EAN-13 Check Digit Calculator

About this calculator

This calculator applies the official EAN-13 / GS1 checksum algorithm: starting from the left, multiply each of the first 12 digits alternately by 1 and 3 (odd positions ×1, even positions ×3), sum the results, and take the check digit as the number that rounds that sum up to the next multiple of 10 — formally, (10 − (sum mod 10)) mod 10.

Every retail barcode — EAN-13, UPC-A (its 12-digit North American sibling), and ISBN-13 — uses this same weighted mod-10 scheme, which is why a single-digit typo or a smudged scanner read almost always gets caught before a wrong price rings up. Retailers, packaging designers, and inventory systems use it to generate valid new codes and to verify that an existing barcode wasn't mistyped or corrupted.