What are ABA numbers used for?

ABA numbers, also known as routing numbers, serve as a unique identifier for financial institutions in the United States. They are primarily used to identify the specific bank branch where an account is held, facilitating the processing of various transactions such as checks and electronic funds transfers. Each ABA number corresponds to a particular bank, allowing for accurate routing of payment and financial transactions through the banking system. This identification process is crucial, especially in the context of federal regulations and ensuring that funds are transferred to and from the correct institutions efficiently.

While some of the other options might seem relevant to banking operations, they do not accurately describe the primary function of ABA numbers. For example, calculating interest on accounts, verifying account balances, or tracking electronic transfers are managed through different methods and systems within the banking protocol, not through the use of ABA numbers. Therefore, the correct choice highlights the essential role ABA numbers play in identifying bank branches and their locations.