How to validate a SIN number: the Luhn check, worked out.

How to validate a SIN number by hand

1. Check the shape. Remove spaces and hyphens. You need exactly nine digits.
2. Double every second digit. Positions 2, 4, 6 and 8 counting from the left.
3. Collapse results above 9. Add the two digits (or subtract 9): 16 becomes 1 + 6 = 7.
4. Add all nine values. The untouched digits at positions 1, 3, 5, 7 and 9 plus the adjusted ones.
5. Test the total. A multiple of 10 passes.

Worked example

Take the public example 046 454 286. Digits: 0, 4, 6, 4, 5, 4, 2, 8, 6. Doubling positions 2, 4, 6 and 8 gives 8, 8, 8 and 16 (counted as 7). The nine values are 0, 8, 6, 8, 5, 8, 2, 7, 6, which add up to 50. Fifty is a multiple of 10, so it passes. Change the last digit to 7 and the total becomes 51, so it fails.

Why this works: the check digit

The ninth digit is chosen so the total comes out as a multiple of 10. Because doubling a digit and collapsing it gives a different result for each of 0 to 9, changing any one digit always changes the total, so every single-digit typo is caught. Swapping neighbours is caught except for a few cases; the pair 0 and 9 is the known blind spot (09 and 90 give the same contribution). The tool above computes this for your own number instead of asking you to take it on trust.

Where the SIN checksum comes from

The Luhn scheme is the mod-10 check digit method in ISO/IEC 7812-1 (Luhn check digit), also used on payment cards. Service Canada does not publish the SIN check-digit rule on the pages we reviewed, so treat this as the standard, widely implemented method rather than an official statement, and as a typo detector only.

What validation cannot do

A passing SIN may never have been issued, and a failing one is almost always a typo. Service Canada says your SIN is private and it is illegal for anyone else to use it, and we know of no public lookup; employers who need to confirm a SIN are directed to Service Canada. Use the SIN validator for a quick yes or no, the test number generator for fixtures, and the format guide for the written layout.

Frequently asked questions

How do you validate a SIN number?

Confirm nine digits, double the 2nd, 4th, 6th and 8th digits (collapsing any result above 9), add all nine values, and check the total is a multiple of 10.

What is the SIN check digit?

The ninth digit. It is chosen so the Luhn total is a multiple of 10, which lets software catch typing errors.

Does a valid SIN mean it belongs to someone?

No. The check only tests internal consistency. Only Service Canada can confirm a SIN was issued.

Does the Luhn check catch every typo?

It catches every single wrong digit and nearly every swap of neighbouring digits, but not swapping a 0 and 9 that sit next to each other.

Does the SIN use the same check as a credit card?

The arithmetic is the same Luhn mod-10 scheme, but a card number has a different length and rules, so a number valid for one is not valid for the other.

Sources (retrieved October 2026): Service Canada: Social Insurance Number; ISO/IEC 7812-1 (Luhn check digit). TNAADO is not affiliated with the Government of Canada; this page is general information, not legal or immigration advice.