IMEI (International Mobile Equipment Identity) number is a unique number associated with every mobile phone as its identity. There is an interesting maths theory behind each IMEI number. Its last digit is computed according to Luhn Algorithm. Before 2003 this check digit was always set to 0. After revision of GSMA guidelines it has changed.

Here I am describing how the last digit of any IMEI number is calculated. The last number is also called a check digit and can be calculated using the Luhn algorithm.

Note down your first 14 digits of IMEI number from left side. You can get this displayed on the screen of the phone by typing *#06#

Let your IMEI number is 351868011872996. We will find its last (15th) digit by calculation using first 14 digits.

Step 1: Note down first 14 digits of IMEI number.
Step 2: Multiply alternate digits by 2 starting from right hand side.
Step 3: Add digits of each cell.
Step 4: Added result.
Step 5: Add digits of all cells.

Step 135186801187299
Step 23101166160211674918
Step 331+011+661+60211+67491+8
Step 431176702177499
Step 53 + 1 + 1 + 7 + 6 + 7 + 0 + 2 + 1 + 7 + 7 + 4 + 9 + 9 = 64

Total Sum = 64
Next higher value of 64 in multiple of 10 is 70.
So our desired last digit = 70-64 = 6.
It matches with our original IMEI number.

Try yourself with another IMEI. Check if it comes true?

Hints for finding IMEI number

•   Generally the IMEI number can be retrieved by entering *#06#
•   In some older Sony Ericsson handsets, it can be seen by pressing these keys: * Right * Left Left * Left *
•   On BlackBerry and on new Sony Ericsson devices can also be found by going to options=>status.
•   On Android the IMEI information can be found under the "About Phone" menu option in the settings menu.