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Routing Number - How to Calculate

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Question: 
How do you calculate the last digit in a routing number - using the fraction in the top right corner of the check?
Answer: 

I haven't had anyone ask this in a long time! The last digit of the routing number can be figured by using the formula Rand McNally and the ABA created a long time ago. It will verify the authenticity of the sequence of the routing number itself. You don't need the fraction to determine the 9th digit. You simply take the first eight digits (which IS determined by the fraction) and multiply them by 3,7,1,3,7,1,3,7. Let me illustrate. Suppose the fraction is 27 - 2 /(over) 1040. The first four digits of the routing number at the bottom of the check is the federal reserve district, which is the bottom number of the fraction - in this case the 10th FRD. So the first four digits are 1040. (Note - if the FRD is one of the first 9 districts, there will only be three digits in that number. You'd make it four by putting a "0" in front of the first three. So a "310", for instance, would become "0310") The top number, in this illustration, is 27 - 2. The 27 tells you in what city or state this particular bank is located. The 2 tells you exactly what bank it is in the federal reserve district shown in the bottom of the fraction. The second four digits in the routing number is that particular bank number. In this case, there is only one digit... 2 ... so in order to make it four digits, we have to put three zeros in front of it. 0002. Our eight digits so far, then are 10400002 To use the formula to determine the last digit, it's easiest to put the first eight numbers in a line, one under the other. Then, to the right of each number, starting at the top, put times" (x) 3-7-1-3-7-1-3-7, one right underneath the other. Then multiply them and write your answers to the right of each.

1 x 3 = 3
0 x 7 = 0
4 x 1 = 4
0 x 3 = 0
0 x 7 = 0
0 x 1 = 0
0 x 3 = 0
2 x 7 = 14

Now add up all your answers. In this case that would be 21.

You're not done yet!

Now subtract that answer from the next highest 10. In this case that would be 30. 30 - 21 = 9.

The last digit is 9. The whole transit routing number would be 104000029. It sounds more complicated than it is! Try it on your own checks to be sure you have it right.

First published on BankersOnline.com 1/7/02

First published on 01/07/2002

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