Add-on symbols (barcodes) can also be used with EAN-13, UPC-A, and UPC-E barcodes in some applications. Add-on symbols can contain additional 2 or 5 digits and are usually placed to the right of the main barcode.

The additional characters are the left margin character and the bar code character separated by the delineator character. Additional characters do not include right margin characters and check digits. For barcode self-checking, the numbers are encoded with variable parity based on special rules.

"UPC-E" barcode with "02" add-on symbol

"EAN-13" barcode with "00321" add-on symbol