The ABA Routing Number Check Digit Calculator is a very simple and easy to use utility to calculate the check digit on an 8 digit ABA routing number and validate the check digit on a 9 digit routing number.

Download the ABA Routing Number Check Digit Calculator (240k)

Installation:
1) Run the installer.

How to use:
1) Type in the 8 digit routing number and press enter. This will display the check digit.

2) Type in the 9 digit routing number and press enter. This will display whether or not it the check digit is correct.

Other stuff:
Download the source code (written using Borland Delphi 6)
How to calculate ABA Routing Numbers