Free UPC & GTIN Check Digit Calculator

What Is a Check Digit?

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:

1. Take all digits except the last — the 11 payload digits: 01234567890
2. 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
3. Sum the products: 0+9+24+7+18+5+12+3+6+1+0 = 85
4. 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.

For a deeper look at setting up barcodes for your products, see our guide to generating UPC barcodes.

Why Is My Barcode Scanner Rejecting My Barcode?

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 growing range, it's worth having your inventory software do the checking automatically.

Craftybase stores barcodes for each of your products and materials, and can scan them in when you receive stock or record a sale. There's no manual digit verification — the system validates automatically and updates your inventory in real time.