Nobody files a perfect tax return every year. Whether you forgot to claim a deduction, made a math error, received an amended T4 slip, or simply learned about a credit you were entitled to, the Canadian tax system allows you to correct filed returns. The process is straightforward, and many amendments result in meaningful refunds.
Two Ways to File an Amendment: Online or Paper
Method 1: CRA My Account — "Change My Return" (Recommended)
Log in to CRA My Account at canada.ca/my-cra-account. Go to "Tax returns" → "Change my return". Select the tax year you want to amend, then enter the corrected line amounts directly. No form, no paper, no mailing. The CRA confirms receipt immediately and you can track the status online. Processing typically takes 2 weeks.
Method 2: Form T1-ADJ by Mail
Download Form T1-ADJ from Canada.ca. Complete the form with:
- Your SIN and date of birth
- The tax year you are amending
- Line numbers you want to change
- Original amounts and corrected amounts
- Explanation of each change
Attach all supporting documentation (receipts, amended T4, RRSP contribution receipts, etc.) and mail to your local CRA tax centre. Processing takes 8+ weeks. Always keep copies of everything you mail.
Common Situations Where a T1-ADJ Is Needed
| Situation | What to Fix | Typical Refund Impact |
|---|---|---|
| Missed RRSP deduction | Add Line 20800 amount | 15–33% of contribution amount |
| Missed medical expenses | Add Line 33099/33199 amounts | 15% of eligible amount above threshold |
| Missed charitable donations | Add Line 34900 amounts | 15–33% of donation amount |
| Amended T4 received | Correct Line 10100 and/or Box 22 | Varies — could be refund or additional owing |
| Missed moving expenses | Add Line 21900 expenses | Full deduction at marginal rate |
| Missed tuition carryforward | Add Schedule 11 amounts | 15–20% of tuition amount |
| Capital loss carryback | Apply loss to prior year capital gains | Up to $2,500/year additional refund |
The 3-Year Refund Rule — Critical Deadline
If your amendment results in a refund, you must file it within 3 years from the date of the original Notice of Assessment. After 3 years, the CRA is not obligated to issue a refund — they may still process the amendment but without paying you the overpaid amount.
Example: your 2022 T1 was assessed on May 15, 2023. You have until May 15, 2026 to amend it and receive any refund. If you discover a missed deduction from 2022 in 2027, it is beyond the 3-year window — the amendment can still be filed but the refund may not be paid.
The 10-year general amendment window allows changes but refunds on older years are not guaranteed.
Supporting Documentation: What to Include
Every amendment should include documentation supporting the change. The CRA may request proof before issuing the reassessment. Key documentation by amendment type:
- RRSP contributions: Official RRSP contribution receipts (from the financial institution)
- Medical expenses: Receipts and invoices totaling the claimed amount
- Charitable donations: Official donation receipts from registered charities (CRA number required)
- Moving expenses: Receipts for moving truck, storage, and travel; documentation of new and old addresses and job/school location
- Amended T4: Copy of the corrected T4 slip from your employer
Pro Tip: Review 3 Years of Returns for Missed Deductions
When we review client returns at MaxRefund, we frequently find missed deductions worth $500–$3,000 per year — especially medical expenses (the 3% threshold is misunderstood), charitable donations (not all clients know employer-matched giving counts), and RRSP carry-forwards. Filing T1-ADJ amendments for 3 years can recover thousands of dollars. The CRA refunds with interest for the overpaid period. If you are unsure whether you have been leaving money on the table, a professional review of your last 3 years is often worth far more than it costs.
Frequently Asked Questions
Generally, you can request an amendment going back 10 tax years. For the 2027 filing season, you can amend returns as far back as 2017. However, there is a three-year deadline for requesting a refund — if your amendment results in a refund, you must file within 3 years of the original assessment date to receive it. After 3 years, the CRA may still reassess but is not required to issue a refund.
Form T1-ADJ (T1 Adjustment Request) is the official CRA form to request changes to a filed T1 return. You list the lines you want to change, the original amounts, and the corrected amounts, along with supporting documentation. Alternatively, you can file the same request through CRA My Account using "Change my return" — no paper form needed.
You can add missed deductions (RRSP, union dues, childcare, medical expenses), correct income amounts, add or remove credits (tuition, moving expenses, charitable donations), correct a SIN entry, fix a marital status error, or add a capital loss carryback. You can also remove income you incorrectly reported or correct employment income from an amended T4 slip.
Processing time varies. Amendments submitted online through CRA My Account typically take 2 weeks. Paper T1-ADJ forms take 8 weeks or more. Complex amendments (capital gains, business income, large amounts) may take longer as the CRA may request additional documentation before completing the reassessment.
Yes — filing a T1-ADJ opens your return for review, and the CRA can make changes beyond what you requested. However, this is not common for straightforward amendments. The three-year normal reassessment period limits most CRA changes. If your amendment triggers concerns, the CRA will communicate with you before issuing any unfavorable changes.
Let MaxRefund Amend Your Prior-Year Returns
Our team identifies missed deductions and credits across your filing history, prepares T1-ADJ amendments, and recovers overpaid taxes — often worth thousands.
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