United States Banking Institution Account Number Regular Expression?

Question

I have been tasked to "verify" the length of a U.S. Banking Institution ACCOUNT NUMBER for a web app I'm developing. I cannot find anything through SOF, Google, Fed reserve etc that outlines an account number standard length that we have in the United States. For the record I believe this is futile.

If someone could point me to any official documentation on the web, or has an example regular expression, or knows if there is a standard that exists, I would appreciate it greatly.

ADDED:

What would interest me even more since the response is overwhelming that their is no standard....has anyone ever run into a bank account number that is not completely "numeric"\

ADDED:

Thanks to everyone and their responses. Due to having no standard in the US, we are not going to enforce a length check, and we are going to store the number as a varchar due to the fact that it may be possible that a bank may assign alpha characters in their account numbers. Seems 99.999999% unrealistic in our view, but no standard means we will accept alpha characters and run the check on the account number to verify if it works or not. Thanks again all!

Answer 1

There is no standard for US banks' account numbers.

IBAN is not used in the US.

There is a limit for ACH transactions (4-17 digits), but not all transactions have to be ACH.

And yes, the US banking system is antiquated.

I'm looking at a DW (Data Warehouse) of 38 different systems at a bank and the length of account varies widely depending on the product. Several of the systems have alphabetic characters in the account numbers. This is probably irrelevant since they are special types of customer accounts like brokerage accounts and other things which aren't accessible through ACH - you need to specify what kind of account you're interested in. If you restrict yourself to accounts which you can get to through ACH, you can simply restrict to numeric digits.

You can get a lot more information about ACH at: http://www.nacha.org/

Answer 2

Good luck with that, because you can't.

Banks are free to use just about anything as an account number. I think the only validation you can do is whether or not they're numeric (as they all are).

The most common length for bank account numbers is 9, 12, or 10 digits. Although they range from 4 to 17 digits long. I have a large database of valid numbers and there's no pattern that I can see to the "account number".

A "routing number" defines the bank (pretty much) but even within a particular routing number, the account numbers can be of different lengths.

This is why payroll services often require an extra day (or two) before initiating Direct Deposit in order to "prenote" the account (validate it by performing a no-op ACH transaction) because you really can't verify it otherwise.