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ABA Routing Number Validator

Enter a 9-digit ABA routing number to validate its checksum.

Result

9 digits
30
Yes

How it is calculated

Type a routing number; every character that is not a digit (spaces, hyphens) is removed first, so 0210-00021 and 021000021 are treated the same. If exactly nine digits remain, each digit is multiplied by a repeating weight pattern 3, 7, 1, 3, 7, 1, 3, 7, 1 and the products are added: sum = 3(d1+d4+d7) + 7(d2+d5+d8) + 1(d3+d6+d9). The number passes when sum mod 10 = 0. The tool shows the digit count, the sum and a Valid answer: Yes when the checksum passes and No when it fails. With any other number of digits, the sum is shown as a dash and the answer is No. A text with no digits at all gives no result. This tests the check digit only: it does not look the number up, so a passing number may still not belong to any bank, and even a string of nine zeros passes.

Worked example

Check 021000021. The digits are 0, 2, 1, 0, 0, 0, 0, 2, 1. Multiply by the weights 3, 7, 1, 3, 7, 1, 3, 7, 1: 0×3 + 2×7 + 1×1 + 0×3 + 0×7 + 0×1 + 0×3 + 2×7 + 1×1 = 0 + 14 + 1 + 0 + 0 + 0 + 0 + 14 + 1 = 30. Since 30 divides evenly by 10, the number passes: the tool reports 9 digits, a checksum of 30 and a valid answer of Yes. Changing the last digit to 2 makes the sum 31 and the answer No.

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Common mistakes

  • Reading Valid = Yes as confirmation that the bank exists. The check only catches typing errors; the number must still be looked up in the official register of routing numbers.
  • Entering an account number, a SWIFT/BIC code or an IBAN. Only the 9-digit ABA routing number is meant, and a longer string just reports the wrong length.
  • Dropping the leading zero. Routing numbers often start with 0, and an 8-digit entry fails on length before any checksum is calculated.
  • Expecting a character-by-character error report. When the sum is not a multiple of 10 the tool says only that it fails, not which digit is wrong.
  • Using it for wire details outside the U.S. Routing numbers of this form belong to the U.S. system; other countries use different formats and check rules.

About this calculator

A U.S. ABA routing number (also called an RTN) is a 9-digit code identifying the financial institution on a check or ACH transfer, where the ninth digit is a checksum computed from the first eight: 3(d1+d4+d7) + 7(d2+d5+d8) + (d3+d6+d9) must be evenly divisible by 10 for the number to be structurally valid. The formula was designed by the American Bankers Association in 1910 to let clearinghouses catch transcription errors before a payment is misrouted.

This validator runs the checksum on a 9-digit number you enter and reports whether it passes, without confirming the routing number is actually assigned to a real bank (that requires a lookup against the Fed's registry). Developers building payment or ACH integrations, and bookkeepers double-checking a check use it as a fast first-pass sanity check before submitting a transaction or entering banking details into a form.

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Comments (1)

  • Editorial team

    A passing result does not catch every slip. Swapping two neighbouring digits that differ by exactly 5, such as a 0 and a 5, leaves the checksum unchanged. Using made-up test numbers, 100000052 and 100000502 both pass here. So for a real payment, compare the number digit by digit with the printed source and confirm which routing number your bank uses, since some list separate ones for ACH and wires. What are you validating the number for?

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