APPENDIX B: NUMBER VALIDATIONS
Modulus 10 Check on Income Tax Number
This validation is performed when the Income Tax number is completed or when the PAYE reference number starts with 0, 1, 2, 3, or 9. The last character is a check digit calculated using the following algorithm:

Digit 1: Multiply by 2 and add the result to the total.
Digit 2: Add to the total.
Digit 3: Multiply by 2 and add the result to the total.
Digit 4: Add to the total.
Digit 5: Multiply by 2 and add the result to the total.
Digit 6: Add to the total.
Digit 7: Multiply by 2 and add the result to the total.
Digit 8: Add to the total.
Digit 9: Multiply by 2 and add the result to the total.
When the result of a line item calculation exceeds 9, the individual digits are added together to obtain a single-digit result (e.g., 18 = 1 + 8 = 9). The check digit (Digit 10) is determined by summing the results of each line item calculation. If the last digit of the total is greater than 0, the check digit is equal to 10 minus the last digit of the total. If the last digit of the total is 0, the check digit is zero.

Example 1:

Tax Reference Number: 0001339050
Calculations:
Digit 1: 0 x 2 = 0
Digit 2: 0
Digit 3: 0 x 2 = 0
Digit 4: 1
Digit 5: 3 x 2 = 6
Digit 6: 3
Digit 7: 9 x 2 = 18 (1 + 8 = 9)
Digit 8: 0
Digit 9: 5 x 2 = 10 (1 + 0 = 1)
Total: 20
The last digit of the total is 0, so the check digit is 0, and the number is valid.
Example 2:

Tax Reference Number: 0667056642
Calculations:
Digit 1: 0 x 2 = 0
Digit 2: 6
Digit 3: 6 x 2 = 12 (1 + 2 = 3)
Digit 4: 7
Digit 5: 0 x 2 = 0
Digit 6: 5
Digit 7: 6 x 2 = 12 (1 + 2 = 3)
Digit 8: 6
Digit 9: 4 x 2 = 8
Total: 38
The last digit of the total is 8, so the check digit is 10 – 8 = 2, and the number is valid.
Modulus 10 Check on PAYE/SDL/UIF Reference Number
For PAYE, SDL, and UIF reference numbers, the first digit must be replaced with a 4. The following algorithm is applied:

Digit 1: Replace with 4 and multiply by 2, then add the result to the total.
Digit 2: Add to the total.
Digit 3: Multiply by 2 and add the result to the total.
Digit 4: Add to the total.
Digit 5: Multiply by 2 and add the result to the total.
Digit 6: Add to the total.
Digit 7: Multiply by 2 and add the result to the total.
Digit 8: Add to the total.
Digit 9: Multiply by 2 and add the result to the total.
Example:

PAYE/SDL/UIF Reference Number: 7230767891
Calculations:
Digit 1: Replace with 4, 4 x 2 = 8
Digit 2: 2
Digit 3: 3 x 2 = 6
Digit 4: 0
Digit 5: 7 x 2 = 14 (1 + 4 = 5)
Digit 6: 6
Digit 7: 7 x 2 = 14 (1 + 4 = 5)
Digit 8: 8
Digit 9: 9 x 2 = 18 (1 + 8 = 9)
Total: 49
The last digit of the total is 9, so the check digit is 10 – 9 = 1, and the number is valid.
Modulus 13 Check on ID Number
Only valid ID numbers are allowed, and a modulus 13 check must be performed on all ID numbers. The control figure, which is the 13th digit of the identity number, is calculated using the following formula:

Add all the digits in the odd positions, excluding the last digit.
Example: ID Number 8001015009087: 8 + 0 + 0 + 5 + 0 + 0 = 13
Move the even positions into a field and multiply the number by 2.
Example: 011098 x 2 = 22196
Add the digits of the result from step 2.
Example: 2 + 2 + 1 + 9 + 6 = 20
Add the result from step 3 to the result from step 1.
Example: 13 + 20 = 33
Subtract the second digit of the result (i.e., 3) from 10.
If the result is a two-digit number, use the last digit to compare against the last number in the ID Number. If the result differs, the ID number is invalid.