The ABA routing number has a weighted checksum — digits multiplied by 3, 7 and 1 in rotation, summing to a multiple of ten. Getting it right means your ACH form validates the number and moves on to whatever you actually wanted to test.
What you can control
- US routing numbers carry a correct 3-7-1 weighted checksum.
- Four regional formats: ABA, UK sort code, Canadian transit-and-institution, Australian BSB.
- Account number length is adjustable from 6 to 17 digits, covering the range real institutions use.
- Account type and bank name round out the record for seeding a payments table.
What this is not
Routing numbers here pass the checksum but are not registered with any clearing house. An ACH transfer using one will be rejected by the receiving bank.
Questions
Do these routing numbers belong to real banks?
No. They satisfy the checksum without being registered in the Federal Reserve's routing directory, so a lookup will find nothing.
Why do account numbers vary in length?
Because banks choose their own, anywhere from six to seventeen digits. A form that hard-codes a length will reject legitimate customers.
What is a BSB?
Bank-State-Branch — the six-digit Australian equivalent of a routing number, written as three digits, a hyphen, then three more.