How to Change a Tax Return: T1 Adjustments and ReFILE

An assessed tax return is not always final. If a late slip arrives, a medical receipt was missed, or a disability tax credit is approved, the return can often be corrected. The result may be a refund, a lower balance, or simply an accurate tax record.

The CRA generally considers changes for the previous 10 calendar years. Here is the clean comparison of Change my return, ReFILE, and Form T1-ADJ, including the current years and 2026 service targets.

T1-ADJ vs. CRA ReFILE: Which to Use

There are two primary ways to request a change to a previously assessed T1 return.

CRA ReFILE (Online)

ReFILE is available through CRA-certified NETFILE software. During the 2026 filing program, it accepts amended 2022, 2023, 2024, and 2025 T1 returns. Key details:

• Processing time: The CRA processes most electronic adjustment requests within two weeks
• Availability: Only for returns that were originally filed electronically
• Limitations: ReFILE has exclusions, including some bankruptcy and deceased-person returns, and it cannot change personal information such as an address or marital status
• Supported changes: Most income, deduction, and credit adjustments

T1-ADJ (Form T1-ADJ / Paper or My Account)

For years outside the ReFILE window, or changes that ReFILE does not support, use one of these options:

1. CRA My Account: Select "Change my return" and follow the prompts for an eligible assessed return.
2. Mail: Complete Form T1-ADJ and send it to the CRA with supporting documents that have not already been provided.

The CRA's current service standard for paper adjustment requests is eight weeks. Complex requests can take much longer. If you are changing multiple tax years, provide a clear calculation and documents for each year.

The 10-Year Lookback Window

In 2026, a request generally must relate to the 2016 tax year or later. The available online method can cover fewer years than the overall 10-year limit.

Different requests can have their own rules and time limits:

• Loss carrybacks: If you are requesting a carryback of a loss to a prior year, specific rules apply depending on the type of loss
• Voluntary Disclosures Program (VDP): If you failed to report income and want to come forward, the VDP has its own rules and timelines
• Taxpayer relief provisions: Requests to cancel or waive penalties and interest follow separate criteria and a 10-year limitation period

Commonly Missed Credits and Deductions

These are the adjustments we file most frequently for Ottawa clients.

Medical Expenses

You can claim eligible medical expenses for any 12-month period ending in the tax year, provided the expenses were not claimed in a prior year. Commonly missed items include:

• Dental work not covered by insurance
• Prescription eyeglasses and contact lenses
• Fertility treatments
• Travel expenses to receive medical treatment (more than 40 km from home)
• Premiums for private health insurance plans

The federal medical expense tax credit applies to eligible expenses above the lesser of three percent of net income and the annual CRA threshold. The result depends on the claim period, income, reimbursements, and who claims the family expenses.

Work-From-Home Expenses (T2200)

Employees who met the conditions for a prior year may be able to add eligible home-office expenses supported by Form T2200. The temporary flat-rate method only applied to certain earlier tax years, so use the rules for the year being changed.

The detailed method allows claims for a proportionate share of rent, electricity, heating, internet, and maintenance costs based on the size and use of your home office space.

Disability Tax Credit (DTC)

If you or a dependant has a severe and prolonged impairment in physical or mental function, the Disability Tax Credit may apply. The amount varies by tax year and province. If the CRA approves eligibility for prior years, those returns may be reassessed within the permitted period.

Approval requires Form T2201, with the relevant sections completed by a qualified medical practitioner. Do not estimate a refund before the CRA confirms the eligible years and the effect on each return.

Past Canada Carbon Rebate Amounts

The Canada Carbon Rebate, formerly the Climate Action Incentive payment, is closed. There are no regular quarterly payments after April 2025. The CRA says an eligible person who has not filed a return for 2021 through 2024 may still receive the applicable past amount after that return is assessed. Check the current CRA rules before relying on an adjustment for a past payment.

Northern Residents Deduction

If you lived in a prescribed northern zone (including parts of Northern Ontario) for at least six consecutive months, you may be eligible for the northern residents deduction. This includes a residency amount and a travel benefit. Ottawa itself is not in a prescribed zone, but if you previously lived in one and did not claim the deduction, an adjustment is warranted.

Step-by-Step: Filing a T1 Adjustment

Through CRA My Account

1. Log in to your CRA My Account at canada.ca/my-cra-account
2. Select "Change my return" from the menu
3. Choose the tax year you want to adjust
4. Select the line number you want to change (e.g., Line 33099 for medical expenses)
5. Enter the corrected amount and provide a brief explanation
6. Submit and note the confirmation number

Through ReFILE

1. Open the tax return for the relevant year in your NETFILE-certified software
2. Make the changes to the applicable fields
3. Use the ReFILE function to transmit the amended return
4. The CRA will process the change and issue a revised Notice of Assessment

By Mail

1. Complete Form T1-ADJ, available on the CRA website
2. Attach supporting documents (receipts, T-slips, T2200, T2201, etc.)
3. Mail it to the tax centre shown in the current CRA instructions
4. Keep a copy of the package and proof of mailing

Expected Processing Times

Complex requests and requests selected for review can take longer. Use the CRA progress tracker or your account rather than assuming a request is complete when the target time passes.

Correct the Record with Confidence

Adjustments involving the disability tax credit, multiple years, or self-employment income need a clear calculation and supporting records. A professional can also check whether a change affects benefits, carryforwards, or another tax year.

Our tax situations services include prior-year reviews and adjustment preparation. For a simpler return, the software or accountant guide can help you decide how much support you need.

If you suspect a prior return missed something, start with a careful review of the expected tax effect and supporting evidence.