ABA numbers are routing codes that tell banks where to send your money
An ABA number is a nine-digit code that identifies which bank or credit union holds an account. Banks use it to route money to the correct financial institution during transfers, direct deposits, and bill payments. The code is also called a routing number or routing transit number (RTN). Every bank in the United States has at least one ABA number, and some large banks have multiple codes for different regions or branches.
The term "ABA" comes from the American Bankers Association, the organization that originally created and maintains the numbering system. When you set up direct deposit at work, pay a bill by bank transfer, or send money to another person's account, the ABA number ensures the money reaches the right place. Without it, the banking system would have no standard way to identify which of thousands of financial institutions should receive the funds.
You will see your ABA number on checks, in your bank's online portal, and in your account statements. It is not secret information — banks publish these numbers publicly so people can send money to accounts at their institution.
Key Takeaways
- An ABA number is a nine-digit routing code that identifies your bank or credit union and directs money transfers to the correct institution.
- You need your ABA number and account number together to receive direct deposits, wire transfers, and ACH payments from other banks.
- The first four digits of an ABA number identify the Federal Reserve district, and the next four identify the specific bank.
- You can find your ABA number on the bottom left of your checks, in your online banking portal, or by calling your bank.
- ABA numbers are public information and are safe to share with employers, bill payment services, and anyone sending you money.
How the nine-digit ABA code breaks down
The nine digits in an ABA number follow a specific pattern that tells the banking system where to route the money. The first four digits identify which Federal Reserve district the bank operates in — for example, banks in New York have different opening digits than banks in California. The next four digits identify the specific bank or credit union within that district. The final digit is a check digit that the banking system uses to verify the number is correct and catches typos.
For example, if your ABA number is 021000021, the "0210" tells the system the money is going to a bank in the New York Federal Reserve district, the "0002" identifies the specific bank, and the final "1" is the check digit. This structure has remained the same since the American Bankers Association created it in 1910, which is why the system still works reliably today even though banking has changed dramatically.
Large banks often have multiple ABA numbers because they operate in different regions or have different divisions. Bank of America, for instance, has dozens of routing numbers depending on which state your account is in. This does not mean you have multiple numbers — you have one ABA number for your specific account at your specific branch or region.
Where you need an ABA number and where you do not
You need your ABA number and account number together whenever money is moving from one bank to another. This includes direct deposit from your employer, automatic bill payments from your checking account, wire transfers you send or receive, and ACH transfers (the standard electronic transfer method used by most banks). If someone outside your bank is sending you money, they will ask for both numbers to make sure it lands in your account.
You do not need an ABA number for transactions within the same bank. If you transfer money between your own checking and savings accounts at the same institution, the bank handles it internally and does not need a routing code. You also do not need it for debit card purchases, credit card payments, or ATM withdrawals — those transactions do not involve routing money between different banks.
When you write a check, the ABA number is printed on it in magnetic ink at the bottom left, but the person cashing the check does not need to know or use it. The bank that processes the check reads the number automatically. However, if someone wants to set up a direct deposit or automatic payment using your checking account, they will need to manually enter your ABA number and account number.
How to find your ABA number
The easiest place to find your ABA number is on a check from your account. Look at the bottom left corner — you will see nine digits printed in a special magnetic ink format. The first nine digits are your ABA number. If you do not have checks or prefer not to look them up that way, log into your online banking portal and search for "routing number" in the account information or settings section. Most banks display it clearly on the account details page.
You can also call your bank's customer service line and ask for your routing number. Have your account number ready when you call. Some banks also list routing numbers on their website — you can search "[Your Bank Name] routing number" and usually find a page with codes for different regions or account types.
If you are unsure whether you have the right number, the Federal Reserve maintains a public database of all ABA numbers. You can search it at the Federal Reserve's website to confirm a routing number belongs to the bank you think it does. This is useful if you received a number from someone else and want to verify it before using it for a large transfer.
Why banks use ABA numbers instead of other systems
The ABA routing system has been the standard in the United States for over a century because it is reliable, widely understood, and built into every bank's infrastructure. When the American Bankers Association created it in 1910, there was no other way to sort and route checks and payments between thousands of banks. The system was designed to work with the physical check-clearing process, and it has been updated to work with electronic transfers as well.
Other countries use different systems — the United Kingdom uses sort codes, Canada uses institution numbers, and many European countries use IBAN (International Bank Account Number) codes. The United States has stuck with ABA numbers because switching to a different system would require updating every bank's computer systems, retraining staff, and coordinating across the entire financial industry. The cost and disruption would be enormous, so the existing system persists even though newer alternatives exist.
The ABA system also works well because it is simple and standardized. Every bank knows how to read and use these nine-digit codes, and the format has not changed in decades. This consistency means that direct deposits set up in 1995 still work the same way today, and a transfer between any two banks in the country will work reliably without special software or agreements.
What happens if you give the wrong ABA number
If you provide an incorrect ABA number, the money will be sent to the wrong bank. Depending on how wrong the number is, one of two things usually happens. If the number is close to a real ABA number but not quite right, the receiving bank may reject the transfer and send it back to the sender with an error message. This takes a few business days, and the sender will be notified that the transfer failed.
If the number happens to match a real bank but is not your bank, the money may arrive at that bank but will not be deposited into any account because the account number will not match anything in their system. The receiving bank will then return the funds to the sender. In either case, you will not receive the money, and the sender will have to try again with the correct information.
The check digit (the last digit of the ABA number) is designed to catch simple typos. If you accidentally transpose two digits or type one digit wrong, the check digit validation will usually catch it and the transfer will fail before the money is sent. This is a safety feature built into the system. However, if you provide a completely different but valid ABA number, the system cannot tell that it is wrong, and the money will go to the wrong bank.
ABA numbers and your financial security
ABA numbers are public information and sharing them is safe. Banks publish routing numbers on their websites and in public directories specifically so people can send money to accounts at their institution. Giving your ABA number to your employer for direct deposit, to a utility company for automatic bill payment, or to anyone else who needs to send you money does not put your account at risk.
However, you should never share your full account number with people you do not trust. Your ABA number alone cannot be used to withdraw money or access your account — someone would need both your ABA number and your full account number to do that. Even with both numbers, they still cannot access your account without additional authentication. Your bank will not allow transfers or withdrawals based on routing and account numbers alone; they require a signature, PIN, password, or other verification.
If you are concerned about a transfer request, you can always call your bank directly to verify that the request is legitimate before providing any information. Banks have fraud detection systems that monitor for unusual transfers, and they will contact you if something looks suspicious.
Frequently Asked Questions
Is my ABA number the same as my account number?
No. Your ABA number (routing number) identifies your bank, while your account number identifies your specific account at that bank. You need both numbers together for transfers between banks. The ABA number is nine digits; account numbers vary in length by bank.
Do I need a different ABA number for checking and savings accounts?
No. Both your checking and savings accounts at the same bank use the same ABA number because they are both held at the same institution. The account number is what distinguishes between them. If you move to a different bank, you will have a new ABA number.
Can I use someone else's ABA number to send them money?
Yes. If you know someone's ABA number and account number, you can send them money through your bank via ACH transfer or wire transfer. The ABA number tells your bank which institution to send the money to, and the account number tells that institution which account to deposit it into.
What if my bank has multiple routing numbers?
Large banks often have different routing numbers for different regions or account types. You should use the routing number specific to your account, which you can find on your checks or in your online banking portal. Using a different routing number for the same bank might cause delays or failed transfers.
Do credit unions have ABA numbers?
Yes. Credit unions are part of the same banking system and have their own ABA numbers. You can find your credit union's routing number the same way you would for a bank — on your checks, in your online portal, or by calling customer service.