My barcode is invalid - how do I fix the check digit?

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Check a barcode

Barcode (UPC / EAN / GTIN)

8, 12, 13 or 14 digits. Spaces and hyphens are ignored.

Enter a barcode above to check its check digit.

You typed a barcode into Shopify, and now a scanner rejects it or LabelCraft flags it as invalid. The most common cause is a single wrong digit: the last digit of an EAN-13, UPC-A or ITF-14 is a check digit computed from all the others, so a single typo anywhere breaks the match and the whole code fails. The good news is that one kind of failure has a mechanical fix.

What the check digit is

The final digit of an EAN-13, UPC-A or ITF-14 is not part of the product identity - it is a GTIN check digit, calculated from the other digits with the GS1 mod-10 algorithm. A scanner recomputes it on read; if the value you stored does not match what the other digits imply, the scanner rejects the code outright. Mistype any digit and that match breaks.

The one-digit fix

When a value has the right length - 8, 12, 13 or 14 digits - but the check digit is wrong, the repair is mechanical: recompute the last digit from the rest. Take 4006381333930. Its 13 digits are the correct length for an EAN-13, but the final 0 does not match the mod-10 result of the first twelve. Recompute it and you get 4006381333931 - the same product number with a valid check digit. LabelCraft suggests this corrected value for you automatically.

When recomputing is the WRONG fix

Recomputing only helps when the length is already right. A different, very common problem looks similar but needs the opposite treatment: a dropped leading zero. A 12-digit UPC-A pasted from Excel or Google Sheets often loses its leading zero and arrives as 11 digits. Recomputing a check digit on those 11 digits would mint a brand-new, valid-looking number that points at the wrong product. So LabelCraft does NOT offer the check-digit fix for an 11-digit value - you retype the real 12-digit number instead. See the leading-zero guide for that case.

One honest caveat

Recomputing the check digit cures a typo in the check digit itself. But if the digit you mistyped was a data digit - one of the product digits - then recomputing simply makes the wrong number valid, and the now-scannable code points at the wrong item. The fix makes a code legal, not necessarily correct. Always confirm the full number against your supplier or the GS1 source before you print a whole roll.

How LabelCraft handles it

LabelCraft audits every barcode before it prints. For a right-length value with a bad check digit, it shows the recomputed value behind a Fix button - one click turns 4006381333930 into 4006381333931. For a dropped leading zero it stays silent and offers no check-digit fix, because the right repair there is a different number, not a recomputed digit. The app would rather flag a code than quietly print one that scans wrong - the same never-silent rule that runs through everything it does.

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More guides: how the GTIN check digit works, the dropped leading zero in Excel, why a barcode won't scan - or contact LabelCraft support.