Bank account numbers in the United States don't follow any account number standards from one institution to the next, although the system that handles electronic payments limits the overall length of account numbers. However, dozens of other countries, mostly in Europe and the Middle East, have adopted a common standard for account numbers that makes international or cross-border transactions go smoothly.
ACH Numbering Limitation
U.S. banks are free to use any numbering system they want for their bank account numbers. However, if those accounts are going to send and receive electronic payments, then the number cannot be more than 17 digits long. That limit comes from the Automated Clearing House (ACH), the computer network that handles transactions such as direct deposits and direct-debited bill payments. The ACH software accepts account numbers only up to 17 digits, so that's the limit for "ACH-enabled" accounts.
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Bank Routing Numbers
Although bank account numbers are not standardized, the routing numbers that identify the banks themselves do follow a set formula. This ensures that transactions get submitted to the correct banks; from there, the bank applies the transaction to the specified account. Routing numbers are always nine digits long.
The first two digits indicate the Federal Reserve district where the bank is located. There are 12 districts: Boston, 01; New York, 02; Philadelphia, 03; Cleveland, 04; Richmond, Va., 05; Atlanta, 06; Chicago, 07; St. Louis, 08; Minneapolis, 09; Kansas City, Mo., 10; Dallas, 11; and San Francisco, 12. If the "bank" is actually a thrift, such as a credit union or savings and loan, the first digit will be increased by 2 – so 22 would be a thrift in the New York district, and 32 would be a thrift in the San Francisco district.
International Bank Account Number
In Europe, where payments cross national borders regularly, countries have adopted a standard format for account information, the International Bank Account Number. Each IBAN begins with a two-letter country code, such as FR for France or BE for Belgium, followed by two "check digits" that are used to validate the account. Those characters are followed by as many as 30 digits that identify the specific bank and account. Each country decides for itself how many digits it will use and what those digits indicate. The country code then tells you how to interpret the digits.
Non-European IBAN Countries
Most countries in Europe use IBAN format, and the format has spread to several other nations: Israel, Kazakhstan, Kuwait, Lebanon, Mauritius, Saudi Arabia and Tunisia. There are, however, many of the world's countries, including the United States, that do not participate in the IBAN system, although the format is designed to allow global implementation.
International Transfers From the U.S.
Although a country may not participate in the IBAN system, banks in non-IBAN countries are still able to transact with countries that do use IBAN. In order to initiate an international transfer, you will need the recipient's information including the account type, an IBAN and the receiving bank's bank identifier code (BIC) or Society for Worldwide Interbank Financial Transactions (SWIFT) code. The BIC or SWIFT code is much like a routing number in the US and specifies which bank is to receive the transfer. If you're unsure how to initiate an international transfer from the US, call your bank's customer service number or visit a local branch for assistance.