US Banking
American Bankers Association Number
An ABA number is the original name for the nine-digit routing number assigned to US banks by the American Bankers Association. Introduced in 1910 to facilitate check sorting, it was the first standardized bank identification system in the United States. The terms "ABA number," "routing number," and "routing transit number (RTN)" are used interchangeably today.
The ABA number encodes both geographic and institutional information. The first two digits correspond to the Federal Reserve district where the bank is located, and the third and fourth digits identify the Federal Reserve processing center or special designator. The remaining digits identify the specific institution and include a check digit for error detection. You can look up any ABA number using BankCheck to see its district, institution, and validation status.
The ABA numbering system has been in continuous use for over a century and remains the foundation of US payment routing. Understanding its structure helps you verify that a bank is registered and locate which Federal Reserve district processes its transactions. A bank may have different ABA numbers for electronic and paper-based payments.
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