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Routing number validator
Check whether a 9-digit US ABA routing number is valid using its weighted checksum. Confirms internal consistency — not whether the bank is active.
Input
Routing number check
—Enter a 9-digit ABA routing number to verify its checksum.
A free routing number validator that checks a 9-digit US ABA bank routing number using the standard weighted checksum. Enter any routing number and get an instant pass/fail — the tool confirms internal consistency but cannot verify whether a bank is active or registered. Runs entirely in your browser.
How to validate a routing number
- Type or paste the 9-digit routing number into the input field.
- The tool applies the ABA 3-7-1 weighted checksum formula to all nine digits.
- It checks that the result is divisible by 10.
- Result shows valid checksum or invalid, with the specific failure reason.
The ABA 3-7-1 weighted checksum explained
The ABA routing number checksum multiplies each digit by a repeating weight sequence: 3, 7, 1, 3, 7, 1, 3, 7, 1 (for positions 1 through 9). The nine products are summed, and a valid routing number's total is exactly divisible by 10. This simple scheme catches most single-digit entry errors and all transposition errors between adjacent digits — which are the most common input mistakes. It was designed in the early 20th century and remains the only structural check used by the US banking system for routing numbers.
What checksum validation does not confirm
- Whether the routing number belongs to a real, currently active financial institution.
- Whether the bank accepts ACH, wires, or other specific transfer types.
- Whether the account number paired with this routing number is valid.
- Routing numbers change when banks merge; a valid checksum may still be for a closed or merged bank.
Frequently asked questions
What does routing number validation check?
It verifies the 9-digit number passes the ABA 3-7-1 weighted checksum — confirming it is internally consistent. It does not confirm the number is in the Federal Reserve's active routing directory.
How do I know if a routing number belongs to a real bank?
After confirming the checksum, look up the number in the Federal Reserve's free FedACH directory (fedpaymentsimprovement.org) or your bank's official website. Those sources confirm active registration.
Why does routing number validation matter?
The ABA checksum catches about 90% of single-digit transcription errors before a payment is submitted, preventing failed ACH transfers and wire returns that can take days to reverse.
Does this tool store the routing numbers I enter?
No. Validation runs entirely in your browser. No data is sent to any server or third party.