T1 Adjustment: How to Fix a Tax Return You Already Filed

On this page

• Three Ways to Change a Filed Return, and Which One to Use
• Change My Return in CRA My Account, Step by Step
• ReFILE Through Your Tax Software: Limits and Restrictions
• Filing Form T1-ADJ by Mail: When It Is Your Only Option
• How Far Back You Can Go: The 10 Year Limit
• What to Attach So Your Request Is Not Rejected
• How Long a T1 Adjustment Takes to Process
• What Happens Next: Reassessment, Refund, Interest or a Balance Owing
• When to File an Objection Instead of an Adjustment
• FAQ: Changing a Canadian Tax Return After Filing
• Found a Mistake in a Past Return? Have Us Review It First

Three Ways to Change a Filed Return, and Which One to Use

You filed, you got your notice of assessment, and then a T3 slip showed up in the mail. Or you realised you never claimed the tuition. Or your accountant spotted that you have been missing the medical expenses for three years running.

Good news: you do not refile the return. You request an adjustment, and CRA reassesses.

The short answer on which method to use:

Situation	Use this
2016 or later, straightforward change, you have a CRA account	Change my return in CRA My Account. Two weeks.
2021 or later and you still have the return open in your tax software	ReFILE. Two weeks.
Older years, bankruptcy years, wrong province, non resident, or the online options are blocked	Form T1-ADJ by mail. About 16 weeks.
CRA already changed your return and you disagree with the change	Notice of objection, not an adjustment. Different form, hard deadline.

You can go back 10 calendar years for a refund. Beyond that CRA will not issue money back, no matter how valid the claim.

Now the detail.

 

All three do the same thing: they ask CRA to reassess a year you already filed. They differ in speed and in what they will accept.

	Change my return	ReFILE	T1-ADJ by mail
Where	CRA My Account, online	Your certified tax software	Paper, mailed to your tax centre
Years available	2016 onward	2021 onward	Any year within the 10 year window
Typical processing	2 weeks	2 weeks	16 weeks
Attachments	Uploaded if CRA asks	Not submitted with the request	Mailed with the form
Best for	Most people, most situations	Multiple line changes at once	Anything the online options refuse

Rule of thumb: try online first. The paper route is eight times slower and there is no prize for using it.

 

Change My Return in CRA My Account, Step by Step

This is the default option and it handles the large majority of adjustments.

1. Sign in to CRA My Account.
2. Open Change my return from the menu.
3. Pick the tax year you want to change.
4. Enter the line number you are changing and the revised amount. If you are adding a slip you never reported, you enter the line the slip belongs to, not the slip itself.
5. Review the summary CRA generates, then submit.
6. Watch for a message in My Account. If CRA wants documentation, it will ask, and you upload it through Submit documents.

When it will not work. Change my return is blocked if:

• The year is 2015 or earlier
• It is a bankruptcy return, or a return for the year before bankruptcy
• It is an optional or elective return for someone who has died
• The original return was filed for the wrong province or territory of residence
• You are a non resident, or the return involves certain international elements
• There is already an adjustment in progress for that year

If any of those apply, skip to the T1-ADJ section.

 

ReFILE Through Your Tax Software: Limits and Restrictions

ReFILE lets you make the correction inside the same software you filed with and transmit it electronically. If you changed several things at once, this is usually the tidiest route, because the software recalculates everything downstream for you.

What ReFILE will not do:

• Tax years before 2021
• Bankruptcy returns
• Optional returns for a deceased person
• Returns filed under the wrong province or territory
• Non resident returns
• Any return that needs Form T2203 (income allocated to multiple jurisdictions)
• Change your marital status, direct deposit details, address, or your election to contribute to the Elections Canada list. Those are handled separately in My Account.

One practical warning: some software will happily let you ReFILE a return it has since updated to a newer version of the forms. Reopen the return, confirm the figures still match your original assessment, then make the one change you actually intend.

 

Filing Form T1-ADJ by Mail: When It Is Your Only Option

Form T1-ADJ, T1 Adjustment Request, is the paper fallback. Fill it in with:

• Your name, address, SIN and daytime phone number
• The tax year being changed
• For each change: the line number, the amount as previously reported, the amount it should be, and the difference
• A short plain language explanation of why

Then mail it, with supporting documents, to your tax centre. A letter works too if you do not have the form handy, as long as it contains the same information, but the form is less likely to be misread.

Two things that speed it up dramatically:

• One envelope per tax year. Do not bundle four years into one package. Send four separate requests.
• Number your attachments and reference them in the explanation, so the assessor can match a receipt to a line without hunting.

 

How Far Back You Can Go: The 10 Year Limit

You can request an adjustment for any of the previous 10 calendar years. In 2026 that means 2016 through 2025.

A few nuances worth knowing:

• The 10 year window is a refund limit. CRA can reassess you to collect more tax outside that window in cases of misrepresentation, neglect or fraud.
• Requests for older years fall under the taxpayer relief provisions, which are discretionary. CRA can decline.
• If you are fixing something that means you owe money rather than get money back, and it is more than a year overdue, look at the Voluntary Disclosures Program first. Applying under the VDP before CRA contacts you can get penalties waived and part of the interest relieved. Filing a plain adjustment does not.

That last point matters more than most people realise. There is a real difference between walking in voluntarily and being caught.

 

What to Attach So Your Request Is Not Rejected

The most common reason an adjustment gets denied is not that the claim was wrong. It is that the proof was thin.

Claim	What to send
Missed T slip	Copy of the slip
Medical expenses	Receipts and a summary total, plus the pharmacy printout if it is prescriptions
Charitable donations	Official donation receipts with the charity’s registration number
Tuition	T2202 from the institution
RRSP contribution	Official contribution receipt
Employment expenses	Signed T2200, plus the T777 and receipts
Moving expenses	T1-M with receipts, distance calculation, proof of the new work location
Support payments	Court order or written agreement, and proof of payment
Rental or business change	Revised T776 or T2125, plus the underlying records

Send complete documentation for the whole amount claimed, not just the part you are adding. If you originally claimed $3,000 of medical and you are now claiming $4,500, CRA wants receipts for the full $4,500.

Keep originals. Send copies.

 

How Long a T1 Adjustment Takes to Process

Method	CRA’s stated service standard
Change my return (online)	About 2 weeks
ReFILE	About 2 weeks
T1-ADJ by mail	About 16 weeks
Complex cases	Up to 33 weeks

“Complex” covers more than you might expect: several years at once, loss or credit carrybacks to prior years, returns for a deceased person, anything requiring a manual review or a referral to another CRA area.

Filing season also matters. An adjustment submitted in late March sits behind millions of returns. The same request in September moves noticeably faster.

 

What Happens Next: Reassessment, Refund, Interest or a Balance Owing

When CRA finishes, you get a notice of reassessment showing what changed and why.

• If you are owed money, CRA pays it by direct deposit or cheque, and pays you refund interest if the delay was long enough. Refund interest is taxable income in the year you receive it, so it shows up on next year’s return.
• If you now owe, interest is charged from the original balance due date for that year, not from the date of the reassessment. This is why fixing an old under reported year gets more expensive the longer you wait.
• If CRA disagrees with part of it, the reassessment will say so in the explanation of changes. At that point you can supply more documentation, or object.
• Knock on effects. Changing one year can cascade: RRSP room, tuition carryforward, capital loss carryforward, GST/HST credit and Canada Child Benefit entitlements. CRA usually recalculates benefit entitlements automatically, but not always immediately.

 

When to File an Objection Instead of an Adjustment

The distinction is simple once you see it:

• You made the mistake → adjustment request.
• CRA made a change you disagree with → notice of objection.

An objection is filed on Form T400A or through Register my formal dispute in My Account, and there is a hard deadline. For individuals it is the later of:

• 90 days after the date on the notice of assessment or reassessment, or
• one year after the filing due date for that return

Miss it and you need an extension application, which is discretionary and not always granted.

Practical advice: if you are unsure, send the adjustment request and protect the deadline by objecting if the 90 days is running out. An objection can be withdrawn. A missed deadline cannot be undone.

Maxpro Financials reviews prior year returns for missed claims before filing anything, so an adjustment request goes in once, complete, rather than three times in pieces.

 

FAQ: Changing a Canadian Tax Return After Filing

Can I just file the return again to fix it? No. Filing a second return for the same year creates a duplicate and slows everything down. Use an adjustment.

How many years can I adjust at once? As many as you like within the 10 year window, but submit each year as a separate request.

Will a T1 adjustment trigger an audit? An adjustment is not an audit flag by itself. A large or unusual claim with no documentation attached is more likely to attract a review, which is why the attachments matter.

I forgot to claim an RRSP contribution. Do I have to adjust? You must report the contribution in the year it was made, but you can carry the deduction forward. If you reported it and simply did not deduct it, no adjustment is needed. If you never reported it at all, adjust that year.

Can my accountant file the adjustment for me? Yes, through Represent a Client, and it is usually faster because they can see your account and confirm the reassessment went through.

What if the adjustment means I owe money? Interest runs from the original due date. If it is an older year and you are coming forward voluntarily, look at the Voluntary Disclosures Program before you file the adjustment.

How do I check the status of my request? Change my return and ReFILE requests show a status in My Account. Mailed T1-ADJ requests generally do not show up until the reassessment is issued.

Can I adjust a return for someone who has died? Yes, but the online options are restricted and you will usually need the paper T1-ADJ, plus proof you are the legal representative.

Does an adjustment change my benefit payments? It can. Canada Child Benefit, GST/HST credit and provincial credits are all based on assessed income, so a change to income recalculates them, sometimes retroactively.

Is there a fee to file a T1 adjustment? CRA charges nothing. If you use a professional, you pay for their time, which is usually worth it when the claim is large or documentation heavy.

 

Found a Mistake in a Past Return? Have Us Review It First

Before you send anything to CRA, it is worth having someone look at the whole year rather than the one line that caught your attention. In practice, a return with one missed slip usually has a missed credit sitting next to it, and a single well documented adjustment beats three separate requests spread over eight months.

Maxpro Financials reviews prior year returns for individuals and owner managed businesses across BC and Alberta, prepares and files the adjustment, and handles the follow up if CRA asks for documentation. If the year in question involves an amount you owe rather than a refund, we will tell you plainly whether a Voluntary Disclosures application is the better route before anything gets filed.

Book a consultation or call BC +1 (778) 951 1269 / Alberta +1 (403) 437 6016.