GTIN, UPC & EAN Checksum Validator

Every GTIN, UPC, EAN and ISBN-13 number ends in a check digit, a single number calculated from all the digits before it using a fixed formula. If a digit is mistyped, transposed or dropped when a product listing or feed is built by hand, the check digit no longer matches and the code is invalid, which is exactly what this tool catches before a bad number reaches a live feed.

How the check digit is calculated

The GS1 standard used for GTIN, UPC and EAN numbers calculates the check digit with a weighted sum. Starting from the digit immediately to the left of the check digit and moving left, each digit is multiplied by 3, then 1, alternating all the way to the first digit. The products are added together, and the check digit is whatever number, when added to that sum, brings the total to the next multiple of 10. ISBN-13 numbers use this same EAN-13 structure and always start with the prefix 978 or 979.

Why this matters for product feeds

Google Merchant Center, Amazon and most marketplaces validate GTIN format before accepting a listing, and an invalid check digit is one of the most common reasons a product gets rejected or flagged in a feed. Catching the error here, before uploading a feed of hundreds or thousands of SKUs, is faster than waiting for the marketplace to reject individual listings one at a time.

What to do with an invalid code

An invalid result almost always means a digit was mistyped, transposed, or the wrong number of digits was entered. Go back to the original product packaging, the manufacturer's data sheet, or your GS1 registration and re-enter the exact digits printed there. If the barcode itself is genuinely invalid, it needs to be corrected with your GS1 member organization or the manufacturer, not just re-typed.