How to use the aba routing number validator
- Type or paste the nine digit routing numbers, one on each line. Spaces and hyphens are ignored.
- Add an eight digit number on its own line if you want the missing last digit worked out.
- Read the result for each line: whether the check digit works, the weighted sum, and the digit it would need.
- Copy the table or download the CSV to keep a record of what you checked.
Formula
sum = 3 x (d1 + d4 + d7) + 7 x (d2 + d5 + d8) + 1 x (d3 + d6 + d9)
valid when sum mod 10 = 0
last digit = (10 - (3 d1 + 7 d2 + d3 + 3 d4 + 7 d5 + d6 + 3 d7 + 7 d8) mod 10) mod 10
The digits are weighted 3, 7 and 1 in a repeating pattern across all nine positions. The ninth digit is chosen so that the total is a multiple of 10.
Checking 021000021
The nine digits are 0, 2, 1, 0, 0, 0, 0, 2 and 1. Multiplying by 3, 7, 1, 3, 7, 1, 3, 7, 1 gives 0, 14, 1, 0, 0, 0, 0, 14 and 1. They add up to 30, which is a multiple of 10, so the check digit works.
Change the last digit to 2 and the sum becomes 31, which fails. For the eight digits 02100002 the page adds the check digit that brings the sum to 30, so the full number is 021000021. Every one of the 81 ways to change a single digit of 021000021 makes the test fail.
What the check digit does and does not prove
The weights 3, 7 and 1 catch every single wrong digit and most swaps of neighboring digits. That makes the test good at catching typing mistakes before a payment is sent.
It cannot tell you whether a bank uses the number. Many nine digit strings pass the test and belong to nobody. Confirm the number with the bank or from a recent statement before sending money.
The prefix range column
The first two digits are shown with the range they fall in, such as the primary range 01 to 12. This is only a label for the digits. It does not say which bank or region the number belongs to, and it does not mean the number is assigned or active.
Use the Check Digit Validator for card, ISBN and product numbers, and the IBAN Structure Checker and Builder for international accounts.
Assumptions and limits
- Only the United States nine digit format is tested. Canadian, UK and other bank codes use different rules.
- The tool checks the arithmetic of the digits and nothing else. It does not look anything up and sends nothing anywhere.
- Spaces and hyphens are removed before testing. Letters and other characters are rejected.
- Up to 200 lines are read at once.
- The prefix ranges are descriptive labels for the first two digits only.
Frequently asked questions
Why is the weighting 3, 7, 1?
Those weights are the standard pattern for this kind of number. Because 3, 7 and 1 do not share a factor with 10, any single wrong digit changes the sum by an amount that is not a multiple of 10, so it is always caught.
Can a routing number pass and still be wrong?
Yes. About one in ten random nine digit strings passes by chance. A pass means the digits are consistent. It does not mean the number was ever issued, so always confirm with the bank.
What if my number has only eight digits?
Put it on its own line. The page treats eight digits as the start of a routing number and works out the ninth digit that makes the weighted sum a multiple of 10.
Does this work for wire transfers?
The same nine digit check applies to the numbers used for domestic transfers in the United States. International wires use other codes, so ask the receiving bank which numbers to use.