Free Check Digit Calculator

Worked example: EAN-13

Start with the twelve data digits 590123412345. Counting from the rightmost data digit, multiply alternate digits by 3 and 1. The weighted sum is 83. The next multiple of ten is 90, so the check digit is 7 and the complete number is 5901234123457. This is example data, not a retail number assigned to your product.

To repeat the calculation here, choose GTIN-13 and paste the twelve data digits. To verify an existing number, paste all thirteen digits instead. A valid result confirms the arithmetic only: it does not confirm the product name, ownership of the identifier, registration with GS1 or the quality of a printed barcode.

Avoid common input mistakes

Keep leading zeroes when copying from a spreadsheet. Format the identifier column as text before importing or entering numbers, because a spreadsheet may remove a leading zero or display a long number in scientific notation. Check that you selected the format matching the full identifier, including its final check digit.

If a supplied number fails, compare it against the original label or supplier record. Do not replace a digit just to make the calculator show a valid result: that could create a different identifier. Code 128 and Code 39 use different rules and are not verified by this GTIN modulo-10 calculator.

How the modulo-10 check digit works

Reading the number from the right, each digit is multiplied alternately by 3 and 1. The products are added together, and the check digit is whatever takes that sum up to the next multiple of ten. A valid check digit catches most single-digit typing mistakes and many transpositions, which is why scanners reject numbers that fail it.

Getting a valid check digit does not make a number yours. Retail identifiers are licensed by GS1 and ISBNs by your national agency.