An EAN-13 barcode (originally European Article Number, but now renamed International Article Number) is a 13 digit (12 + check digit) barcoding standard.*
The EAN-13 barcodes are used worldwide for marking products often sold at retail point of sale. The numbers encoded in EAN-13 barcodes are product identification numbers, which are also called Japanese Article Number (JAN) in Japan. All the numbers encoded are known as Global Trade Item Numbers (GTIN).*

EAN-13 codes may also be used to encode RCN-13s (13-digit Restricted Circulation Numbers) used to identify own-brand products sold only in their stores. These are formatted as 20xxxxxxxxxxx to 29xxxxxxxxxxx.

Labeljoy requires you to enter 12 digits to generate the barcode.
Enter the 12 digits in the text box.
The 13th digit (or check digit) is automatically calculated.

EAN-13 symbol

EAN-13 barcodes can also encode 2 or 5 additional digits. Enter the additional digits in the right text box.

EAN-13 with a 2-digit add-on EAN-13 with a 5-digit add-on

Text concatenation:
When an EAN-13 barcode element is generated by concatenating fields or counters, the following rules apply:
- For the main barcode, only the first 12 digits found will be considered.
- For the add on, a dash (-) separator is required followed by 2 or 5 digits.
When a value not complying with the above rules is found, the barcode is not displayed.

The human readable text can also be shown above the symbol or hidden according to the setting specified in the Text combo box.

EAN-13 with text above the symbol EAN-13 with hidden text

* From wikipedia.