How does the GTIN check digit work?
The final digit of a GTIN helps detect many common input errors.
Why use a check digit?
Long numbers are easy to mistype. The check digit provides a mathematical integrity check without requiring product data.
The principle
Starting from the right, the digits before the check digit are weighted alternately by 3 and 1. The results are added and the check digit completes the sum to the next multiple of 10.
Simple example
If the weighted sum is 67, the missing value up to 70 is 3, so the check digit is 3. If the sum is already a multiple of 10, the check digit is 0.
What it does not prove
A valid check digit confirms only the structure. It does not prove that a product exists or that descriptive data is correct.