EAN13 Check Digit Calculation
Symbol above depicts EAN13 bar code. Last 13th digit in this barcode is the check digit (the "5").
As you see in EAN13 the check digit, a single checksum digit. The check digit is computed modulo 10, where the weights in the checksum calculation alternate 1 and 3. In particular, since the weights are relatively prime to 10 the EAN system will detect all single digit errors. But since the difference of consecutive weights is even, the EAN system does not detect all adjacent transposition errors.
Howto calculate EAN13 Check Digit

To calculate EAN13 check digit you can use interactive tool o this website: Check Digit Calculator

Make Sure you enter all thirteen digits (you can use the 0 for the last one that you do not know  the tool will correct you if necessary).

Example of EAN13 that is correct: Correct Check Digit

Example of EAN13 that is incorrect: Incorrect Check Digit