T1 Adjustment Request: When and How to Recover Missed Credits

Every year, thousands of Canadian taxpayers leave money on the table. A medical expense receipt found in a drawer, a work-from-home deduction you did not know existed, or a disability tax credit you assumed you were not eligible for — each of these can mean hundreds or even thousands of dollars in refunds from prior tax years.

The good news: the CRA allows you to adjust previously filed returns going back up to 10 calendar years. This article walks through when to file an adjustment, which method to use, and which credits are most commonly missed.

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 the faster option for most people. It is available through NETFILE-certified tax software and allows you to electronically submit changes for the 2021 through 2025 tax years (as of early 2026). Key details:

• Processing time: Typically two to three weeks
• Availability: Only for returns that were originally filed electronically
• Limitations: Cannot be used for bankruptcy returns, returns for deceased individuals, returns prior to 2021, or to change your address or marital status
• Supported changes: Most income, deduction, and credit adjustments

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

For returns outside the ReFILE window — including anything from 2015 through 2020 — you file a T1 Adjustment Request. This can be done through:

1. CRA My Account: Log in, select "Change my return," and follow the prompts. This method covers the most recent 10 assessed returns.
2. Mail: Complete Form T1-ADJ and mail it to your tax centre along with supporting documents. This is the slowest option but covers the widest range of years.

Paper adjustments typically take 8 to 12 weeks to process. If you are requesting changes to multiple tax years, each year requires a separate adjustment.

The 10-Year Lookback Window

The CRA will generally process adjustment requests for any of the 10 previous calendar years. In early 2026, that means you can adjust returns as far back as 2016. Returns from 2015 and earlier are typically statute-barred and cannot be changed.

There are a few exceptions where the window is shorter or longer:

• 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: In exceptional circumstances (serious illness, natural disaster, CRA error), the CRA may grant relief beyond the normal 10-year window

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 expenses exceeding the lesser of 3% of net income or a fixed threshold (approximately $2,759 for 2025). For lower-income filers, even a modest dental bill can generate a refund.

Work-From-Home Expenses (T2200)

Since the pandemic, many employers have issued T2200 (Declaration of Conditions of Employment) forms allowing employees to claim home office expenses. If your employer required you to work from home and you did not claim the deduction — or if you used the simplified flat-rate method when the detailed method would have yielded more — an adjustment may recover the difference.

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)

The DTC is one of the most under-claimed credits in the Canadian tax system. If you or a dependant has a severe and prolonged impairment in physical or mental function, you may be eligible. The credit is worth approximately $1,700 federally (plus a provincial supplement), and if approved, the CRA often allows you to claim it retroactively for up to 10 years.

Approval requires Form T2201, signed by a qualified medical practitioner. The application process can be lengthy, but the retroactive refund for a decade of missed credits can exceed $15,000.

Climate Action Incentive Payment

Residents of Ontario (and other provinces without their own carbon pricing system) are eligible for the Climate Action Incentive Payment. This is a quarterly benefit based on family size. If you did not receive it because you failed to file a return or did not check the right box, an adjustment to those years can unlock the missed payments.

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 to the tax centre that serves your region (for Ottawa, this is the Sudbury Tax Centre)
4. Allow 8 to 12 weeks for processing

Expected Processing Times

| Method | Typical Processing Time | |---|---| | ReFILE | 2–3 weeks | | CRA My Account | 2–8 weeks | | Mail (T1-ADJ) | 8–12 weeks |

During peak season (March through June), processing times tend to stretch. If you are filing adjustments for multiple years, starting early in the calendar year typically results in faster turnarounds.

When to Work With a Professional

Adjustments involving the disability tax credit, multi-year corrections, or self-employment income revisions require careful documentation. An error in an adjustment request can trigger a review of the entire tax year, which may result in the CRA examining items beyond the scope of your original change.

Our tax situations services include a full review of up to 10 prior years to identify missed credits. For many clients, the refunds recovered on past returns more than cover the cost of professional preparation — and they start fresh with a complete, optimized filing history.

If you suspect you have missed credits on prior returns, the first step is a review.