The Balance

An ABA number, also known as a bank routing number, is a nine-digit code that identifies banks in the U.S. That number makes it possible for banks to transfer money to and from customers' accounts for transactions like wire transfers, direct deposit, and automatic bill payments. You can find it printed on your personal checks.

Key Takeaways

  • An ABA number identifies financial institutions so they can conduct transactions such as wire transfers and direct deposits.
  • ABA numbers have nine digits that you can usually find in the bottom left-hand corner of a personal check.
  • An ABA number is also referred to as a bank's routing number.
  • The American Bankers Association (ABA) created ABA numbers in 1910.
  • Banks can have more than one ABA number based on their branch locations.

How To Find and Use ABA Numbers

You can get your account’s ABA number from several sources. The easiest solution is to locate the numbers at the bottom of one of your checks if you have a checkbook handy.

On Paper Checks

An ABA number is printed on every check. It's usually the nine-digit number in the bottom left-hand corner on personal checks. The number might appear somewhere else on computer-generated checks (like online bill payment checks or business checks).


You can also find your ABA number on deposit slips, typically in the same location.

Contact Your Bank

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. Alternatively, call customer service and ask.

Use the Correct Number

Your bank may operate under several ABA numbers, so it’s essential to identify the one specific to your account. ABA numbers may differ slightly depending on where you opened your account, and bank mergers can result in multiple codes for the same bank. Some banks also use separate ABA numbers for wire transfers vs. direct deposit or ACH transactions.

You might have to use a different number for wire transfers or electronic bill payments even if you know the correct number for ordering checks. When in doubt, ask a customer service representative at your bank which number to use.

How ABA Numbers Work

All you have to do is provide your ABA number, along with your account number, to whoever is requesting it in most cases. Banks, billers, and your employer (or whoever else is setting up automatic transfers) can handle the logistics after that.


You may receive new ABA numbers if your bank fails or merges with another bank, 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. You can continue using old routing numbers indefinitely in some cases.

ABA numbers follow an intricate system:

Behind the Name

An ABA number is like an address that tells financial institutions where to find your account. ABA numbers may also be called routing transit numbers (RTNs) or check routing numbers for this reason.

They're Computer-Readable

Routing numbers are typically printed on checks using magnetic ink, which allows special machines to read the code more easily. Printers usually use MICR font regardless of whether magnetic ink is present, making it easy for computers to visually recognize the numbers. This can be helpful when you deposit a check by snapping a photo with your mobile device.

The first four digits are made up of the Federal Reserve Routing Symbol. The first two digits have different meanings based on their series. The ABA outlines each series on its website.

The next four digits are the ABA institution identifying digits.

The ninth digit provides a checksum or check digit. This is a complicated mathematical expression using the first eight digits. The transaction gets flagged and rerouted for manual processing if the end result does not equal the checksum number.

History of the ABA Number

The American Bankers Association (ABA) created ABA numbers in 1910 as a way to assign unique identifiers to each payment-issuing bank. Doing so reduced confusion for processing paper checks, which were the common form of payment at the time. ABA numbers have evolved over time to include the Federal Reserve’s payment processes and facilitate modern electronic payments.

How ABA Numbers Help Process Checks

The ABA number has played an instrumental part in speeding up check processing since the 1960s. Additionally, physical checks that needed to travel by airplane and truck to reach banks could now be submitted and cleared electronically with the passage of the Check 21 Act in 2003. Funds clear much more quickly as a result, and consumers no longer have the luxury of "playing the float" or issuing a check a few days before they actually have the funds in their account.

Frequently Asked Questions (FAQs)

How can you tell the difference between a routing number and an account number?

The routing number is usually the first, bottom-left number on your check and is followed by the account number. The routing number is always nine digits long, while your account number may be between 10 and 12 digits.

What is the difference between an IBAN number and an ABA number?

IBAN numbers, or international bank account numbers, are used for international bank routing throughout much of Europe. ABA numbers are specific only to the U.S. The U.S. does not use IBAN numbers for international banking. The U.S. uses SWIFT codes for international transfers.

How do I find my bank routing number without a check?

You can call your bank or check its online banking website for the information. The ABA also provides a lookup tool on its website.

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The Balance uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Bank. "Find Your U.S. Bank Checking Account Routing Number."

  2. Bank of America. "Routing Number FAQs."

  3. Xerox. "Generic MICR Fundamentals Guide." Page 1-5.

  4. American Bankers Association. "Routing Number Policy & Procedures."

  5. FRASER, Federal Reserve Bank of St. Louis. "8203. Addition of the Check Digit in the Routing Number Field on Checks."

  6. American Bankers Association. "ABA Routing Number."

  7. Board of Governors of the Federal Reserve System. "Regulation CC (Availability of Funds and Collection of Checks): Frequently Asked Questions About Check 21."

  8. Board of Governors of the Federal Reserve System. "The Federal Reserve in the Payments Mechanism." Page 11.

  9. Bank of America. "Wire Transfers FAQs."

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