🔢 Check Digit Calculator
Calculate check digit for numbers
Enter the number without the check digit
How to Use This Calculator
Enter Number
Input the number without the check digit. The calculator will calculate the check digit for you.
Select Method
Choose the check digit calculation method: Luhn Algorithm (used for credit cards, IMEI numbers) or Mod 10.
Review Check Digit
See the calculated check digit and the complete number with the check digit appended.
Formula
Luhn Algorithm: Sum digits (double every other digit, subtract 9 if > 9), then (10 - (sum % 10)) % 10
Mod 10: Multiply digits by 2 or 1 alternately, sum, then (10 - (sum % 10)) % 10
Luhn Algorithm Example:
For number "123456789":
• Process digits from right to left, doubling every other digit
• Sum all digits
• Check digit = (10 - (sum % 10)) % 10
• Check digit = 7 (full number: 1234567897)
About Check Digit Calculator
A check digit calculator helps you calculate check digits for numbers using various algorithms like the Luhn algorithm or Mod 10 method. Check digits are used to verify the validity of numbers and detect errors in data entry or transmission. The Luhn algorithm is commonly used for credit card numbers, IMEI numbers, and other identification numbers. This calculator helps you generate check digits for numbers, which is useful for validation, error detection, and data integrity.
When to Use This Calculator
- Number Validation: Calculate check digits for number validation
- Error Detection: Generate check digits to detect data entry errors
- Credit Cards: Calculate check digits for credit card numbers (Luhn)
- IMEI Numbers: Calculate check digits for IMEI numbers (Luhn)
Understanding Check Digits
- Luhn Algorithm: Most common algorithm for credit cards and IMEI numbers
- Mod 10: Alternative method for check digit calculation
- Error Detection: Check digits help detect single-digit errors and some transposition errors
- Validation: Used to validate number integrity
Why Use Our Calculator?
- ✅ Check Digit Generation: Calculate check digits for numbers
- ✅ Multiple Methods: Support for Luhn and Mod 10 algorithms
- ✅ Validation: Verify number integrity
- ✅ Error Detection: Detect data entry errors
- ✅ 100% Free: No registration or payment required
Frequently Asked Questions
What is a check digit?
A check digit is a digit added to a number to verify its validity and detect errors. Check digits are calculated using algorithms like the Luhn algorithm or Mod 10 method. They help detect single-digit errors and some transposition errors in number entry. Check digits are commonly used in credit card numbers, IMEI numbers, barcode numbers, and other identification numbers.
How does the Luhn algorithm work?
The Luhn algorithm (also known as the "modulus 10" algorithm) works by: (1) Starting from the rightmost digit, double every other digit (2nd from right, 4th from right, etc.), (2) If doubling results in a two-digit number, subtract 9, (3) Sum all digits, (4) The check digit is (10 - (sum % 10)) % 10. This algorithm is used by most credit cards and IMEI numbers.
What's the difference between Luhn and Mod 10?
The Luhn algorithm is a specific implementation of a Mod 10 check digit algorithm. While both are Mod 10 algorithms (both use modulo 10 arithmetic), the Luhn algorithm has specific rules for doubling digits and handling two-digit results. Other Mod 10 implementations may use different multiplication patterns or weighting schemes. The Luhn algorithm is the most common and is used by credit cards and IMEI numbers.
Can I use this to validate credit card numbers?
Yes, you can use this calculator to calculate the check digit for credit card numbers using the Luhn algorithm. However, this calculator only calculates the check digit - it doesn't validate the entire credit card number or check if it's a valid, active card. For full credit card validation, you'd need additional checks like card number length, issuer identification, and account validation through the card network.