Routing Number Validator — ABA Checksum + Federal Reserve Symbol

Real-world use cases

• Catch a typo before setting up a direct deposit

  You are filling out a payroll or ACH form and typed the routing number off a check. Drop it in here first. If a digit is wrong the checksum fails immediately, and a single transposed pair almost always trips the 3-7-1 formula. Better to see a red verdict here than to have a paycheck bounce back days later because the routing number was one digit off.

• Validate a batch source field while writing payment code

  Building an ACH integration or a check-import parser? Use the exported isValidRoutingNumber helper as a quick format gate before you call the bank or a paid verification API. Paste sample routing numbers here to confirm your test fixtures actually pass the ABA checksum, so your unit tests assert against numbers that are structurally real rather than random 9-digit strings.

• Figure out which Federal Reserve region a number belongs to

  You have a routing number and want to know roughly where it clears. The first two digits give you the Federal Reserve routing symbol, so a number starting 11 maps to District 11 Dallas and one starting 02 to District 2 New York. The tool surfaces that region from the public range table, which is handy for sanity-checking that a vendor gave you a domestic US routing number and not something malformed.

• Teach how check encoding and the ABA checksum work

  Explaining MICR lines, ACH or the ABA algorithm to a class or a new teammate? Type a known routing number and walk through why the checksum lands on a multiple of 10, then change one digit and watch the verdict flip to invalid. The shareable URL reopens the exact example, so you can send a working link instead of a screenshot.

Common pitfalls

• Treating a passing checksum as proof the bank exists. The 3-7-1 formula only checks structure. A made-up number like a well-chosen 9-digit string can pass and still belong to no real institution, so never wire money on the strength of a green verdict alone.

• Mixing up the routing number with the account number. The routing number is the 9-digit group on the far left of the bottom of a check; the account number is the group next to it. Feeding an account number in here gives a meaningless result because account numbers have no fixed length or ABA checksum.

• Entering more or fewer than 9 digits. A US routing number is exactly 9 digits. International bank codes such as SWIFT/BIC or IBAN have completely different formats and lengths, so they will never pass this checker. Strip spaces and confirm the count reads 9 of 9 before trusting the result.

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