# Luhn check-digit calculator, IMEI, credit cards, ...

## Verify a number that ends in a Luhn check-digit

Enter the number including its right most check-digit:
 number: is valid:

## Calculate a Luhn check digit

Enter the number without the right most check-digit:

number -- checkdigit: --

## Calculate number length

Remove non number characters (dots, dashes, space..) and calculate the length:

number: => len:

## Luhn check digits in credit-card numbers

The Luhn algorithm is not used to protect against fake card numbers. The last digit on your credit card number is just there to be able to quickly identify an accidental typo.
• Most credit card numbers are 16 digits long but they may be up to 19 digits long.
• A variable length of digits on the left identify the issuer such as Visa or Mastercard. This field is 1 to 6 digits long.
• The right most digit is a Luhn check digit

## Luhn check digits in IMEI numbers

An IMEI (International Mobile Equipment Identity) is a hardware identifier for a mobile phone. They are like serial numbers but the left most digits contain information about the type of mobile phone. You can get the IMEI of your phone by typing *#06# "call" on your mobile phone. This will display the full 15 digit IMEI which includes a check digit in the right most position. Within the network the IMEI may be transmitted as IMEI, or IMEI with the check digit set to zero or as IMEISV.
• IMEI = TTTTTTTT-NNNNNN-D , 15 digits long =14 digits + check digit
• IMEI with check digit set to zero = TTTTTTTT-NNNNNN-0 , 14 digits + 0
• IMEISV without check digit and a software version number = TTTTTTTT-NNNNNN-SS , 14 digits + two digits for version = 16 digits in total

T=Type Allocation Code = phone model and manufacturer identifier, first 8 digits of the IMEI
N=serial number
D=check digit
S=mobile phone software version number

To calculate a valid IMEI with check digit from either a IMEI or a IMEISV one would use the first 14 digits and enter it in the above "Calculate a Luhn check digit" form.