Using the above EAN Barcode reading 50 12345 12345(5), which is made up of 12 digits plus a final check digit which in this case is the number 5.
The calculation is:
Step 1. Start by adding the first digit (left to right method in this case 5) with each alternate digit i.e. in this case 5,1,3,5,2,4, = 20 (Red Group)
Step 2. Now add the unused digits digits in this case 0,2,4,1,3,5, = 15 and times the total by 3 = 45 (Blue Group)
Step 3 Add the two totals in Step 1 and Step 2 together i.e. 20 + 45 = 65.
Step 4 The check digit is the smallest number when added to the result that produces a multiple of 10.
So for this Barcode the check digit is 5 i.e. 65 + 5 = 70
Now you can make sure you supply the correct number to your Graphic Designer or simply impress your friends at the pub.