Mistakes can happen when filing your tax return—whether it’s a missed deduction, an incorrect income figure, or a forgotten slip. Fortunately, the Canada Revenue Agency (CRA) provides a structured and accessible process for amending a prior year’s tax return. This guide explains how to identify when an amendment is needed, how to submit the correction, and what to expect during the process.
1. When Should You Amend a Tax Return?
You should amend a previously filed tax return if you realize that you:
- Missed claiming a deduction or credit (e.g., RRSP contribution, tuition, medical expenses)
- Reported income incorrectly or omitted a T-slip (e.g., T4, T5, T3, T4A)
- Overstated a deduction
- Incorrectly claimed an ineligible dependent
- Need to change marital status or spousal/dependent claims
- Forgot capital gains or losses
It is not necessary to amend your return if the CRA has already reassessed it due to your oversight, unless their reassessment was also incorrect.
2. How Long Do You Have to Amend a Return?
The CRA allows you to request an adjustment for up to 10 years from the end of the tax year in question. For example, in 2025, you can request changes going back to the 2015 tax year.
3. Tools for Amending Your Return
You can use the following methods to amend your tax return:
a) CRA My Account – Change My Return
This is the fastest and most recommended method. Through your CRA My Account portal, use the “Change my return” service to submit your correction electronically. You can make changes to tax returns from the past 10 years that have been assessed.
b) ReFILE via Certified Tax Software
If you originally filed online using certified software, you may be able to use the ReFILE service to make changes directly through that platform. However, ReFILE is not available for all types of adjustments, such as changes to marital status or carryforward amounts.
c) Submit Form T1-ADJ (T1 Adjustment Request)
This paper form allows you to explain in detail what you are amending and why. You must include documentation to support the change (e.g., revised T-slip, RRSP receipt, tuition certificate).
- Download from: CRA T1-ADJ
- Mail it to the appropriate tax centre for your region
4. Steps to Amend Using CRA My Account
- Log in to your CRA My Account
- Under “Tax Returns,” select “Change My Return”
- Choose the year you want to adjust
- Enter the corrected information in the appropriate fields
- Submit the adjustment request
Be sure to save or print a copy of your submission for your records.
5. Supporting Documentation
The CRA may request documentation after you submit your amendment. It’s important to keep the following on hand:
- Revised or corrected tax slips (e.g., T4, T5, T3, T4A)
- Receipts for new deductions (e.g., RRSP, charitable donations, medical expenses)
- Proof of tuition or education credits (T2202)
- Details of capital gains or losses
- Letter of explanation (if complex)
6. Common Reasons for CRA to Reject an Adjustment
CRA may deny or delay your amendment request if:
- It falls outside the 10-year window
- Insufficient documentation is provided
- You are trying to amend a year that is currently under audit or review
- The information is already accurate or you’ve already amended it once
7. How Long Does It Take to Process?
The CRA states that processing time for adjustments is:
- 2 weeks if submitted online
- 8–12 weeks if submitted by mail (longer during peak seasons)
You will receive a Notice of Reassessment if your amendment is approved. If it’s denied or altered, you’ll receive a letter with an explanation.
8. Will You Get a Refund (or Owe Money)?
If the amendment results in a reduced tax liability, CRA will issue a refund (including interest if applicable). If it increases your tax owing, you’ll be required to pay the difference, potentially with interest and penalties depending on how late the balance is.
9. Special Considerations for Multiple Year Adjustments
If you’re adjusting several years of tax returns, submit one T1-ADJ per year. Make sure each one is complete and includes all supporting documents. Online changes must also be submitted separately per tax year.
10. Voluntary Disclosures Program (VDP)
If you need to correct a return involving significant errors or omissions (especially if they result in taxes owing), and you want to avoid penalties and prosecution, consider applying through the CRA’s Voluntary Disclosures Program. This is suitable for previously unreported income, offshore assets, or major errors in prior returns.
11. Tips to Avoid Amending in the Future
- Wait until you’ve received all your tax slips (T4s, T5s, T3s, etc.) before filing
- Use auto-fill services in CRA-certified tax software
- Review each return carefully before submission
- Use CRA’s My Account to double-check what they have on file
12. Conclusion
Amending a previous year’s return in Canada is straightforward, especially when done online. Whether you discover an error yourself or receive new tax documents, taking timely action can result in a refund or help you avoid trouble later. Just be sure to use the correct process, include supporting documents, and be patient as the CRA reviews your request.
