Home›Glossary›SIN

SIN

General

Canada Social Insurance Number

A unique 9-digit number issued by Service Canada, required for employment, tax filing, and government benefits in Canada. Validated using the Luhn checksum algorithm.

Definition

A Social Insurance Number (SIN) is a unique 9-digit identifier issued by Service Canada to individuals working or receiving government benefits in Canada. It plays a role similar to a Social Security Number in the United States, required for employment, tax filing, and accessing programs like Employment Insurance and the Canada Pension Plan.

Like several other national identifiers, the SIN includes a built-in checksum, which lets systems catch many transcription errors, a transposed digit or single typo, before the number is ever submitted to Service Canada. The Canada SIN Validator checks this automatically.

Formula

A SIN is validated using the Luhn algorithm:

  1. Starting from the rightmost digit, double every second digit.
  2. If doubling produces a number greater than 9, subtract 9 from it.
  3. Sum all 9 digits.
  4. The SIN is valid if the sum is evenly divisible by 10.

Worked Example

For the SIN 046 454 286 (046454286), applying the Luhn algorithm, doubling every second digit from the right and adjusting any result over 9, produces a total sum of 50.

Since 50 ÷ 10 = 5 with no remainder, the checksum passes, confirming the number is structurally valid.

Key Things to Know

  • First digit is never 0: SINs starting with 0 are never assigned and always fail validation.
  • First digit 9 means temporary resident: these SINs are issued to work or study permit holders and have an expiry date.
  • Same algorithm as credit cards: the Luhn checksum used for SIN validation is identical to the one used for card numbers.
  • A passing checksum isn't proof of registration: it only confirms the number is correctly formed, not that it's been issued to a real person, only Service Canada can confirm that.

Related Terms

NINUK National Insurance NumberPANPermanent Account Number

Frequently Asked Questions

What is a Social Insurance Number used for?
A SIN is required to work in Canada, file taxes, and access government benefits and programs such as Employment Insurance and the Canada Pension Plan. Employers and financial institutions request it for tax reporting purposes.
What does it mean if a SIN starts with 9?
SINs beginning with 9 are issued to temporary residents, such as work or study permit holders, rather than citizens or permanent residents. These SINs carry an expiry date tied to the holder's immigration document.
How is a SIN validated?
A SIN is checked using the Luhn algorithm, the same checksum used to validate credit card numbers, which doubles every second digit from the right, adjusts for any result over 9, and confirms the total sum is divisible by 10.
Can a SIN start with 0?
No, the first digit of a SIN is never 0, since that value is not assigned under Service Canada's numbering scheme. A SIN starting with 0 always fails validation.
Where can I find my SIN if I've lost it?
Your SIN appears on your SIN confirmation letter from Service Canada and on tax documents such as your T4 slip. If you can't locate it, you can request confirmation directly through Service Canada.