How to use this calculator
Start with the deterministic fixture values already shown, then replace each input with measurements from your job. Use consistent units and review the highlighted assumptions before using the result in purchasing or production.
Formula and method
Starting at the rightmost body digit, multiply alternating digits by 3 and 1, sum the products, and choose the digit that brings the sum to the next multiple of ten: (10 − (sum mod 10)) mod 10.
Worked example
For GTIN-13 body 400638133393, the alternating weighted sum is 89, so the check digit is 1 and the complete identifier is 4006381333931.
How to interpret the result
A valid check digit catches many transcription errors. It does not prove that an identifier was properly licensed, allocated or assigned.
Limitations
Only the numeric lengths listed are accepted. Application identifiers, element strings, Digital Link syntax and company-prefix allocation are outside this calculator.
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