So I was trying to figure out how long ABA Routing Numbers are valid for and accidentally unearthed a whole slew of facts I never knew about the little digits identifying your bank on your checks:

ABA stands for American Bankers Association and they come up with the ABA Routing Numbers, here’s a boring and long PDF file ^{[3]} all about it.

**What do the numbers stand for?**

The first four numbers are the Federal Reserve routing symbol, which specifies which of the twelve Federal Reserve banks (including city) that the check was printed at. The next four digits specify your bank and the last digit is the checksum digit, a calculation I explain next.

**Did you know that there is a checksum validity test?**

For the non-nerds out there, a checksum just means you basically add the numbers together after doing some other mathy stuff and the result is a checksum. It’s a way to figure out if something was corrupted in the communication. To calculate the checksum for the ABA Routing Number, multiply the first digit by 3, the next by 7, the next by 1, and then repeat in that order. A valid ABA Routing Number’s checksum will be evenly divisible by 10.

So if you take Emigrant Direct’s ^{[4]} ABA Routing number of **226070319**:

**100**

**Looking for a Bank With Its Routing Number?**

Ta da! You can look it up at a Federal Reserve Financial Services website ^{[5]}. I wonder if they give better rates at ABA#: 2839-7842-5 ^{[6]}.

I’m sure there are other great ABA facts but those are some to get you started.