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What is a Check Digit?

A "check digit" is a number that forms the final digit in some GS1 identification keys including product identifiers (GTINs) and Global Location Numbers (GLNs).

The check digit is calculated using a formula called the Modulo 10 algorithm which you can see below.

Here is an example of it applied to an 18-digit identifier.

The check digit is necessary as it tells the scanner that the identifier being used was correctly calculated.

The good news is that you don't need to calculate the check digit yourself. If you use Barcode Manager for your products, the system calculates all your numbers for you. If you are manually assigning your barcodes, you will need to use either your own software or our Check Digit Calculator to find the check digit.

You can find out more about the Check Digit Calculator in our article What is the Check Digit Calculator?