UPC / EAN Check Digit Calculation

UPC and EAN symbologies use the Modulo 10 to calculate the check digit to be added as the last digit of the code. The calculation uses a simple process of multiplication by a factor, according with their respective position in the code.

As an example, we are going to take a product with the EAN-13 code of 789123451234x (x= check digit to be calculated). Starting from the first position on the right of the code,  a factor of 3 will be applied to that position. In the second position the factor will be 1, third position will be again 3, fourth will be again 1, then following this process 3s and 1s will be applied to their respective positions until the end of the code (left).

In a second step, the original numbers of the code will be multiplied by their respective factors in each position of the code. As a third step, the results of those multiplications will be added. The sum will be subtracted from the next multiple of 10, and the result is the check digit to be added to end of the code.