How to fix a tax return in Canada: changes, objections, appeals and taxpayer relief

If you made a mistake on a return, you can ask the CRA to change it once you have your notice of assessment, using Change my return in My Account, ReFILE through certified software or Form T1-ADJ, generally for any of the 10 previous calendar years. If instead you disagree with the CRA's assessment, you must file a notice of objection within 90 days of the date on the notice (or within one year after the filing deadline, whichever is later), or you can lose the right to appeal. Separate taxpayer relief requests (Form RC4288) can cancel penalties and interest caused by circumstances beyond your control, also within 10 years.

This guide sits in the mistakes and sources hub. It is general information, not legal or tax advice; objections and appeals with significant amounts at stake are worth discussing with a tax professional or lawyer.

Choose the right route

Your situation	Route	Time limit
You forgot a slip, a receipt or a credit	Change my return / ReFILE / T1-ADJ	Generally the 10 previous years (refunds for older years are at the CRA's discretion)
The CRA sent a letter asking for receipts (review)	Reply to the review with documents	By the date in the letter, usually about 30 days
You disagree with an assessment or reassessment	Notice of objection (Form T400A or online)	90 days from the date of the notice, or one year after the filing deadline, if later
You missed the objection deadline	Application for an extension	Within one year after the objection deadline, with reasons
You disagree with the CRA's decision on the objection	Appeal to the Tax Court of Canada	90 days after the decision (or after 90 days without a decision)
Penalties or interest because of illness, disaster, CRA delay, or inability to pay	Taxpayer relief request (RC4288)	10 calendar years from the end of the year concerned
Service problems with the CRA (delays, rudeness, wrong information)	CRA service complaint, then the Taxpayers' Ombudsperson	After trying the CRA's process

Changing a return you already filed

Wait until you receive the notice of assessment for the original return. Then:

Change my return in CRA My Account: enter the line numbers and new amounts. Best for most corrections.
ReFILE through the certified software you used, for recent years.
Form T1-ADJ by mail, with supporting documents.

Do not file a second complete return for the same year; it will be treated as a duplicate and delay things. Corrections that increase your tax are best made voluntarily and promptly; the CRA can reassess within the normal reassessment period (generally three years after the date of the original notice of assessment for individuals) and, in cases of misrepresentation due to neglect, carelessness or wilful default, beyond it.

Worked example (illustrative): in March 2027 Maria finds $2,400 of dental receipts from 2025 that she forgot to claim. Her 2025 net income was $55,000, so the medical threshold is 3% × $55,000 = $1,650 (less than the 2025 dollar threshold of $2,834). She had already claimed other medical expenses above that threshold, so the whole $2,400 is eligible; at the 2025 federal credit rate of 14.5%, it is worth about $348 federally, plus the provincial credit. She uses Change my return; the CRA issues a notice of reassessment and refunds the difference with any applicable refund interest.

Objecting to an assessment

A notice of objection asks the CRA's Appeals Branch, which is separate from the officers who made the assessment, to review it.

File online in My Account (Register a formal dispute) or with Form T400A.
State the facts and reasons, the amounts in dispute and attach documents.
Collection of most amounts under objection on an income tax assessment is generally paused while the objection is pending, but interest continues on any amount you finally owe, so some people pay and object.
The Appeals officer can confirm, vary or vacate the assessment. You receive a decision letter.

If the Appeals Branch does not resolve the dispute, you can appeal to the Tax Court of Canada. The informal procedure (for appeals where the federal tax and penalties in issue total $25,000 or less for a year, or a loss in issue of $50,000 or less, under section 18 of the Tax Court of Canada Act) is simpler, has fixed rules on costs and lets you represent yourself. Larger disputes use the general procedure, where a lawyer is strongly advisable.

Review letters are not reassessments

The CRA routinely reviews returns before or after assessment and asks for proof of claims such as child care, medical expenses, moving expenses, donations, tuition or the home buyers' amount. A review letter:

Gives a deadline (often 30 days) and lists the documents wanted.
Is answered by uploading documents in My Account ("Submit documents") with the case or reference number.
If ignored, usually leads to the claim being denied and a reassessment.

Keeping receipts organized by year, as in the tax return checklist, makes reviews quick.

Taxpayer relief: penalties and interest

The CRA can cancel or waive penalties and interest, and in limited cases accept late elections, if the problem was caused by:

Extraordinary circumstances beyond your control: serious illness or accident, death of an immediate family member, natural or human-made disasters, civil disturbance or disruption of services.
Actions of the CRA: processing delays, incorrect information from the CRA, errors in CRA material.
Inability to pay or financial hardship, mainly for interest.

Use Form RC4288 or My Account, explain the timeline and attach evidence. If refused, you can ask for a second review, and then for a judicial review in the Federal Court. Relief is not a route to dispute the tax itself; that is what objections are for. See late-filing penalties.

Quebec

Quebec residents correct their TP-1 with Revenu Québec separately, using its online services or the form for requesting an adjustment, and object to a Quebec assessment with Revenu Québec within its own time limits (generally 90 days as well). Appeals of Quebec assessments go to the Court of Québec, not the Tax Court of Canada. A federal correction does not automatically change the Quebec return; you must make both.

Frequently asked questions

How long does a change take?

It depends on the method and the CRA's workload; online changes are generally processed faster than paper T1-ADJ forms. The CRA publishes service standards on canada.ca.

Will asking for a change trigger an audit?

A change request is processed like any return; the CRA may ask for documents to support it. Keep your receipts.

Can I claim a credit I forgot from 12 years ago?

Generally no. Requests are usually limited to the previous 10 calendar years.

Can I get help with an objection for free?

Some legal clinics and community programs help with benefit disputes. For tax disputes with significant amounts, a tax lawyer or CPA is often worth the fee.

Official sources

Canada Revenue Agency — Change my return, objections (T400A) and taxpayer relief (RC4288)
Tax Court of Canada — appeals and the informal procedure
Office of the Taxpayers' Ombudsperson — service complaints
Justice Laws Website — sections 152, 165 and 169 of the Income Tax Act
Revenu Québec — Quebec adjustments and objections