# The secret Barcode Check Digit - how it's calculated

# The secret Barcode Check Digit – how it’s calculated

Most people know that the last digit of a barcode is a “check digit” used by the scanner to check whether it read the barcode correctly. It does this by adding up and multiplying the numbers it gets from the bars. The secret formula for the last digit is:

1. Add together the value of all of the digits in odd positions

(digits 1, 3, 5, 7, and 9).

2. Multiply that number by 3.

4. Add together the value of all of the digits in even positions

(digits 2, 4, 6, 8 and 10).

4. Add this sum to the value in step 2.

5. Take the number in Step 4 and add just enough to equal a multiple of 10. That number is the check digit.

7+9+8+0+5+2 =31 x 3 = 93

0+5+7+7+0=19 + 93 = 112 + 8 = 120