Routing Number Checker (ABA Validator)
Free tool to validate and calculate the check digit of a US bank ABA routing number (the 9-digit code used for bank transfers). Enter 8 or 9 digits and it auto-detects the format, plus looks up the Federal Reserve District. Everything runs in your browser.
What is the routing number checker?
This free online tool validates and calculates the check digit of a 9-digit ABA routing number — the code that identifies a US bank — and also looks up its Federal Reserve District. It follows the MICR-standard mod-10 checksum, which weights digits by 3, 7, and 1.
It automatically detects the input format based on length (8 or 9 digits), so there's no mode to switch manually. If you enter a number that already includes a check digit, it validates it; if you enter the 8-digit body only, it calculates and appends the correct check digit. Note that this tool only confirms whether the format is valid — it cannot identify the actual bank name (you'll need to contact the receiving bank to confirm that).
How to use it
- Enter the routing number You can paste it with spaces or hyphens still in place.
- Check the detected format and result The detected format (with or without a check digit) and the validation or calculation result are shown.
- Check the Federal Reserve District The district name looked up from the first two digits is displayed (shown as "not applicable" if there's no matching prefix).
- Try another number Use the clear button to reset the input and check a different number.
Tips for getting more out of it
- You can paste a number that still has spaces or hyphens — they are stripped automatically before the calculation runs.
- Enter the 8-digit body without a check digit and the tool automatically fills in the correct check digit to show the full 9-digit number.
- The first two digits are the "Federal Reserve Routing Symbol." If they fall in 01–12, 21–32, or 61–72, you can look up which of the 12 Federal Reserve Districts the number belongs to.
- This tool only checks whether the format (check digit) is valid — it cannot confirm whether the bank actually exists or whether the account is active. Contact the receiving bank directly to confirm those details.
- International wire transfers to US banks sometimes ask for both a routing number and a SWIFT/BIC code. Double-check which one your payment instructions actually require.
Use cases
Double-checking before an international transfer
Verify a routing number given by a US university, real estate company, or business partner before sending a wire transfer.
Accounting and legal form review
When transcribing US bank details from an invoice or payment instruction, catch format errors immediately with the check digit.
Reference for building payment validation logic
Use it as a reference to confirm the expected behavior of a routing number validation (mod-10 checksum) implemented in a US-facing payment form.
Digitizing old checks and documents
When entering routing numbers from paper checks or old contracts into a database, use the check digit to catch OCR misreads.
Glossary
- ABA routing number
- A 9-digit code devised by the American Bankers Association in 1910 that uniquely identifies a US bank, used on checks, ACH transfers, and wire transfers.
- MICR
- Magnetic Ink Character Recognition, the standard for the characters printed along the bottom of a check. It also defines the checksum formula used for routing numbers.
- Check digit
- The final digit of a routing number, calculated from a formula to detect typos and transcription errors.
- Federal Reserve District
- One of 12 regions administered by the US central banking system (the Federal Reserve). The first two digits of a routing number identify which district a bank belongs to.
- ACH
- The Automated Clearing House network used for domestic bank-to-bank transfers in the US, such as payroll deposits and direct debits, which relies on routing numbers.
- Wire transfer
- A method of moving funds between banks immediately. Some banks use a different routing number for wire transfers than for ACH transfers.
Frequently Asked Questions
Side Note — The mysterious digits under your checkbook
The ABA routing number traces back to 1910, when the American Bankers Association devised a scheme to identify every bank in the country. Checks were the dominant payment method at the time, and sorting huge volumes of them between banks by hand required a unique number for each institution. That same number is still printed today along the bottom of a check as part of the strange-looking MICR characters (magnetic ink character recognition).
The number isn't just a random sequence — its first two digits encode geography. The United States is divided into 12 Federal Reserve Districts, numbered from Boston (1) on the East Coast to San Francisco (12) on the West Coast. Because of this structure, you can tell which Federal Reserve district a bank belongs to just by looking at the first two digits of its routing number.
The trailing check digit exists to catch simple transcription errors. Using a weighted formula of 3, 7, and 1 (defined by the MICR standard), it's designed to catch most single-digit typos and digit-swap mistakes that happen when someone copies the number by hand. It's remarkable that a system devised over a century ago is still doing exactly that job today, even as online banking and ACH transfers have become the norm.