UPC Barcode Check Digits

UPC barcodes include a check digit. The UPC check digit is the 12th digit in the lower-right corner of the barcode. Here's how to calculate a UPC barcode check digit

The last digit in a UPC barcode is a check digit based on the previous 11 numbers. Our example barcode data is "41234554321"

Add up the numbers in the odd positions left to right. Multiple the result by 3. Add up the numbers in the even positions. Now add the first subtotal to the second. The UPC barcode check digit is the single digit number makes the total a multiple of 10.

4+2+4+5+3+1=19 19x3=57 1+3+5+4+2=15 57+15=72 and 8 makes 80

In VBA/Visual Basic it looks something like this:

Option Explicit

Function Azalea_UPC_A_checkDigit(ByVal UPCnumber As String) As String
' 18dec08 Jerry Whiting
' Copyright 2008 Azalea Software, Inc. All rights reserved. www.azalea.com
' Your input, UPCnumber, is an 11 character string for a UPC version A barcode.
' This function calculates the check digit value for your 11-digit input.

Dim checkDigitSubtotal As Integer ' check digit throwaway

' Valid input is 11-digits (no check digit), 12-digits (with check digit), or 14-digits (GTIN).
Select Case Len(UPCnumber)
Case 11
' do check digit calculation
Case 12
' lets ignore your check digit & use ours
UPCnumber = Left(UPCnumber, 11)
Case 14
' GTIN input, strip leading 2 characters & last one too;
UPCnumber = Mid(UPCnumber, 3, 11)
Case Else
' error handling goes here
End Select

' do the check digit
checkDigitSubtotal = (Val(Left(UPCnumber, 1))) + (Val(Mid(UPCnumber, 3, 1))) + (Val(Mid(UPCnumber, 5, 1))) + (Val(Mid(UPCnumber, 7, 1))) + (Val(Mid(UPCnumber, 9, 1))) + (Val(Right(UPCnumber, 1)))
checkDigitSubtotal = (3 * checkDigitSubtotal) + (Val(Mid(UPCnumber, 2, 1))) + (Val(Mid(UPCnumber, 4, 1))) + (Val(Mid(UPCnumber, 6, 1))) + (Val(Mid(UPCnumber, 8, 1))) + (Val(Mid(UPCnumber, 10, 1)))

Azalea_UPC_A_checkDigit = Right(Str(300 - checkDigitSubtotal), 1)

End Function

The wizard utility bundled with UPCTools calculates the UPC version A check digit. All of the free sample code for UPCTools does too.