Barcode Check Digit Calculator

Free barcode check digit calculator for UPC-A and EAN-13. Enter your data digits and get the correct check digit and full barcode number instantly.

Barcode Check Digit Calculator

Enter the 11 (UPC-A) or 12 (EAN-13) data digits to get the correct check digit. Runs entirely in your browser.

By Tibeau De Grauwe, FounderUpdated September 2026

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Non-digit characters are ignored. 11 digits entered — looks like UPC-A data.

Check digit

2

Full number: 036000291452

How the check digit is calculated

Starting from the data digit immediately to the left of where the check digit goes, and moving left, multiply digits alternately by 3 and by 1 (first digit ×3, next ×1, next ×3, and so on). Sum all the weighted values, then the check digit is whatever single digit brings that sum up to the next multiple of 10 — formally, (10 − (sum mod 10)) mod 10.

UPC-A and EAN-13 use the identical algorithm; EAN-13 just has one additional data digit ahead of the same alternating 3/1 weighting pattern. This is also the same underlying check-digit method used across the wider GS1 GTIN numbering system see the GS1 barcode standards guide for how the rest of a GTIN is structured, or the barcode generator to turn a validated number into a scannable image.

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Frequently asked questions

How is a UPC-A or EAN-13 check digit calculated?
Starting from the digit immediately to the left of the check digit and moving left, multiply digits by 3 and 1 alternately (first digit ×3, next ×1, and so on), sum the results, and the check digit is whatever number brings that sum up to the next multiple of 10.
Does the same algorithm work for UPC-A and EAN-13?
Yes. UPC-A (12 digits total, 11 data digits) and EAN-13 (13 digits total, 12 data digits) use the identical mod-10 weighting algorithm — EAN-13 simply has one more data digit.
Why does my barcode generator reject a number with a valid-looking check digit?
The most common cause is a length mismatch (UPC-A needs exactly 12 digits total, EAN-13 exactly 13) rather than the check digit itself. Confirm the total digit count first, then recheck the check digit against the data digits.