From the AEGIS e-Journal, Volume 2 Number 3, March 1999
The Canadian SIN is similar to a SSN in that the number is issued to all Canadian citizens and, just like the SSN, it was never intended to be an identifier - but it is. And, just like the American SSN, the Canadian SIN has nine digits. The similarity in how to determine a "real" one from a "randomly printed" one ends there. There is a formula that can be applied to the SIN that will weed out some of the fake ones. Here goes: 1. Write down the first eight digits (of the nine digit number). 2. Double every second digit. If the number doubled equals more than 10, subtract 9. 3. Add all the odd digits, plus the answers from the doubling exercise above. 4. The ninth digit of the SIN will be the amount needed to make the total from #3 divisible by 10. This is somewhat confusing, so let's do an example right here. 1. Write first 8 digits of the SIN: 1-2-3-4-5-6-7-8-? 2. Double every second digit: 2 doubled is 4 4 doubled is 8 6 doubled is 12, so subtract 9 = 3 8 doubled is 16, so subtract 9 = 7 This total is now 22. 3. Add all the odd digits. 1+3+5+7+22 (the answer to the doubling above) - which totals 38. 4. 38 + ? is divisible by 10. Therefore, the "?" is 2. This means that SIN 12345678 - 2 - is the only valid SIN starting with 12345678.