A SIN error with an employer is more common than people expect — transposed digits, a number recalled from memory, a temporary SIN used before a permanent one arrived, or a newcomer using the wrong document number. The fix is usually simple if caught early. Here is exactly what to do.
Why fixing this promptly matters
Your SIN is the key the CRA uses to link your T4 to your tax account. When your employer files your T4 under an incorrect SIN:
- The income does not automatically appear in your CRA My Account or when you use Auto-fill my return
- Your CPP contributions from that employer may not credit your CPP account (affecting your eventual benefit)
- Your EI insurable hours may not accrue correctly
- If the wrong SIN belongs to a real person, their account receives an unexpected T4
The longer this goes unfixed, the more complicated the correction becomes — especially if you file your return before the T4 is amended.
Step 1: Contact your employer immediately
Reach out to your employer’s payroll or HR department and:
- Provide your correct SIN in writing (email is fine — it creates a record)
- Ask them to issue a corrected T4 with the right SIN (called an amended T4 or T4 amendment)
- Ask them to file the amended T4 with the CRA as well — the employer must correct it at the source, not just hand you a new slip
If the employer’s year-end T4 filing has already been submitted to the CRA, they need to file a T4 amendment through their payroll software or the CRA’s web-based filing system. This is a standard process for payroll departments.
Step 2: Contact the CRA
Even after the employer files the amendment, call the CRA directly to flag the issue on your account:
CRA Individual inquiries: 1-800-959-8281
Explain that a T4 was filed under an incorrect SIN and a corrected T4 is being issued. The CRA can note the correction on your file and ensure the income is linked to your correct account once the amended T4 arrives.
You can also check CRA My Account → Tax Information Slips after a few weeks to confirm the corrected T4 has appeared under your SIN. See how to use CRA My Account if you have not set it up.
Step 3: File your taxes — but handle the T4 carefully
Scenario A — Corrected T4 arrives before you file: File normally using the corrected T4. No amendment needed.
Scenario B — You need to file before the corrected T4 is ready: File on time using the income figures from the original T4 (even if it shows the wrong SIN). The employment income amounts are correct — it is only the SIN that is wrong. Once the corrected T4 is issued, file a T1 Adjustment if any figures changed.
Filing late when you owe tax triggers a 5% penalty plus 1% per month — do not delay your return just because the T4 correction is pending.
What types of SIN errors happen most often
| Error type | What to do |
|---|---|
| Transposed digits (e.g., 123 entered as 132) | Simplest fix — employer reissues T4 with correct number |
| Memorized wrong SIN | Same as above; provide a copy of your SIN card or confirmation letter |
| Used previous SIN (e.g., temporary 900-series SIN now replaced) | Contact Service Canada to confirm your current SIN; notify employer and CRA |
| Newcomer used Study/Work Permit number instead of SIN | Get your SIN from Service Canada first, then notify employer immediately |
| Someone else’s SIN entered in error | Contact employer and CRA right away — income may appear on another person’s account |
Does this affect your CPP and EI?
Yes, potentially:
- CPP contributions reported under the wrong SIN do not accumulate toward your CPP benefit. Since CPP is a lifelong entitlement based on contributions made, errors in earlier years can reduce your eventual monthly payment. The CRA and Service Canada can investigate and reallocate contributions — but this is easier to resolve promptly.
- EI insurable hours similarly track under your SIN. If you ever need to apply for EI, incomplete records can create eligibility disputes.
For more on how CPP contributions are tracked, see CPP contribution rates.
Protecting your SIN going forward
Your SIN is sensitive personal information — treat it like a password:
- Only provide it to employers, banks, and government agencies when legally required
- Do not write it on job applications before you are hired
- Shred documents containing your SIN before discarding them
- If you believe your SIN has been compromised or used fraudulently, report it to Service Canada (1-800-206-7218) and the Canadian Anti-Fraud Centre
To understand what information appears on your T4 once it is corrected, see the T4 slip explained. For the broader process of amending a filed return, see I made a mistake on my tax return.