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Access Excel Function HKID Check Digit (last digit)

This page explains the algorithm of HKID Check Digit (last digit) and provide a custom Access Excel VBA Function to verify the Check Digit. (香港身份証最後號碼)

HKID Check Digit

Hong Kong ID card number has a last digit with bracket called “Check Digit“. Check Digit is a number to verify if the previous number and alphabet are correct. By understanding the algorithm of calculating Check Digit, you can generate a random HKID.

There are two main purposes for understand HKID Check Digit.

First, some online services only offer to local residents, they do not want overseas residents to register their service, therefore in the membership registration page, they ask you to enter a valid HKID number. The verification system cannot check whether the HKID is real, they only check if your Check Digit is valid.

Second, to check whether employee records in the database are correct, if database management system does not have this function.

Algorithm of HKID Check Digit

There are two types of HKID number:

1) Prefix with one alphabet, such as  A123456(7)

2) Prefix with two alphabets, such as AB123456(7)

I will demonstrate the algorithm below using HKID A123456(x)

Step 1

Convert the prefix alphabet to a numeric value. If Prefix contains two alphabets, add 8 to the original converted value of single alphabet, regardless of the first alphabet.

For example, A should convert to 8, then AA (or BA,CA,DA, etc) should be converted to 8+8 = 16

In our example HKID A123456(x), the result is 8

Prefix Alphabet Converted value A 8 B 16 C 24 D 32 E 40 F 48 G 56 H 64 I 72 J 80 K 88 L 96 M 104 N 112 O 120 P 128 Q 136 R 144 S 152 T 160 U 168 V 176 W 184 X 192 Y 200 Z 208 xA 16 xB 24 xC 32 xD 40 xE 48 xF 56 xG 64 xH 72 xI 80 xJ 88 xK 96 xL 104 xM 112 xN 120 xO 128 xP 136 xQ 144 xR 152 xS 160 xT 168 xU 176 xV 184 xW 192 xX 200 xY 208 xZ 216

Step 2

Convert each HKID digit to a number.

Nth HKID digit multiplier 1st 7 2nd 6 3rd 5 4th 4 5th 3 6th 2

In our example HKID A123456(x)

1 is the 1st digit, multiply 1 by 7 = 7

2 is the 2nd digit, multiply 2 by 6 = 12

3 x 5 = 15

4 x 4 = 16

5 x 3 = 15

6 x 2 = 12Total =  77

Step 3

Calculate remainder of (Result 1 + Result 2)/11

= (8+77)/11

= 8

Step 4

Check Digit = Deduct 11 by result of Step 3

= 11 – 8

= 3

Now we know HKID A123456 should have 3 in the bracket, that is A123456(3)

If Check Digit = 10, convert to A

If Check Digit = 11, convert to 0

VBA Code of custom Access Excel Function – HKID Check Digit

Public Function wCheckHKID(ID As String) As String     Dim newIDArr() As Variant     newID = UCase(Replace(Replace(ID, "(", ""), ")", ""))     lenNewID = Len(newID)     IDnoDigit = Left(newID, lenNewID - 1)     lenIDnoDigit = Len(IDnoDigit)     For i = 1 To lenIDnoDigit         ReDim Preserve newIDArr(i)         newIDArr(i) = Mid(IDnoDigit, i, 1)     Next i     If lenIDnoDigit = 7 Then         checkSum = (Asc(newIDArr(1)) - 64) * 8 + newIDArr(2) * 7 + newIDArr(3) * 6 + newIDArr(4) * 5 + newIDArr(5) * 4 + newIDArr(6) * 3 + newIDArr(7) * 2         checkDigit = 11 - checkSum Mod 11     ElseIf lenIDnoDigit = 8 Then         checkSum = 6 + (Asc(newIDArr(2)) - 64) * 8 + newIDArr(3) * 7 + newIDArr(4) * 6 + newIDArr(5) * 5 + newIDArr(6) * 4 + newIDArr(7) * 3 + newIDArr(8) * 2         checkDigit = 11 - checkSum Mod 11     End If     If checkDigit = 10 Then         newCheckdigit = "A"     ElseIf checkDigit = 11 Then         newCheckdigit = "0"     Else: newCheckdigit = checkDigit     End If     If Asc(newCheckdigit) = Asc(Right(newID, 1)) Then         wCheckHKID = True     Else         wCheckHKID = False     End If End Function

Syntax of custom Access Excel Function – HKID Check Digit

wCheckHKID (ID)

ID Full HKID such as Z123456(2), accept values with or without brackets, lower case or upper case

K.Will - Last Digit

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