What is an ABA number?

An ABA number (also called a routing number or transit number) is a nine-digit code that identifies a U.S. bank or financial institution when money is being moved between accounts. Every domestic payment in the U.S., including direct deposits, bill payments or wire transfers, relies on ABA numbers to route funds to the correct bank.

History of the ABA number 

The American Bankers Association (ABA) created this system in 1910. Today, each bank or credit union in the U.S. has one or more ABA routing numbers, all managed by the Federal Reserve. In total, there are roughly 22,000 active ABA routing numbers in use. These numbers are printed at the bottom of U.S. cheques (checks) and are also used in electronic payments.

Which payments use ABA numbers?

Banks use ABA numbers for domestic payments only. For example, when you set up a US direct deposit or an ACH (Automated Clearing House) transfer, the routing number tells the system which bank will receive the money. The U.S. ACH network now moves over 33.5 billion payments a year, all using ABA routing numbers to link accounts. By contrast, international transfers do not use ABA numbers – instead, they use SWIFT/BIC codes and IBANs to identify banks and accounts overseas.

Why banks use ABA numbers

ABA routing numbers were introduced to make check clearing and electronic payments faster and more reliable. Before computers, each routing number corresponded to a Federal Reserve processing centre to speed up manual check sorting. Today, the system is fully electronic, but the concept remains: routing numbers ensure every transaction ends up at the right bank.

How do ABA numbers work?

When you use online banking to transfer funds to someone’s U.S. account, the ABA number directs your bank to send the money to that specific institution. Routing numbers are essential for many types of payments – wire transfers, direct deposits (like salaries or tax refunds) and automated bill payments. They even appear on the magnetic ink on paper cheques, so machines know where to send the funds.

Because the ABA system is for U.S. banks, you won’t use an ABA number when sending money in other currencies or to non-U.S. banks. For those cross-border payments, you would use a SWIFT/BIC code (and often an IBAN) instead.

Finding your ABA number

If you have a U.S. bank account, finding its routing (ABA) number is straightforward. On a paper cheque, the ABA number is printed in the bottom left corner. It is the first nine digits of the MICR line, immediately followed by your account number. In online banking, most bank apps or websites display the routing number alongside your account details.

A single bank may have multiple routing numbers. Large banks often use different ABA numbers for different regions or for different types of transfers (for example, one routing number for ACH payments and another for wires). Always double-check that you have the correct routing number for the payment type and location.

ABA vs international codes

An ABA routing number is used only for U.S.-domestic transfers. If you are sending money to a U.S. account from another country, or sending money from the U.S. to a foreign bank, you will not use the ABA number alone. Instead, you will provide the bank’s SWIFT/BIC code (its international bank identifier) and an IBAN (if the destination country uses IBANs). The SWIFT/BIC and IBAN system is how banks worldwide recognise each other.

If you were transferring euros from Europe to a U.S. bank, you would need the U.S. bank’s SWIFT/BIC code (to identify the bank internationally) and your U.S. account number, rather than just the ABA number alone. For everyday U.S. transfers, though, just the ABA routing number and the account number are enough.

ABA number stats

In 2024 alone, the U.S. ACH network processed about 33.56 billion payments. Each of those relied on correct ABA routing numbers to reach the intended banks. This volume shows how central these numbers are to the U.S. payment system (for comparison, there are roughly 22,000 active ABA routing numbers in the system, covering all U.S. financial institutions).