How to Correct a Mistake on Your Canadian Tax Return: T1-ADJ and ReFILE Guide

You filed your tax return, received your Notice of Assessment, and then realized you made a mistake. Maybe you forgot a T4 slip, missed a deduction, or entered the wrong amount on a line. It happens frequently, and the CRA has a straightforward process for fixing it.

This guide explains how to correct your Canadian tax return using the T1 Adjustment Request (T1-ADJ) or CRA's ReFILE service, what the time limits are, and when a correction is not the right approach.

Two Ways to Correct Your Return

Option 1: ReFILE (Online)

ReFILE is the fastest and easiest way to correct a tax return. It is available through certified NETFILE software and through CRA My Account's "Change my return" feature.

How it works:

1. Log in to CRA My Account at canada.ca
2. Go to Tax returns > Change my return
3. Select the tax year you want to correct
4. Enter the line number(s) you want to change, the corrected amounts, and a brief explanation
5. Submit the request electronically

Processing time: Online changes are typically processed within two weeks.

Availability: ReFILE is available for returns from the four most recent tax years that are eligible for NETFILE. For older returns, you need to use the paper T1-ADJ form.

Option 2: T1 Adjustment Request (Paper Form)

The T1-ADJ (Form T1-ADJ E) is a paper form you complete and mail to your CRA tax centre. Use this method if:

• The tax year is too old for ReFILE
• You need to attach supporting documents (receipts, statements, forms)
• You prefer paper correspondence

How to complete it:

1. Download Form T1-ADJ from the CRA website
2. Fill in your personal information and the tax year
3. For each change, enter the line number, the original amount, the revised amount, and the reason for the change
4. Attach any supporting documents
5. Mail it to the tax centre that processed your original return

Processing time: Paper adjustments take eight to twelve weeks to process. During peak periods (March through June), processing times may be longer.

What You Can Correct

Most lines on your tax return can be changed through a T1-ADJ or ReFILE request. Common corrections include:

Income Corrections

Correction	Example
Forgot a T-slip	You received a T4 from a short-term job and did not include it
Wrong employment income	You used the gross amount instead of the box 14 amount
Missing self-employment income	You forgot to report a client payment
Investment income	You missed a T5 slip for bank interest or a T3 slip for mutual fund distributions

Deduction and Credit Corrections

Correction	Example
RRSP contribution not claimed	You made a contribution but forgot to claim it
Medical expenses missed	You found additional medical receipts after filing
Charitable donations	You received a donation receipt after your filing date
Tuition credits	You forgot to claim or transfer tuition amounts
Moving expenses	You moved for work or education and forgot to claim
Self-employment expenses	You found receipts for business expenses you missed
Home office deduction	You did not claim your workspace-in-home costs

Other Corrections

• Changing your marital status
• Updating your province of residence on December 31
• Correcting the number of dependants claimed
• Fixing math errors

What You Cannot Correct via T1-ADJ

Some changes cannot be made through the adjustment process:

• Filing an initial return -- If you did not file for a year, you need to file the return, not adjust it
• Electing or revoking a tax election -- Certain elections (like the principal residence exemption) have their own amendment processes
• Changing how you split pension income -- This requires both spouses to submit adjustment requests
• Foreign tax credit reallocation -- Complex international tax changes may require a Notice of Objection

Time Limits

You can request a T1 adjustment for returns within the 10 most recent calendar years. For example, in 2026, the oldest return you can adjust is your 2016 tax year.

Important deadlines:

• 10-year limit applies to T1-ADJ requests for corrections and additional deductions
• 3-year limit applies to most reassessments the CRA initiates
• 90-day limit applies to filing a Notice of Objection after receiving a Notice of Assessment or Reassessment
• Carryback requests (like carrying a loss back to a previous year) generally have a three-year limit

After 10 years: The CRA has no obligation to process adjustments for returns older than 10 years, though they have discretion to do so in exceptional circumstances through the Taxpayer Relief provisions.

Processing Times and What to Expect

Method	Typical Processing Time	Peak Season (March-June)
ReFILE / Change my return	2 weeks	2-4 weeks
Paper T1-ADJ	8-12 weeks	Up to 16 weeks
With supporting documents	Add 2-4 weeks	Add 4-8 weeks

After the CRA processes your adjustment, they will send you a Notice of Reassessment. This replaces your original Notice of Assessment for that tax year and shows the updated amounts.

Track your request: You can check the status of your adjustment through CRA My Account under "Change my return" or by calling 1-800-959-8281.

Multiple Corrections

You can submit more than one adjustment for the same tax year. Each request is processed independently. If you realize you need to change three things, you can submit them all at once in a single T1-ADJ or ReFILE request, or you can submit them separately.

Best practice: Submit all known corrections in a single request. Multiple separate requests for the same year can cause processing confusion and delays.

T1-ADJ vs. Notice of Objection

These serve different purposes:

	T1 Adjustment (T1-ADJ / ReFILE)	Notice of Objection
Purpose	Correct an error or claim a missed amount	Dispute the CRA's assessment
When to use	You agree with what the CRA assessed but need to change something you filed	You disagree with a change the CRA made to your return
Time limit	10 calendar years	90 days from the Notice of Assessment or Reassessment
Processing	Administrative review	Formal review by CRA Appeals Division
Outcome	Notice of Reassessment	Confirmation, variation, or vacating of the assessment
Escalation	None -- if denied, you may file an objection	Can appeal to Tax Court of Canada

When to file an objection instead:

• The CRA denied a deduction or credit and you believe you are entitled to it
• The CRA added income you believe is incorrect
• You received a Notice of Reassessment that you disagree with
• You already submitted a T1-ADJ and the CRA rejected the change

When to use T1-ADJ instead:

• You forgot to claim a deduction or credit
• You made a data entry error
• You received a T-slip after filing
• You want to add an expense you overlooked

Common Scenarios

"I forgot an RRSP contribution"

Use ReFILE to change line 20800 (RRSP deduction). Have your RRSP contribution receipt handy. The CRA may not require you to submit it with your request, but keep it in case they ask.

"I found more medical expenses"

Use ReFILE to increase your medical expense claim on line 33099 or 33199. The 12-month period you choose for medical expenses does not need to match the calendar year, so make sure any additional receipts fall within the period you originally claimed or adjust the period.

"I did not report a side job"

If you earned income you did not report, submit the correction promptly. The CRA's Voluntary Disclosures Program (VDP) may apply if the amount is significant and you are coming forward before the CRA contacts you. For small amounts, a straightforward T1-ADJ is usually sufficient.

"My employer gave me a corrected T4"

Use ReFILE to update the employment income and tax deducted lines. Attach a note explaining that you received an amended T4.

Tips for a Smooth Correction

1. Correct promptly. The sooner you fix an error, the less interest and penalties accumulate on any additional tax owing.
2. Be specific. In the explanation field, state exactly what changed and why. "Found additional receipt" is better than "correction."
3. Keep copies. Save a copy of your T1-ADJ form or screenshot your ReFILE submission.
4. Watch for the reassessment. After submitting, monitor CRA My Account for the Notice of Reassessment. Review it to confirm the change was applied correctly.
5. Interest implications. If your correction results in additional tax owing, interest runs from the original filing deadline (April 30), not from the date of correction. Correct errors quickly to minimize interest.

Sources

1. CRA: How to change a return
2. CRA: T1 Adjustment Request form (T1-ADJ)
3. CRA: ReFILE -- certified software for electronic changes
4. CRA: Filing a Notice of Objection
5. CRA: Taxpayer Relief provisions -- Cancel or waive penalties and interest