UDI / GTIN check digit

FAQ

What check digit does GS1 use for GTIN / UDI-DI?

GS1 GTINs (GTIN-8, GTIN-12, GTIN-13, GTIN-14) use a modulo-10 check digit computed from the preceding digits with alternating weights of 3 and 1 from the right. Many FDA Unique Device Identifier device identifiers (UDI-DI) that use GS1 encode a GTIN, so the same check digit applies.

What do FDA’s UDI rules require at a high level?

FDA’s unique device identification system is set out in 21 CFR Part 830, with related labeling provisions such as 21 CFR 801.20. Devices generally must bear a UDI on the label and packages unless an exception or alternative applies, and device identifiers are submitted to GUDID. This tool only checks the GS1 arithmetic — not issuing-agency assignment, packaging hierarchy or GUDID content.

Which lengths does this validator accept?

Eight, twelve, thirteen or fourteen digits (GTIN-8 / GTIN-12 / GTIN-13 / GTIN-14). Spaces, parentheses and Application Identifier wrappers are stripped before the check. Other issuing agencies or non-GTIN formats are out of scope.

Does a valid check digit mean the UDI is FDA-listed?

No. A matching check digit only means the digit string is internally consistent under GS1 rules. Issuing-agency registration, correct packaging level, production identifiers and GUDID submission are separate obligations.

How do I compute a missing check digit?

Enter the body digits plus a placeholder last digit (or an incorrect one). When the check fails, the result shows the expected check digit and a suggested full string. Confirm against your issuing-agency allocator before printing labels.

Should I also parse Application Identifiers?

Yes when the barcode carries AI elements such as (01) GTIN, (17) expiry, (10) lot and (21) serial. Use the GS1 UDI AI parser for the human-readable AI string; use this page for the GTIN check digit itself.