GTIN, UPC & EAN Check Digit Calculator

The algorithm

1. Pad the digits. Zero-pad to 13 positions (the standard GTIN-14 payload length).
2. Assign weights. Starting from the rightmost digit, alternate between multiplying by 3 and 1. The rightmost payload digit always gets x3.
3. Multiply and sum. Multiply each digit by its weight, then add all the products together.
4. Calculate the remainder. Divide the sum by 10 and take the remainder.
5. Subtract from 10. The check digit is (10 - remainder) mod 10. If the remainder is 0, the check digit is 0.

Worked example: the UPC-A 01234567890

Eleven payload digits, weighted from the right. The rightmost one takes x3, and the weights alternate from there.

The products sum to 85. The next multiple of ten is 90, so the check digit is 5 and the complete UPC-A is 012345678905. Change any single digit in that number and the sum moves off the multiple of ten, which is exactly the property that makes the check digit useful.

UPC, EAN, and GTIN are the same calculation

These names describe how wide the number is printed, not how it is built. A UPC-A is a GTIN-12, an EAN-13 is a GTIN-13, and an EAN-8 is a GTIN-8. All of them run through the algorithm above unchanged, so there is no separate “UPC check digit formula” to look up. Enter every digit except the last one and the calculator returns the digit that completes it.

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.