Check Digit

Definition of Check Digit

A check digit is a numerical or alphanumeric character added to a string of numbers, such as a product’s serial number or a credit card number, for the purpose of error detection. It is calculated using a specific algorithm based on the other digits in the sequence. By verifying the check digit, systems can quickly determine if the data has been entered accurately and catch potential errors before processing.


The phonetics of the keyword “Check Digit” using the International Phonetic Alphabet (IPA) is: /ʧɛk ˈdɪʤɪt/

Key Takeaways

  1. A Check Digit is a form of redundancy used in error detection algorithms, designed to catch common data entry errors by verifying the integrity of input data.
  2. Check Digits are widely used in scenarios such as ISBN numbering for books, International Mobile Equipment Identity (IMEI) numbers for smartphones, and bank account numbers.
  3. There are several methods of calculating Check Digits, such as the Modulus 10 (Luhn) algorithm, the Modulus 11 algorithm, and the Verhoeff algorithm, each serving specific purposes and providing different levels of error detection.

Importance of Check Digit

The term “Check Digit” is important in the world of technology because it plays a crucial role in ensuring data integrity and preventing errors in various identification systems.

A check digit is an additional digit appended to a numerical identifier, such as a credit card number, barcodes, or International Standard Book Numbers (ISBNs), which helps to verify whether the identifier has been inputted or transmitted correctly.

By employing self-checking algorithms, check digits can detect common issues like single-digit errors or transposition errors, reducing the chances of errors and unintended consequences.

As a result, check digits greatly enhance the reliability and efficiency of data processing in an increasingly digitized world where accurate information is key.


The primary purpose of a check digit is to ensure the accuracy and validity of data, particularly in identification codes, account numbers, or any string of digits that need to be regularly input into various systems. Check digits are designed to detect and prevent errors that can occur during data entry or processing operations by serving as a built-in tool for error detection.

By integrating a check digit within a sequence of numbers, systems can self-perform validations to minimize the chances of entering incorrect or invalid information. This increases the reliability and integrity of the data, as well as enhances the efficiency of the overall system by mitigating the need for manual verification processes.

In various industries, check digits find extensive application due to their integral role in maintaining data accuracy in their respective systems. For instance, in the realm of finance, check digits form an essential component of credit card numbers, bank account numbers, and routing numbers, ensuring the prevention of illicit transactions.

Similarly, in logistics and supply chain management, check digits are integrated into tracking numbers, barcodes, and International Standard Book Numbers (ISBNs) to validate product and shipment information. This enhanced accuracy not only improves operations across organizations but also instills confidence among users regarding the correctness of data being processed.

Examples of Check Digit

A check digit is a single numerical digit added to a larger number, which is used to verify the accuracy and authenticity of the number. It is calculated using a specific algorithm based on the other digits in the number. Here are three real-world examples of check digit technology:

International Standard Book Number (ISBN): ISBN is a unique identifier assigned to books, which consists of either 10 or 13 digits. The last digit of an ISBN is a check digit computed using a specific algorithm, which helps ensure the accuracy and validity of the number. It helps reduce errors during data entry and prevents counterfeit books from being mistaken as genuine.

Universal Product Code (UPC): UPC is a 12-digit barcode used globally for tracking products in retail stores. The last digit of a UPC is a check digit, calculated using the first 11 digits. It helps verify that the barcode has been correctly scanned or entered, reducing the likelihood of errors during inventory management and point-of-sale transactions.

International Mobile Equipment Identity (IMEI): IMEI is a unique 15-digit number assigned to each mobile device, like smartphones and tablets. The last digit of IMEI serves as a check digit computed using the Luhn algorithm. This check digit helps confirm the authenticity of the device while minimizing errors during data entry. Additionally, it allows tracing lost or stolen devices and prevents them from being registered with a different mobile network operator.

Check Digit FAQ

What is a check digit?

A check digit is a numeric or alphanumeric character used in various numbering systems to verify the accuracy and authenticity of identification numbers. It is typically calculated as a function of the rest of the sequence, helping to identify errors in data entry or transcription.

How does a check digit work?

A check digit is calculated using a specific algorithm based on the other digits in the identification number. When the number is entered or scanned, the algorithm calculates the check digit from the other digits, and if it matches the given check digit, the entry is considered valid. If not, an error is flagged.

What are some common check digit algorithms?

There are several check digit algorithms used across various industries and applications, including Luhn algorithm (used in credit card numbers), International Standard Book Number (ISBN) algorithm, Verhoeff algorithm, and Damm algorithm.

Why are check digits important?

Check digits serve as an essential part of data validation, helping ensure the integrity and accuracy of the identification numbers used in processes such as barcoding, inventory management, and e-commerce. They help prevent errors in data entry and reduce the risk of fraudulent or incorrect data being processed.

Can check digits be letters?

Yes, check digits can be alphanumeric characters, depending on the specific algorithm and numbering scheme being used. For example, the check digit for an ISBN-13 number may be a letter as well as a digit.

Related Technology Terms

  • Data Validation
  • Error Detection
  • Modulus Algorithm
  • Barcode Verification
  • International Standard Book Number (ISBN)

Sources for More Information

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