The check digit lets scanners detect most typing and scanning errors. GS1 issues company prefixes; you can’t make up valid retail barcodes, but you can verify or complete one. Everything is calculated in your browser, so nothing you type is sent to our server.
How to use the Check Digit Calculator
- Barcode digits (without the check digit)
- Leading zeros to add
Everything runs in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
Type the barcode digits without the check digit; add leading zeros to convert between formats (e.g. UPC to GTIN-14).
Tips
- Know the difference between margin (profit ÷ price) and markup (profit ÷ cost).
- Apply successive discounts one after another – they do not simply add up.
- Check whether prices already include sales tax or VAT.
- Round prices only at the very end of the calculation.
Common mistakes to avoid
- Adding discount percentages together.
- Pricing from a target margin using the markup formula.
- Forgetting payment-processing and shipping fees.
Formula
From the right (excluding the check digit), multiply digits alternately by 3 and 1Sum the productsCheck digit = (10 − sum mod 10) mod 10Worked example
Inputs — Barcode digits (without the check digit): 62910415002; Leading zeros to add: 0.
Results — Check digit = 4; Complete code = 629104150024; Code type = GTIN-12 (UPC-A).
Frequently asked questions
What is a check digit?
The last digit of a barcode, calculated from the others to catch errors.
How is a UPC check digit calculated?
Weights 3 and 1 alternate from the right; the check digit brings the sum to a multiple of 10.
Is the ISBN-13 check digit the same?
Yes – ISBN-13 uses the EAN-13 algorithm.
What formula does the Check Digit Calculator use?
From the right (excluding the check digit), multiply digits alternately by 3 and 1.