ISSN - Code Format

Code Format

The format of the ISSN is an eight digit number, divided by a hyphen into two four-digit numbers. The last digit, which may be 0–9 or an X, is a check digit. The ISSN of the journal Hearing Research, for example, is 0378-5955, the check digit is 5.

To calculate the check digit, the following algorithm may be used:

Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right — that is, 8, 7, 6, 5, 4, 3, and 2, respectively:

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The modulus 11 of this sum is then calculated: divide the sum by 11 and determine the remainder.

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If there is no remainder the check digit is 0, otherwise the remainder value is subtracted from 11 to give the check digit:

5 is the check digit.

An upper case X in the check digit position indicates a check digit of 10.

To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right (if the check digit is X, then add 10 to the sum). The modulus 11 of the sum must be 0.