Using Excel Barcode Add-in, you can provide EAN/UPC code without last checksum digit or with it. The Excel barcode freeware will always re-calculate the check digit based your input code, and generate the check digit for you.
The following example shows that the EAN-13 barcode on Excel cell B3 is encoding the cell A3 value, which includes 12 digits without the last check sum digit. The Excel Barcode Add-in will automatically calcuate the trailing checksum digit.