How is an ABA routing number checksum calculated?

Multiply the nine digits by the repeating weights 3, 7, 1, 3, 7, 1, 3, 7, 1, sum the products, and the number is valid if that sum is divisible by 10. This is the standard ABA modulus-10 check.

What do the first digits of a routing number mean?

The first two digits indicate the Federal Reserve district (01–12) or a special-purpose range (00 for the US government, 21–32 for thrifts, 61–72 for electronic transactions, 80 for traveler's checks). The tool decodes this range for you.

Can the tool identify which bank it is?

It identifies major institutions whose routing prefixes are in the bundled directory. The full Federal Reserve routing file lists thousands of numbers, so an unmatched valid number is normal — the checksum still confirms it is well-formed.

Is a valid checksum enough to send a payment?

No. A valid checksum only proves the number is structurally correct. Confirm the routing number with the receiving bank or the official Federal Reserve E-Payments Routing Directory before initiating an ACH or wire transfer.

Are ACH and wire routing numbers the same?

Not always. A bank may publish different routing numbers for ACH transfers, domestic wires, and check processing. All pass the same checksum, but use the specific number the bank designates for your transfer type.

US ABA Routing Number Validator (Bank Identified)

A US ABA routing number (also called a routing transit number, RTN) is the 9-digit code that identifies the financial institution in ACH transfers, wires, and check processing. It carries a built-in checksum so transposed digits are caught immediately. This validator runs the official 3-7-1 weighted modulus-10 check, decodes the Federal Reserve district, and names major institutions from a bundled directory.

How it works

The American Bankers Association defines a weighted check:

Take the nine digits d1 d2 d3 d4 d5 d6 d7 d8 d9.
Multiply by the repeating weights 3, 7, 1, 3, 7, 1, 3, 7, 1.
Sum the nine products.
The number is valid if the sum is divisible by 10 (checksum mod 10 = 0).

The first two digits encode the issuing Federal Reserve district or a special range (e.g. 00 = US government, 01–12 = the twelve Fed districts, 21–32 = thrift institutions). The tool decodes that range and looks up the institution prefix in its bundled list.

Example

For routing number 021000021:

(0×3)+(2×7)+(1×1)+(0×3)+(0×7)+(0×1)+(0×3)+(2×7)+(1×1) = 30

30 is divisible by 10, so the checksum passes; the 02 prefix places it in the New York Federal Reserve district, and the directory identifies it as JPMorgan Chase.

Notes

A valid checksum means the number is well-formed, not that it is the correct routing number for a given account or transfer type. Always confirm against the bank or the Federal Reserve E-Payments Routing Directory. Everything runs locally in your browser.