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GTIN Check Digit Calculator
Enter your GTIN digits and see exactly how the check digit is calculated, step by step.
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How the GS1 check digit algorithm works
Every GTIN ends with a single check digit. This digit catches scanning and data entry errors by validating the rest of the number. The same algorithm is used across all GTIN formats (GTIN-8, GTIN-12, GTIN-13, GTIN-14), UPC, EAN, and ISBN-13.
The algorithm
- Pad the digits. Zero-pad to 13 positions (the standard GTIN-14 payload length).
- Assign weights. Starting from the rightmost digit, alternate between multiplying by 3 and 1. The rightmost payload digit always gets x3.
- Multiply and sum. Multiply each digit by its weight, then add all the products together.
- Calculate the remainder. Divide the sum by 10 and take the remainder.
- Subtract from 10. The check digit is (10 - remainder) mod 10. If the remainder is 0, the check digit is 0.
Why check digits matter
A single transposed or mistyped digit would cause a product to scan as a completely different item. The check digit catches these errors at the point of sale, in warehouse systems, and anywhere GTINs are manually entered. The x3/x1 weighting pattern specifically detects single-digit errors and most adjacent transpositions.