Film master suppliers, on-site printing equipment, and barcoding software packages will usually calculate the check digit for you. But if you really want to know how it's done, read on!

The check digit calculation (called the “modulo 10” algorithm) is the same for EAN.UCC-8, UCC-12, EAN.UCC-13, EAN.UCC-14 and the Serial Shipping Container Code (SSCC).

Note that the check digit for a UCC-12 Zero Suppressed number (known as a UPC-E barcode) is calculated using the first 11 digits of the number in its expanded form.

Let's perform the following calculation using the EAN-13 number in the barcode below:

EAN-13 barcode: 93 12345 67890 ?

? = unknown check digit

1. Starting with the first known number on the right, add all the alternative numbers working to the left. Then multiply the result by three.

0 + 8 + 6 + 4 + 2 + 3 = 23 x 3 = 69

2. Starting with second known number on the right, add all alternative numbers again working to the left.

9 + 7 + 5 + 3 + 1 + 9 = 34

3. Add the results of steps one and two.

69 + 34 = 103

4. Add the number needed to bring the total to the next multiple of ten, being 110. In this example, add 7. If the result is a multiple of ten then the check digit is 0 (not 10).

The number added to bring the total to the next multiple of ten becomes the check digit = 7

The complete barcode number in the example above will be: 93 12345 67890 7.

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