Check Digit Calculator
Calculate and validate check digits for various numbering systems.
Table of Contents
How to Use
- Select the algorithm (Luhn, Modulo 10/11, EAN-13, or ISBN-10).
- Enter the number without the check digit.
- Click Calculate to generate the check digit.
- View the calculated check digit and full number with validation status.
What Is a Check Digit?
A check digit is a form of redundancy check used for error detection in identification numbers. It's calculated from the other digits in the number and helps verify that the number was correctly entered or transmitted.
Check digits are widely used in credit card numbers, barcodes (UPC, EAN), ISBNs, and many other identification systems to catch transcription errors.
Common Check Digit Algorithms
- Luhn Algorithm: Used for credit card numbers, detects single-digit errors and most transpositions
- Modulo 10: Simple sum-based algorithm, adds all digits and uses remainder
- Modulo 11: Weighted sum with modulo 11, used in ISBN-10 and some national IDs
- EAN-13: Used for retail product barcodes worldwide
- ISBN-10: Specific algorithm for 10-digit International Standard Book Numbers
Frequently Asked Questions
- What is the Luhn algorithm used for?
- The Luhn algorithm is primarily used to validate credit card numbers, IMEI numbers, and other identification numbers. It can detect single-digit errors and most adjacent digit transpositions.
- Can I validate an existing number with check digit?
- Yes! Enter the complete number including the check digit. The calculator will verify if the check digit is correct by recalculating it and comparing.
- What does 'X' mean in ISBN-10 check digits?
- In ISBN-10, if the check digit calculation results in 10, it's represented as 'X' since check digits must be a single character.