Barcode Check Digit

Automatically calculate the check digit for EAN-13, UPC, ISBN, and other barcode formats. Validate barcode integrity with this free online check digit calculator.

How to Use

  1. Select barcode type

    Choose the barcode format: EAN-13, UPC-A, ISBN, or others.

  2. Enter digits

    Input the barcode digits excluding the check digit.

  3. View results

    Click Calculate to see the check digit and the complete barcode number.

What is a check digit?

A check digit is a single verification digit added to the very end of a barcode number such as EAN-13 or UPC. Because it is calculated from the leading digits using a fixed rule, even a single mistyped or misread digit will no longer match the recalculated value, so the error is caught instantly.

Why is it needed?

Barcodes are scanned thousands of times across logistics, POS, and inventory systems, and a single wrong digit being read as a different product can cause serious confusion. The check digit is a self-checking mechanism that verifies integrity from the number alone, without any extra communication, filtering out single-digit errors and most adjacent transposition errors.

  • EAN-13: the 13th check digit is derived from the first 12 digits
  • UPC-A: the 12th check digit is derived from the first 11 digits (a subset of EAN-13)
  • GS1 SSCC, ITF-14, and others use the same Mod 10 principle

Calculation formula

The EAN-13 check digit is computed using the modulo 10 (Mod 10) method.

check digit = (10 − (weighted sum % 10)) % 10

The weighted sum is obtained by multiplying each of the first 12 digits by its positional weight and adding the results. The 1st, 3rd, 5th… positions (odd positions) are multiplied by ×1, and the 2nd, 4th, 6th… positions (even positions) by ×3.

Example (880123456789):
8×1 + 8×3 + 0×1 + 1×3 + 2×1 + 3×3 + 4×1 + 5×3 + 6×1 + 7×3 + 8×1 + 9×3 = 127
127 % 10 = 7 → 10 − 7 = 3 → complete barcode 8801234567893

If the weighted sum is a multiple of 10, then (10 − 0) % 10 = 0, so the check digit becomes 0.

Frequently Asked Questions

What is a check digit?
A check digit is the last digit of a barcode, calculated from the preceding digits to verify the accuracy of the entire number. It can instantly detect typing or scanning errors.
What algorithm calculates the check digit?
EAN/UPC barcodes use the Modulo 10 (Mod 10) algorithm. Odd positions are multiplied by ×1 and even positions by ×3 to get a weighted sum, then the check digit is (10 − weighted sum % 10) % 10.
How is an EAN-13 barcode structured?
EAN-13 consists of a 2–3 digit country (GS1) code, a manufacturer code, a product code, and a final single check digit. For example, a code starting with 880 is a product registered with GS1 Korea.
What is the difference between EAN-13 and UPC-A?
EAN-13 is the 13-digit international standard and UPC-A is the 12-digit North American standard. Adding a leading zero to a UPC-A turns it directly into an EAN-13, so the two systems are compatible under the same Mod 10 algorithm.
What is the role of the check digit?
When a scanner reads a barcode, it recalculates the check digit from the leading digits and compares it with the actual last digit. If the two differ, the read is treated as faulty and a rescan is requested, preventing the wrong product from being registered.
Why is only the even position multiplied by 3?
Alternating between 1 and 3 also catches 'transposition errors' where two adjacent digits are swapped. When two digits are swapped, the weights change so the weighted sum changes, making the check digit mismatch.
Can the check digit be 0?
Yes. If the weighted sum is an exact multiple of 10 (e.g., 120, 130), the remainder is 0, so (10 − 0) % 10 = 0, meaning the check digit is 0. Thus 0 is also a valid check digit value.
Can this calculator validate ISBN too?
The 13-digit ISBN-13 uses the same Mod 10 algorithm as EAN-13, so it is calculated directly. However, the older 10-digit ISBN-10 uses weights 1–10 and Mod 11, so its method is different.
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