What is an ABA routing number?

An ABA routing number (also known as a routing transit number or RTN) is a nine-digit code used in the United States to identify financial institutions. Created by the American Bankers Association in 1910, this number ensures that checks and electronic transfers are directed to the correct bank. Every federally chartered and state-chartered bank in the U.S. that is eligible to maintain an account at a Federal Reserve Bank is assigned a unique ABA routing number.

The nine digits in a routing number follow a specific structure. The first four digits identify the Federal Reserve district and the specific Federal Reserve Bank that serves the institution. The next four digits identify the financial institution itself within that district. The final digit is a checksum that validates the entire number using a weighted algorithm.

Tool description

This validator instantly checks whether an ABA routing number is valid according to the official checksum algorithm. Simply enter a nine-digit routing number, and the tool will verify its mathematical validity. This helps you catch typos and formatting errors before submitting banking information.

How it works

ABA routing numbers use a checksum validation based on a weighted sum algorithm. Each digit is multiplied by a weight (3, 7, or 1 in a repeating pattern), and the results are summed. If the total is evenly divisible by 10, the routing number passes validation. This mathematical check catches most common transcription errors.

Features

  • Instant validation using the official ABA checksum algorithm
  • Detects transcription errors and typos immediately
  • Validates proper nine-digit format
  • No data storage—your banking information stays private
  • Works offline after page load

Use cases

  • Verifying bank details: Double-check routing numbers before setting up direct deposits, wire transfers, or ACH payments to avoid failed transactions.
  • Data entry validation: Confirm routing numbers received from customers or vendors are mathematically valid before processing.
  • Debugging payment issues: Quickly determine if a failed transaction might be due to an incorrect routing number.

Limitations

  • Validates mathematical correctness only—a valid checksum doesn't guarantee the routing number is currently assigned to an active bank
  • Only works for U.S. ABA routing numbers; does not validate international bank codes (SWIFT, IBAN, etc.)
  • Cannot identify which bank a routing number belongs to

FAQ

What's the difference between ABA routing numbers and SWIFT codes? ABA routing numbers are used only within the United States for domestic transfers. SWIFT codes (also called BIC codes) are used for international wire transfers and identify banks worldwide.

Where can I find my bank's routing number? You can find your routing number on the bottom left corner of personal checks, in your online banking portal, or by contacting your bank directly. Note that some banks use different routing numbers for paper checks versus electronic transfers.

Can a routing number be valid but not exist? Yes. This tool validates the mathematical checksum, not whether the number is assigned to a real bank. A number could pass validation but not be in active use.