United States ABA routing number validator
How the ABA routing number format works
- Format
- 9 digits
- Example
- 021000021
Things to watch for
- 9 digits with a weighted mod-10 check digit
- Checksum only — does not confirm the bank or account exists
- Some banks use different routing numbers for wires vs. ACH
^[0-9]{9}$A US ABA routing number is the 9-digit code that identifies which financial institution a check, direct deposit, or ACH transfer is meant to reach, printed along the bottom-left of every personal check and used anywhere you set up payroll, autopay, or a wire transfer. The American Bankers Association introduced the system in 1910, and every US bank or credit union that clears paper checks or electronic payments has been assigned one since.
The 9 digits aren’t arbitrary — the last one is a check digit generated from the other 8 using a fixed weighting pattern (3, 7, 1, repeating), which is what lets a computer catch a mistyped or transposed digit before a payment goes to the wrong institution. Getting even one digit wrong when entering a routing number for payroll or a bill payment can misdirect the transfer or bounce it entirely, so it’s worth validating the number before it’s submitted anywhere.
How this validator works
This tool checks that the input is exactly 9 digits and then runs the real ABA mod-10 formula — weighting each digit 3, 7, or 1 in sequence and confirming the weighted sum is a multiple of 10 — entirely in your browser. Nothing is sent to a server, and there’s no signup.
What a pass doesn’t tell you
A pass means the 9 digits are internally consistent with how the ABA generates valid routing numbers — it doesn’t confirm the number is currently assigned to an active bank, or that the account you’re pairing it with exists. It also won’t tell you whether a bank uses a separate routing number for wires versus ACH transfers, which is common among larger institutions.
Scope: this page and tool cover routing number format and checksum validation only — not bank lookup, account verification, or wire-versus-ACH routing differences.
Content last reviewed 2026-07-07.
ABA routing number FAQ
Where do I find my bank's routing number?
On a personal check, it's the first 9-digit number printed along the bottom-left edge, to the left of your account number. It's also usually listed on your bank's website or mobile app under account or direct-deposit details.
Does a valid checksum mean the routing number belongs to a real bank?
No. This tool only confirms the 9 digits pass the ABA mod-10 check-digit formula used to generate every valid routing number — it doesn't look the number up against a real institution. A routing number can pass the checksum and still not correspond to any bank currently using it.
Why does my bank seem to have more than one routing number?
Many banks, especially larger ones, use different routing numbers for different purposes — one for direct deposit and ACH transfers, another for wire transfers. Both can be valid, so check which one your sender or payroll department actually needs.