How to Fix a Filed Canadian Tax Return: T1-ADJ, ReFILE & the 10-Year Window

The April 30 filing rush often means some deductions, credits, or slips get missed. The good news: you do not need to refile your return to fix it. CRA gives you up to 10 years to adjust a previously filed T1, and for most errors the fix takes less than 10 minutes through CRA My Account.

Here is exactly how the adjustment system works, which method to use when, and the mistakes that are worth going back to fix. Before requesting any adjustment, you need your Notice of Assessment — CRA will reject any adjustment filed before the original return has been assessed.

Three Ways to Adjust a Return

Canadians have three options depending on how recent the year is and how the return was originally filed.

Method	How	Years Covered	Typical Processing
ReFILE (via NETFILE software)	Re-submit through your tax software	3 most recent years	2–4 weeks online
Change my return (CRA My Account)	Online form	Current year + 9 prior = 10 years	2 weeks online
Form T1-ADJ (paper)	Mail to CRA tax centre	Current year + 9 prior = 10 years	8–12 weeks

For almost all filers, ReFILE or Change my return through My Account is faster, cheaper, and easier than the paper T1-ADJ. Paper is only necessary if you cannot access My Account or if your adjustment involves supporting documents CRA needs to see before reassessing.

ReFILE: Re-Submit Through Tax Software

If you filed via NETFILE and the year in question is one of the three most recent tax years, you can ReFILE — your software re-transmits a corrected return directly to CRA.

How it works:

1. Open the original return in your tax software
2. Make the corrections (add missed slip, adjust deduction, correct credit)
3. Select “ReFILE” instead of “NETFILE”
4. Software generates a new confirmation number

Limits:

• Only works for the 3 most recent years
• Only works if the original was NETFILE-ed (not paper-filed)
• Some situations cannot ReFILE — for example, changing your marital status mid-year, changing direct deposit info, or if CRA has flagged the return for review

ReFILE is usually processed in 2–4 weeks, and if you’re owed a refund it’s direct-deposited to the account CRA has on file.

Change My Return (CRA My Account)

For any of the 10 most recent tax years, you can submit an online adjustment request through CRA My Account → Tax returns → Change my return.

How it works:

1. Log into My Account at canada.ca
2. Navigate to Tax returns → Change my return
3. Select the year you want to adjust
4. Choose the line number affected (e.g., Line 23200 for RRSP, Line 33099 for medical)
5. Enter the corrected amount
6. Attach supporting documents if required
7. Submit

Most adjustments require no documentation upload — CRA will request receipts if they need to verify. Processing is typically 2 weeks for simple adjustments (missed slip, added deduction) and longer if CRA requests documentation.

Situations where Change my return does not work:

• Bankruptcy returns
• Returns for a deceased person
• Non-resident returns
• Returns still being processed (wait for Notice of Assessment first)

Form T1-ADJ (Paper)

The paper T1-ADJ form is the fallback when My Account is not accessible or the situation is too complex for the online form.

• Download from canada.ca, complete by hand or with a tax professional
• Mail to the CRA tax centre serving your province (address on the form)
• Processing time is 8–12 weeks, sometimes longer during tax season

Paper T1-ADJ is also the correct method for most legal or estate-driven changes (e.g., capital gains adjustments after a will dispute, or corrections to a deceased-person return by an executor).

Common Adjustments Worth Making

Not every tiny correction is worth the trouble of an adjustment. These are the ones that typically produce a refund large enough to justify 10 minutes in My Account.

Missed RRSP Contribution (First 60 Days)

If you contributed to your RRSP between January 1 and March 3, 2026 but forgot to claim it on your 2025 return, an adjustment recovers the deduction. A $5,000 missed contribution at a 30% marginal rate is worth about $1,500.

Line affected: 23200 (RRSP deduction) via Schedule 7.

Forgotten Medical Expenses

Medical expense receipts discovered after filing — especially for the lower-income spouse, who has a lower 3%-of-net-income threshold — are worth claiming retroactively. The medical credit covers any 12-month period ending in the tax year, so overlapping windows between adjacent years can matter.

Line affected: 33099 (medical expenses).

Missed Charitable Donations (Including Prior-Year Carryforwards)

Donations made in 2025 but forgotten, or carryforward balances from 2020–2024 that were never claimed, can be added via adjustment. The federal credit jumps from 15% to 33% on donations above $200 per year, so combining multiple years’ donations into one claim often maximizes the refund.

Line affected: 34900 (charitable donations).

Tuition Tax Credit Forgot to Transfer

Students whose tuition credit exceeds their own tax owing can transfer up to $5,000 to a spouse, parent, or grandparent each year. If the student forgot to file Schedule 11 or forgot to designate the transfer on the T2202, an adjustment fixes it — on either the student’s or the recipient’s return.

Line affected: 32300 (tuition and education) on the student’s return; 32400 on the recipient’s return.

Missed T-Slips Found After Filing

If an issuer sends a late T4, T5, or T3 after you have already filed, you do not need to wait for CRA to reassess — submit the adjustment yourself through My Account. Doing it proactively avoids any implication of deliberate omission.

Capital Loss Carryback

Net capital losses realized in 2025 can be carried back to any of the 3 prior years (2022, 2023, or 2024) to recover taxes paid on capital gains in those years. This requires filing Schedule 3 amendments for the prior year via T1-ADJ, since ReFILE typically cannot handle carryback logic.

Line affected: Net capital loss carried back (Form T1A).

Disability Tax Credit (DTC) Approved Retroactively

When someone is approved for the Disability Tax Credit mid-year or retroactively, CRA can reassess up to 10 prior years of returns to apply the credit. This is the single biggest retroactive refund most Canadians will ever encounter — often $10,000–$40,000 when combined with the refundable Canada Workers Benefit enhancement and Canada Caregiver Credit for a supporting family member.

Line affected: 31600 (DTC for self) or 31800 (DTC for dependant).

Adjustments That Are NOT Worth It

Some corrections produce a reassessment too small to justify the effort or — worse — end up costing you more than the refund in interest and review risk.

• Very small missed deductions (< $50 net refund after processing time)
• Rounding errors on slips that already matched CRA’s records
• Late-discovered errors on returns older than 10 years — CRA will not accept these regardless of what the mistake was
• Anything that increases your balance owing by less than the interest you would pay — let CRA reassess you organically rather than volunteering a small adjustment

Interest and Refunds on Adjustments

When CRA reassesses a return in your favour:

• Refund interest is paid on any overpayment starting 30 days after the later of (a) the original filing deadline or (b) the date you actually filed
• The rate is CRA’s prescribed refund interest rate, which is the Treasury Bill rate + 2% (currently around 6% annualized)
• Refunds go to whatever direct deposit account CRA has on file — see refund processing times by filing method for what to expect and how to track status

When CRA reassesses against you (you owe more):

• Arrears interest is charged at the Treasury Bill rate + 4% (currently around 8% annualized) from the original filing deadline
• A 10% repeated-error penalty can apply if CRA has already reassessed the same type of mistake in your recent history

The 10-Year Fairness Provision

Many filers do not realize that CRA has a 10-year taxpayer relief window codified in the Income Tax Act. For any tax year ending in the last 10 calendar years, you can request adjustments — even if the mistake was your own. Beyond 10 years, CRA has no statutory authority to change the assessment.

The window is calculated from the end of the tax year, not from the filing date. So on April 21, 2026:

• 2016 tax year adjustments must be submitted by December 31, 2026
• 2015 tax year and earlier are closed permanently

If you realize a multi-year mistake (e.g., the Disability Tax Credit was never claimed for a family member who qualified years ago), prioritize the oldest year first — the clock is moving against you.

When to Use a Tax Professional

Most straightforward adjustments (missed slips, RRSP top-ups, medical receipts, donation carryforwards) can be handled by yourself in My Account in under 10 minutes. Consider professional help when:

• The adjustment involves capital loss carrybacks or forward to multiple years
• The Disability Tax Credit is being applied retroactively across many years
• The original return involved a business (T2125), rental property (Form T776), or foreign income — adjustments here often cascade into other forms
• CRA has already reassessed against you and you are disputing that reassessment

The cost of a tax professional to handle a multi-year DTC retroactive adjustment is usually 5–10% of the recovered refund — a bargain given the complexity.

Bottom Line

Filed your 2025 T1 and found a problem afterward? You have up to 10 years to fix it, and for most mistakes the fix takes 10 minutes via CRA My Account → Change my return. ReFILE through your tax software works for the 3 most recent years. Paper T1-ADJ is the fallback for everything else.

Do not panic. Do not refile from scratch. Use the adjustment system.

If you have not filed at all yet and the deadline has passed, fix that first — see missed the April 30 deadline — then use this adjustment guide for any corrections you discover after CRA assesses the late return.