To amend a tax return in Canada, wait until you’ve received your Notice of Assessment, then submit the correction one of three ways: the Change My Return feature in your CRA My Account, the ReFILE service inside certified tax software, or a paper T1 Adjustment Request (T1-ADJ) mailed to your tax centre. Under subsection 152(4.2) of the Income Tax Act, you have up to ten calendar years after the end of the tax year to ask for a refund or a reduction in tax owing. The mechanics are simple. The consequences for interest, benefits, and your appeal rights are where people get tripped up.
Wait for Your Notice of Assessment First
You can’t submit changes to a return the CRA hasn’t finished processing. Until the Notice of Assessment lands, there’s no baseline for the agency to compare your corrections against, and trying to push an adjustment through early creates conflicts that delay everything. Once the assessment arrives, you’re free to file the correction.
The outer deadline is ten calendar years from the end of the taxation year. A 2016 return, for example, can be adjusted until December 31, 2026. After that, the CRA no longer has authority to issue a refund or reduce tax for that year, even if the error is plain. The ten-year limit applies to individuals and graduated rate estates, not to trusts.
The Three Ways to File the Change
Change My Return
The fastest route is Change My Return, inside CRA My Account. Pick the tax year, enter the updated amounts on the affected lines, and submit. It covers any of the ten previous calendar years. You receive a confirmation number, and processing typically takes about two weeks.
ReFILE Through Certified Tax Software
If you filed your original return electronically using certified tax software, you can send an amended return through ReFILE from within that software. You don’t have to use the same product you filed with originally, though it’s usually easier. ReFILE is available for the 2021 tax year and later. The service runs daily except between 3 a.m. and 6 a.m. Eastern for maintenance, and it shuts down from February 2 to 23, 2026, for annual tax-year updates. The software gives you a timestamped acknowledgment once the transmission goes through.
Paper T1 Adjustment Request
The T1-ADJ is a downloadable PDF. For each line you’re changing, enter the original amount, the amount of the change, and the revised total. Attach supporting documents, add a short explanation for each change, and mail everything to the tax centre for your region. Paper requests take roughly eight weeks. Tracked mail is worth the small extra cost, because the CRA has no record of your submission until the envelope is opened.
When Paper Is Your Only Option
The digital tools don’t cover everything. You need to use the paper T1-ADJ if:
- You’re changing a return for the year you went bankrupt, or any earlier year.
- The original return was filed under the wrong province or territory of residence.
- You need to file or amend Form T2203 for business income earned in more than one province.
- You’re adjusting a return filed for someone who has died, including any optional returns.
- The return is an emigrant, deemed resident, section 115 non-resident, or similar cross-border filing.
The online portals will flag these situations or simply refuse the request. Don’t fight the tool. Go straight to paper.
What to Put in the Request
Every adjustment, no matter how you submit it, needs the same core elements: your Social Insurance Number, the tax year being changed, and the specific line numbers affected. Line numbers tell the CRA exactly where the return needs updating and keep your request from getting bounced between reviewers.
For each line, show the original amount you reported, the dollar change, and the corrected total. Write a short explanation. Something like “received corrected T4 from employer” or “forgot to claim transit pass” is enough. Reviewing officers read dozens of these a day. Clarity beats length.
Supporting documents are your proof: corrected T4s, medical receipts, tuition statements, donation receipts, anything backing the new numbers. For paper submissions, send copies organized in the same order as your line changes. For digital submissions, the CRA may still ask you to upload or mail documents separately if they want to verify a claim.
What Happens After You Submit
When the review is done, the CRA issues a Notice of Reassessment. It replaces the previous assessment and lays the revised calculations next to the old ones. If the change increases your refund, the additional amount is direct-deposited or mailed. If it reduces your refund or creates a balance owing, the notice states what you owe and when.
Online submissions generally produce a Notice of Reassessment within two weeks. Paper takes about eight weeks from the day the CRA receives the envelope. The notice also flags anything the CRA changed from what you asked for. They aren’t obligated to accept every line item as submitted.
Interest If Your Change Means You Owe More
If the correction shows you underpaid, interest on the additional tax runs from the original balance-due date for that year, not from the date you filed the adjustment. Under section 161 of the Income Tax Act, the CRA charges compound daily interest at the prescribed rate. For the first two quarters of 2026, that rate is 7% annually.
This is where old-year corrections hurt. Fixing a return from several years back that turns out to increase your tax means interest has been compounding the whole time. Coming forward voluntarily through a standard adjustment doesn’t earn you a grace period. The interest accrues either way.
If the mistake involves unreported income and could trigger penalties on top of interest, the Voluntary Disclosures Program may offer partial relief, provided the disclosure is voluntary, complete, involves penalties or interest, relates to information at least one year past its filing deadline, and includes payment or a payment arrangement. A standard T1 adjustment handles honest mistakes. The VDP is for situations where penalties are in play.
How the Change Affects Your Benefits
An adjustment that changes your net income flows into any benefit calculation that depends on that figure. The Canada Child Benefit is recalculated whenever a reassessment of your return or your spouse’s return affects the benefit. The CRA sends a new CCB notice with revised amounts. If you were underpaid, the difference is added to your next payment. If you were overpaid, the CRA recovers the excess.
The GST/HST credit works the same way. A reassessment that changes adjusted family net income triggers a notice of redetermination with the revised amount, and any shortfall goes out with the next quarterly payment. One thing the adjustment process cannot do is start a new benefit or credit you never claimed on the original return. That takes a separate application.
If You Disagree With the Reassessment
If the Notice of Reassessment doesn’t match what you asked for, whether the CRA disallowed a deduction or altered a figure you believe is correct, you can formally object. You file a Notice of Objection using Form T400A or the “Register a formal dispute” feature in CRA My Account.
For individuals, the deadline is the later of one year after your filing due date for that tax year, or 90 days after the date on the Notice of Reassessment. If you miss it, you can apply for an extension up to one year after the objection deadline, but approval isn’t guaranteed.
Filing an objection does not pause your obligation to pay the balance shown on the reassessment. If you lose, interest has been accumulating the whole time. If you win, the CRA refunds the overpayment with interest. The objection is a separate track from an adjustment: it’s adversarial, handled by a CRA appeals officer, and can escalate to the Tax Court of Canada if it isn’t resolved in your favour.