Validate an existing barcode or calculate the missing check digit for any UPC-A, EAN-13, or GTIN-14 barcode — instantly, no signup required.
Setting up products for retail? Craftybase helps makers track what they make, what it costs, and what’s left in stock — without the spreadsheet juggling.
A check digit is the final digit of a barcode number, calculated from the preceding digits using a GS1 Mod-10 algorithm. For a UPC-A barcode like 012345678905, the 5 at the end is the check digit. It lets scanners detect typos and damaged barcodes instantly — without looking up the product.
A check digit is a single verification digit appended to the end of a barcode number. It's calculated from all the preceding digits using a mathematical formula, so if anyone makes a typo — or a scanner misreads a damaged barcode — the error shows up immediately.
Without it, a scanner would have no way to know whether 012345678905 and 012345679805 are two different products or a transcription error. With the check digit, one of those numbers is mathematically valid and the other isn't. The scanner rejects the bad one before it can cause a stock error.
How Is the Check Digit Calculated?
All GS1 barcodes (UPC-A, EAN-13, GTIN-14) use the same Mod-10 algorithm. Here's how it works, using the UPC-A barcode 01234567890? as an example:
Take all digits except the last — the 11 payload digits: 01234567890
Starting from the rightmost digit, alternate multiplying by 3 and 1 going right to left:
0 × 3 = 0
9 × 1 = 9
8 × 3 = 24
7 × 1 = 7
6 × 3 = 18
5 × 1 = 5
4 × 3 = 12
3 × 1 = 3
2 × 3 = 6
1 × 1 = 1
0 × 3 = 0
Sum the products: 0+9+24+7+18+5+12+3+6+1+0 = 85
Check digit = (10 − (85 mod 10)) mod 10 = (10 − 5) mod 10 = 5
So the complete barcode is 012345678905. The same algorithm works for EAN-13 and GTIN-14 — only the number of payload digits changes.
What Barcode Formats Use Check Digits?
Three formats are supported by this calculator, and all three use the same GS1 Mod-10 algorithm:
UPC-A (12 digits) — the standard barcode on retail products in the US and Canada. The first digit is a number system character, the next 5 identify the company, the next 5 identify the product, and the final digit is the check digit.
EAN-13 (13 digits) — the international equivalent of UPC-A, used worldwide. Adds a two-digit country prefix to the front of the UPC structure. All UPC-A barcodes are valid EAN-13 barcodes when prepended with a leading zero.
GTIN-14 (14 digits) — used for trade units (cases, pallets) and in supply chain contexts. Often printed as an ITF-14 barcode on shipping cartons. The first digit is a packaging indicator, and the rest follows the EAN-13 structure.
If a scanner won't read your barcode, the check digit is the first thing to check. Common causes:
Typo when entering digits — a single transposed digit invalidates the check. Paste your full barcode into the validator above to confirm.
Manually created barcodes — if you generated a barcode yourself without calculating the check digit, or if you appended a random final digit, the check will fail.
OCR or copy-paste errors — some digits look similar (0/O, 1/I, 6/b). The validator will tell you the expected check digit so you can compare.
Wrong format — some retailers require GTIN-14 for case-level shipments, not UPC-A. The calculator detects format from length, so you can confirm you're using the right one.
When You Outgrow This Calculator
Manually checking barcodes works for a handful of products. Once you’re managing a real range — multiple SKUs, materials, and batches — you need more than a check digit tool.
Craftybase is inventory and manufacturing software built for small-batch makers. Track your products, materials, and recipes in one place, with automatic COGS calculation on every sale. If you’re setting up barcodes to sell through retail or wholesale, it pairs well with keeping your costs and stock levels accurate on the back end.
Product makers getting into retail — if you're setting up barcodes for the first time to supply a retailer or sell on Amazon, this tool verifies your numbers before you print labels.
Makers troubleshooting scanner rejections — paste the barcode in, and you'll know within seconds if the check digit is the problem.
Wholesale and trade suppliers — GTIN-14 check digit generation for case-level and pallet barcodes used in B2B shipping.
Small-batch manufacturers — anyone creating product barcodes internally who wants to verify accuracy before committing to a print run.
E-commerce sellers — cross-checking barcodes sourced from suppliers or GS1 before entering them into Shopify, Amazon, or Etsy listings.
Frequently Asked Questions
A UPC check digit is the final digit of a Universal Product Code, calculated from the first 11 digits using the GS1 Mod-10 algorithm. Its purpose is error detection: if any digit in the barcode is misread or mistyped, the check digit calculation will produce a different result, and the scanner rejects the barcode. This prevents the wrong product from being rung up or the wrong stock level from being updated. Every GS1 barcode standard — UPC-A, EAN-13, and GTIN-14 — uses the same check digit formula.
Take the first 11 digits of your UPC-A barcode. Starting from the rightmost digit, multiply alternating digits by 3 and 1 (rightmost × 3, next × 1, and so on). Sum all the products. The check digit is (10 − (sum mod 10)) mod 10. For example, the payload 01234567890 produces a sum of 85, so the check digit is (10−5)%10 = 5, giving the complete barcode 012345678905. The calculator above does this in one step — enter your 11 digits in Generate mode and it shows the answer immediately.
UPC-A is a 12-digit barcode used on retail products in the US and Canada. EAN-13 is a 13-digit international barcode; a UPC-A is technically an EAN-13 with a leading zero. GTIN-14 is a 14-digit code used for case and pallet tracking in supply chains — the first digit is a packaging indicator. All three use the same Mod-10 check digit algorithm. The main practical difference is where they're used: UPC-A for consumer retail in North America, EAN-13 for international retail, and GTIN-14 for B2B and logistics contexts.
The most common reasons a barcode scanner rejects a barcode are: an incorrect check digit (paste the full number into the Validate mode above to confirm), a typo or transposed digits in the barcode number, OCR misreads on the printed label (especially 0/O and 1/I confusion), or using the wrong barcode format for the context (for example, a retailer expecting GTIN-14 receiving UPC-A). If the validator shows the check digit is correct, the problem is likely print quality, label damage, or a scanner configuration issue rather than the number itself.
ISBN-10 (10-digit book identifiers) uses a different algorithm — a weighted sum with modulo 11, not modulo 10 — so this calculator will not give correct results for ISBN-10. ISBN-13, however, is simply a GS1 EAN-13 barcode with the 978 or 979 prefix, and does use the same Mod-10 check digit algorithm. This calculator handles ISBN-13 correctly: enter all 13 digits in Validate mode, or the first 12 in Generate mode.
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