ABA Routing Number Validator

ABA routing number: the 9-digit US bank code with a 3-7-1 checksum

The ABA routing number (RTN — Routing Transit Number) is the 9-digit code that identifies a US financial institution for cheques, ACH and wire transfers. Introduced by the American Bankers Association in 1910, it carries a real checksum, so this tool can confirm the digits are internally consistent — the example 011000015 is a Federal Reserve Bank of New York routing number.

The check is a weighted sum: apply weights 3, 7, 1 repeating across the nine digits; the total must be a multiple of 10. That single rule catches most single-digit and transposition typos before a payment is sent.

Reading the number

• Digits 1–2: the Federal Reserve district / processing region (e.g. 01 Boston, 02 New York, 12 San Francisco).
• Digits 3–4: the Fed office and the bank's identity within it.
• Digits 5–8: the specific institution.
• Digit 9: the 3-7-1 check digit.

The 3-7-1 checksum, step by step

• Weights: 3 7 1 3 7 1 3 7 1 across the nine digits.
• Sum: multiply each digit by its weight and add.
• Rule: the sum is valid only if it's divisible by 10.
• Valid range: the first two digits must fall in the assigned Fed ranges (00–12, 21–32, 61–72, 80).

Common pitfalls

• Checksum ≠ active: a number can pass the 3-7-1 test yet not be a live, assigned RTN.
• Wire vs ACH routing: a bank may publish different routing numbers for ACH and wires — don't assume one fits all.
• Leading zeros: store as a 9-character string; many RTNs start with 0.
• RTN ≠ account: the routing number names the bank; the account number names the account.

FAQ

How is the ABA checksum computed? Weights 3,7,1 repeating; the weighted sum of all nine digits must be divisible by 10.

Why do I have two routing numbers? Banks often use separate RTNs for ACH (direct deposit) and for domestic wires.

Is a valid checksum enough to send money? No — it only proves the digits are consistent; the receiving bank/account must still exist.