How to Amend a Tax Return in Canada: Fixing Mistakes After Filing

Mistakes happen. Maybe you forgot to claim a deduction, received a T4 after you already filed, or realized you entered the wrong number. The good news is that you can fix errors on a filed tax return in Canada without starting from scratch.

The Canada Revenue Agency (CRA) allows you to request changes to a return through a simple amendment process. This guide walks you through exactly how to do it.

Can You Change a Tax Return After Filing?

Yes. You can ask the CRA to change (amend) a tax return that has already been filed and assessed. You cannot simply re-file a new return — you need to submit a formal amendment request.

Important: Wait until your return has been assessed (you have received your Notice of Assessment) before submitting an amendment. Trying to amend before assessment can cause delays.

Common Reasons to Amend a Return

People amend returns for many reasons:

• Received a missing T4, T5, T3, or other slip after filing
• Forgot to claim a deduction (RRSP, childcare, medical expenses, etc.)
• Made a math or data entry error
• Need to correct an address or direct deposit information
• Missed claiming a tax credit
• Employer issued a corrected T4
• Want to carry back a capital loss from a later year
• CRA reassessed and you want to dispute or accept the change

How to Amend a Return: Two Methods

• The CRA offers two ways to amend a filed return:
• Online through CRA My Account (fastest)
• By mail using Form T1-ADJ (Adjustment Request)
• You cannot amend by calling the CRA. Amendments must be submitted in writing or online.

Method 1: Using CRA My Account Online

This is the easiest and fastest method.

• Step 1: Log in to your CRA My Account at canada.ca/my-cra-account.
• Step 2: Under the section for your income taxes, select the tax year you want to change.
• Step 3: Click on the option to request a change to your return.
• Step 4: Select the line(s) you want to change and enter the new amounts.
• Step 5: Provide a brief explanation of why you are making the change.
• Step 6: Submit. The CRA will confirm receipt and process the request.
• Online amendment requests are typically processed within 2 weeks.

Method 2: Sending a T1-ADJ Form by Mail

If you prefer paper or do not have access to CRA My Account, you can mail in a T1-ADJ form.

• Step 1: Download Form T1-ADJ (T1 Adjustment Request) from the CRA website.
• Step 2: Fill out the form with your SIN, the tax year being amended, and the specific line(s) you are changing.
• Step 3: Attach all relevant documents (corrected T4, receipts, etc.).
• Step 4: Write a brief explanation of the reason for the amendment.
• Step 5: Mail the form to your tax centre (the mailing address is on the CRA website).
• Paper amendments typically take 8 weeks or more to process.

What Happens After You Submit the Amendment?

• After you submit an amendment request, the CRA will:
• Send a confirmation that your request was received
• Process the request and either approve the change or ask for more information
• Issue a Notice of Reassessment if the change is approved
• If the reassessment results in a refund, the CRA will issue the refund. If you owe more tax, you will receive a bill.

How Far Back Can You Amend a Return?

Generally, you can request changes to returns from the past 10 years. However, the CRA can only reassess your return within the normal reassessment period, which is typically three years from the date of your original Notice of Assessment.

If you are requesting a refund through an amendment, it is generally available for the past 10 years. There is no time limit to request an amendment that does not result in a refund.

What If the CRA Owes You More Money?

If your amendment results in a lower tax amount than you originally paid, the CRA will issue a refund for the difference plus interest. The CRA pays interest on refunds from the later of: the date you paid the original balance, or the date your return was filed.

What If You Owe the CRA More?

If your amendment results in additional tax owing, the CRA will charge interest from the original due date of the return. This is why it is generally better to amend honestly and promptly rather than leave an error uncorrected.

If you voluntarily disclose an error before the CRA contacts you, you may qualify for the Voluntary Disclosures Program, which can reduce penalties and interest.

Table of Summary

Here is the blog information in 6 easy rows for quick understanding:

Section	Easy Information
1. Topic	The blog explains how to amend a tax return in Canada if you made a mistake after filing.
2. Why Amend	Common reasons include missing T4/T5/T3 slips, forgotten deductions or credits, math errors, address/direct deposit changes, or reassessment disputes.
3. Amendment Methods	Two ways to amend: Online via CRA My Account (fastest) or by mail using Form T1-ADJ. You cannot amend by phone.
4. How to Amend Online	Log in to CRA My Account, select the tax year, request a change, update line(s), explain reason, and submit. Typically processed within 2 weeks.
5. How to Amend by Mail	Complete Form T1-ADJ, attach corrected slips/receipts, provide explanation, mail to CRA tax centre. Processing can take 8 weeks or more.
6. After Submission & Timing	CRA sends confirmation, processes amendment, issues Notice of Reassessment. Refunds include interest; additional tax incurs interest. Generally, you can amend returns from the past 10 years. Prompt voluntary disclosure may reduce penalties.

Frequently Asked Questions

Can I amend a return before the CRA has assessed it?

No. You must wait until your original return has been assessed and you have received your Notice of Assessment before submitting an amendment.

How many times can I amend a return?

There is no limit to the number of times you can amend a return, as long as the request is within the eligible time period.

Can I amend a return that was already reassessed by the CRA?

Yes. If the CRA reassessed your return and you want to make additional changes, you can still submit an amendment request.

What documents do I need to include with my amendment?

Include all supporting documents that justify the change, such as corrected T4 slips, receipts, or updated financial statements.

This is general information only and not professional advice. Consult a professional before acting.